Vaccine hesitancy is a delay in acceptance or refusal of vaccines despite availability and supporting evidence of effectivity. The term also includes accepting vaccines but remaining uncertain about their use or using certain vaccines but not others. Although adverse effects associated with vaccines are occasionally observed, the scientific consensus that vaccines are generally safe and effective is overwhelming. Vaccine hesitancy often results in disease outbreaks and deaths from vaccine-preventable diseases. Therefore, the World Health Organization characterizes vaccine hesitancy as one of the top ten global health threats. Vaccine hesitancy is complex and context-specific, varying across time, place, and specific vaccine. It can be influenced by factors such as lack of proper scientific-based knowledge and understanding about how vaccines are made or work. Other possible factors include a fear of needles, distrust of or lack of confidence in public authorities (including healthcare providers) and/or the vaccine, complacency (the person does not see a need for the vaccine or does not see the value in it), and convenience (access to vaccines). It has existed since the invention of vaccination and pre-dates the coining of the terms "vaccine" and "vaccination" by nearly eighty years. Although myths, conspiracy theories, misinformation, and disinformation spread by the anti-vaccination movement and fringe doctors lead to vaccine hesitancy and public debates around the medical, ethical, and legal issues related to vaccines, there is no serious hesitancy or debate within mainstream medical and scientific circles about the benefits of vaccination. Opposition to mandatory vaccination may be based on anti-vaccine sentiment, concern that it violates civil liberties, reduces public trust in vaccination, or suspicion of profiteering by the pharmaceutical industry.
Safety concerns As with any medical treatment, there is potential for vaccines to cause serious complications such as allergic reactions, but unlike other interventions, vaccines are given to healthy people and so require a higher safety standard. Serious complications are extremely rare and much less common than risks from diseases they prevent. As the success of immunization programs increases, public attention may shift away from the risks of disease to the risk of vaccination, undermining public support for vaccination programs. The success of vaccinations has made certain diseases rare, and consequently led to incorrect heuristic thinking in weighing risks and benefits among the vaccine-hesitant. Once such diseases (e.g., Haemophilus influenzae B) decrease in prevalence, people may no longer appreciate how serious the illness is due to a lack of familiarity with it, and become complacent. The lack of personal experience with these diseases reduces the perceived danger and thus reduces the perceived benefit of immunization. Conversely, certain illnesses (e.g., influenza) remain so common that vaccine-hesitant people mistakenly perceive the illness to be non-threatening despite clear evidence that the illness poses a significant threat to human health. Omission and disconfirmation biases also contribute to vaccine hesitancy. Concerns about immunization safety often follow a pattern. First, some investigators suggest that a medical condition of increasing prevalence or unknown cause is an adverse effect of vaccination. The initial study and subsequent studies by the same group have an inadequate methodology, typically a poorly controlled or uncontrolled case series. A premature announcement is made about the alleged adverse effect, resonating with individuals who have the condition, and underestimating the potential harm of forgoing vaccination to those whom the vaccine could protect. Other groups attempt to replicate the initial study but fail to get the same results. Finally, it takes several years to regain public confidence in the vaccine. Adverse effects ascribed to vaccines typically have an unknown origin, an increasing incidence, some biological plausibility, occurrences close to the time of vaccination, and dreaded outcomes. In almost all cases, the public health effect is limited by cultural boundaries: English speakers worry about one vaccine causing autism, while French speakers worry about another vaccine causing multiple sclerosis, and Nigerians worry that a third vaccine causes infertility.
Ingredients concerns
Thiomersal
Thiomersal (called "thimerosal" in the US) is an antifungal preservative used in small amounts in some multi-dose vaccines (where the same vial is used for multiple patients) to prevent contamination. Thiomersal is metabolized or degraded by the body into ethylmercury (C2H5Hg+) and thiosalicylate. In 1999, the Centers for Disease Control (CDC) and the American Academy of Pediatrics (AAP) asked vaccine makers to remove thiomersal from vaccines on the precautionary principle. Thiomersal has been cleared from all common U.S. and European vaccines, except for some preparations of influenza vaccine. Trace amounts remain in some vaccines due to production processes, at an approximate maximum of one microgramme, around 15% of the average daily mercury intake in the U.S. for adults and 2.5% of the daily amount considered tolerable by the WHO. The action sparked concern that thiomersal could have been responsible for autism. This is considered disproven, as incidence rates for autism increased steadily even after thiomersal was removed. There is no accepted scientific evidence that exposure to thiomersal is a factor in causing autism. Since 2000, parents in the United States have pursued legal compensation from a federal fund arguing that thiomersal caused autism in their children. A 2004 Institute of Medicine (IOM) committee favored rejecting any causal relationship between thiomersal-containing vaccines and autism. The concentration of thiomersal used in vaccines as an antimicrobial agent ranges from 0.001% (1 part in 100,000) to 0.01% (1 part in 10,000). A vaccine containing 0.01% thiomersal has 25 micrograms of mercury per 0.5 mL dose, roughly the same amount of elemental mercury found in a three-ounce (85 g) can of tuna. There is robust peer-reviewed scientific evidence supporting the safety of thiomersal-containing vaccines.
Formaldehyde Vaccine-hesitant people have also voiced concerns about the presence of formaldehyde in vaccines. Formaldehyde is used in small concentrations to inactivate viruses and bacterial toxins used in vaccines. Small amounts of residual formaldehyde can be present in vaccines but are far below values harmful to human health. The levels present in vaccines are minuscule when compared to naturally occurring levels of formaldehyde in the human body and pose no significant risk of toxicity. The human body continuously produces formaldehyde naturally and contains 50–70 times the greatest amount of formaldehyde present in any vaccine. Furthermore, the human body is capable of breaking down naturally occurring formaldehyde as well as the small amount of formaldehyde present in vaccines. There is no evidence linking the infrequent exposures to small quantities of formaldehyde present in vaccines with cancer.
MMR vaccine
In the UK, the MMR vaccine was the subject of controversy after the publication in The Lancet of a 1998 paper by Andrew Wakefield and others reporting case histories of twelve children mostly with autism spectrum disorders with onset soon after administration of the vaccine. At a 1998 press conference, Wakefield suggested that giving children the vaccines in three separate doses would be safer than a single vaccination. This was not supported by the paper, and several subsequent peer-reviewed studies failed to show any association between the vaccine and autism. It later emerged that Wakefield had received funding from litigants against vaccine manufacturers and that he had not informed colleagues or medical authorities of his conflict of interest: Wakefield reportedly stood to earn up to $43 million per year selling diagnostic kits. Had this been known, publication in The Lancet would not have taken place in the way that it did. Wakefield has been heavily criticized on scientific and ethical grounds for the way the research was conducted and for triggering a decline in vaccination rates, which fell in the UK to 80% in the years following the study. In 2004, the MMR-and-autism interpretation of the paper was formally retracted by ten of its thirteen coauthors, and in 2010 The Lancet's editors fully retracted the paper. Wakefield was struck off the UK medical register, with a statement identifying deliberate falsification in the research published in The Lancet, and is barred from practicing medicine in the UK. The CDC, the IOM of the National Academy of Sciences, Australia's Department of Health, and the UK National Health Service have all concluded that there is no evidence of a link between the MMR vaccine and autism. A Cochrane review (2012, updated in 2020) concluded that there is no credible link between the MMR vaccine and autism, that MMR has prevented diseases that still carry a heavy burden of death and complications, that supports their use for mass immunization, that the lack of confidence in MMR has damaged public health, and that the design and reporting of safety outcomes in MMR vaccine studies are largely inadequate. Additional reviews agree, with studies finding that vaccines are not linked to autism even in high risk populations with autistic siblings. In 2009, The Sunday Times reported that Wakefield had manipulated patient data and misreported results in his 1998 paper, creating the appearance of a link with autism. A 2011 article in the British Medical Journal described how the data in the study had been falsified by Wakefield so that it would arrive at a predetermined conclusion. An accompanying editorial in the same journal described Wakefield's work as an "elaborate fraud" that led to lower vaccination rates, putting hundreds of thousands of children at risk and diverting energy and money away from research into the true cause of autism. A special court convened in the United States to review claims under the National Vaccine Injury Compensation Program ruled on February 12, 2009, that the evidence "failed to demonstrate that thimerosal-containing vaccines can contribute to causing immune dysfunction, or that the MMR vaccine can contribute to causing either autism or gastrointestinal dysfunction", and that parents of autistic children were therefore not entitled to compensation in their contention that certain vaccines caused autism in their children.
Vaccine overload Vaccine overload, a non-medical term, is the notion that administering many vaccines at once may overwhelm a child's immune system. The concept of vaccine overload is biologically implausible, as vaccinated and unvaccinated children have the same immune response to non-vaccine-related infections, and autism is not an immune-mediated disease. Claims that vaccines could overload the immune system go against current knowledge of the pathogenesis of autism. Despite the increase in the number of vaccines over recent decades, improvements in vaccine design have reduced the immunologic load from vaccines; the total number of immunological components in the 14 vaccines administered to US children in 2009 is less than 10 percent of vaccines given in 1980. A study published in 2013 found no correlation between autism and the antigen number in the vaccines administered up to the age of two. There were 1,008 children in the study, one quarter of whom were diagnosed with autism, and the cohort was born between 1994 and 1999, when the routine vaccine schedule could contain more than 3,000 antigens (in a single shot of DTP vaccine). The vaccine schedule in 2012 contained several more vaccines, but the number of antigens was 315. Vaccines pose small immunologic load compared to the pathogens naturally encountered by children. Common childhood conditions such as fevers and middle-ear infections pose a much greater challenge to the immune system than vaccines, and studies have shown that vaccinations, even multiple concurrent vaccinations, do not weaken the immune system or compromise overall immunity. The lack of evidence supporting the vaccine overload hypothesis, combined with these findings directly contradicting it, has led to the conclusion that currently recommended vaccine programs do not "overload" or weaken the immune system.
Prenatal infection Based on studies in animal models, theoretical concerns have been raised about a possible link between schizophrenia and maternal immune response activated by virus antigens. A 2009 review concluded that there was insufficient evidence to recommend routine use of trivalent influenza vaccine during the first trimester of pregnancy, but that the vaccine was still recommended outside the first trimester and in special circumstances such as pandemics or in women with certain other conditions. The CDC's Advisory Committee on Immunization Practices, the American College of Obstetricians and Gynecologists, and the American Academy of Family Physicians all recommend routine flu shots for pregnant women based on the risk for serious influenza-related complications, greater rates for flu-related hospitalizations compared to non-pregnant women, the possible transfer of maternal anti-influenza antibodies, and several studies failing to find harm to pregnant women or their children from the vaccinations. Despite this recommendation, only 16% of healthy pregnant US women surveyed in 2005 had been vaccinated against the flu.
Sudden infant death syndrome Sudden infant death syndrome (SIDS) is most common in infants around the time in life when they receive many vaccinations. Since the cause of SIDS has not been fully determined, this led to concerns about whether vaccines, in particular diphtheria-tetanus toxoid vaccines, were a possible causal factor. Several studies investigated this and found no evidence supporting a causal link between vaccination and SIDS. In 2003, the Institute of Medicine favored rejection of a causal link to DTwP vaccination and SIDS after reviewing the available evidence. Additional analyses of VAERS data also showed no relationship between vaccination and SIDS. Studies have shown a negative correlation between SIDs and vaccination. That is vaccinated children are less likely to die but no causal link has been found. One suggestion is that infants who are less likely to develop SIDS are more likely to be presented for vaccination.
Anthrax vaccines In the mid-1990s media reports on vaccines discussed the Gulf War Syndrome, a multi-symptomatic disorder affecting returning US military veterans of the 1990–1991 Persian Gulf War. Among the first articles of the online magazine Slate was one by Atul Gawande in which the required immunizations received by soldiers, including an anthrax vaccination, were named as one of the likely culprits for the symptoms associated with the Gulf War Syndrome. In the late 1990s Slate published an article on the "brewing rebellion" in the military against anthrax immunization because of "the availability to soldiers of vaccine misinformation on the Internet". Slate continued to report on concerns about the required anthrax and smallpox immunization for US troops after the September 11 attacks and articles on the subject also appeared on the Salon website. The 2001 anthrax attacks heightened concerns about bioterrorism and the Federal government of the United States stepped up its efforts to store and create more vaccines for American citizens. In 2002, Mother Jones published an article that was highly skeptical of the anthrax and smallpox immunization required by the United States Armed Forces. With the 2003 invasion of Iraq a wider controversy ensued in the media about requiring US troops to be vaccinated against anthrax. From 2003 to 2008 a series of court cases were brought to oppose the compulsory anthrax vaccination of US troops.
Swine flu vaccine
The U.S. swine flu immunization campaign in response to the 1976 swine flu outbreak has become known as "the swine flu fiasco" because the outbreak did not lead to a pandemic as U.S. President Gerald Ford had feared, and the hastily rolled out vaccine was found to increase the number of Guillain–Barré Syndrome cases two weeks after immunization. Government officials stopped the mass immunization campaign due to great anxiety about the safety of the swine flu vaccine. The general public was left with greater fear of the vaccination campaign than the virus itself, and vaccination policies, in general, were challenged. During the 2009 flu pandemic, significant controversy broke out regarding whether the 2009 H1N1 flu vaccine was safe in, among other countries, France. Numerous different French groups publicly criticized the vaccine as potentially dangerous. Because of similarities between the 2009 influenza A subtype H1N1 virus and the 1976 influenza A/NJ virus many countries established surveillance systems for vaccine-related adverse effects on human health. A possible link between the 2009 H1N1 flu vaccine and Guillain–Barré Syndrome cases was studied in Europe and the United States.
Blood transfusion After the introduction of COVID-19 vaccines, vaccine hesitant people have at times demanded that they get donor blood from donors that have not received the vaccine. In the US and Canada, blood centers do not keep data on whether a donor has been COVID-19 infected or vaccinated, and in August 2021 it was estimated that 60-70% of US blood donors had COVID-19 antibodies. Research director Timothy Caulfield said that "This really highlights, I think, how powerful misinformation can be. It can really have an impact in a way that can be dangerous ... There is no evidence to support these concerns." The British Journal of Haematology called the trend "alarming" in 2021. The chief medical officer of ImpactLife said the same year that accepting such a demand "would be an operational can of worms for a medically unjustifiable request". As of August 2021, such demands were rare in the US. As of 2024, the numbers are increasing. Doctors in Alberta, Canada, warned in November 2022 that the demands were becoming more common. The Association for the Advancement of Blood & Biotherapies (AABB) and the Canadian Blood Services have both issued guidance on how to respond to such demands. In Italy and New Zealand, parents have gone to court to stop their children's urgent heart surgery, unless COVID-19 vaccine free blood was provided. In both cases the parents were ruled against, though they stated that they could provide willing donors they found acceptable. The New Zealand Blood Service does not label blood according to the donor's COVID-19 vaccine history, and as of 2022, about 90% of New Zealand's population over twelve years of age has had two COVID-19 vaccinations. In another Italian case, a blood transfusion for a sick 90-year-old man was refused by his two daughters, due to vaccine hesitancy concerns. Another New Zealand couple stated that they were trying to arrange their child to have her next heart surgery in India, to avoid her being given blood from COVID-19 vaccinated donors.
Other safety concerns Other safety concerns about vaccines have been promoted on the Internet, in informal meetings, in books, and at symposia. These include hypotheses that vaccination can cause epileptic seizures, allergies, multiple sclerosis, and autoimmune diseases such as type 1 diabetes, as well as hypotheses that vaccinations can transmit bovine spongiform encephalopathy, hepatitis C virus, and HIV. These hypotheses have been investigated, with the conclusion that currently used vaccines meet high safety standards and that criticism of vaccine safety in the popular press is not justified. Large well-controlled epidemiologic studies have been conducted and the results do not support the hypothesis that vaccines cause chronic diseases. Furthermore, some vaccines are probably more likely to prevent or modify than cause or exacerbate autoimmune diseases. Another common concern parents often have is about the pain associated with administering vaccines during a doctor's office visit. This may lead to parental requests to space out vaccinations; however, studies have shown a child's stress response is not different when receiving one vaccination or two. The act of spacing out vaccinations may actually lead to more stressful stimuli for the child.
Vaccine myths and misinformation Several vaccination myths contribute to parental concerns and vaccine hesitancy. These include the alleged superiority of natural infection when compared to vaccination, questioning whether the diseases vaccines prevent are dangerous, whether vaccines pose moral or religious dilemmas, suggesting that vaccines are not effective, proposing unproven or ineffective approaches as alternatives to vaccines, and conspiracy theories that center on mistrust of the government and medical institutions. Nevertheless, despite a major measles outbreak in the United States Southwest which began February 2025 in an area of Texas with low measles immunization rates—perhaps due in part to vaccine misinformation—in March 2025, the U.S. National Institutes of Health and the Centers for Disease Control and Prevention, under the direction of Secretary of Health and Human Services Robert F. Kennedy Jr., abruptly cancelled funding for over 40 research grants studying vaccine hesitancy.
Autism
The idea of a link between vaccines and autism has been extensively investigated and conclusively shown to be false. The scientific consensus is that there is no relationship, causal or otherwise, between vaccines and incidence of autism, and vaccine ingredients do not cause autism. Nevertheless, the anti-vaccination movement continues to promote myths, conspiracy theories, and misinformation linking the two. A developing tactic described by Skeptical Inquirer appears to be the "promotion of irrelevant research [as] an active aggregation of several questionable or peripherally related research studies in an attempt to justify the science underlying a questionable claim".
Vaccination during illness Many parents are concerned about the safety of vaccination when their child is sick. Moderate to severe acute illness with or without a fever is indeed a precaution when considering vaccination. Vaccines remain effective during childhood illness. The reason vaccines may be withheld if a child is moderately to severely ill is because certain expected side effects of vaccination (e.g. fever or rash) may be confused with the progression of the illness. It is safe to administer vaccines to well-appearing children who are mildly ill with the common cold.
Natural infection Another common anti-vaccine myth is that the immune system produces a better immune protection in response to natural infection when compared to vaccination. However, strength and duration of immune protection gained varies by both disease and vaccine, with some vaccines giving better protection than natural infection. For example, the HPV vaccine generates better immune protection than natural infection due to the vaccine containing higher concentrations of a viral coat protein, while also not containing proteins the HPV viruses use to inhibit immune response. While it is true that infection with certain illnesses may produce lifelong immunity, many natural infections do not produce lifelong immunity, while carrying a higher risk of harming a person's health than vaccines. For example, natural varicella infection carries a higher risk of bacterial superinfection with Group A streptococci. Natural measles infection carries a high risk of many serious, and sometimes life-long, complications, all of which can be avoided by vaccination. Those infected with measles rarely have a symptomatic reinfection. Most people survive measles, though in some cases, complications may occur. Among those that experience complications, about 1 in 4 individuals will be hospitalized and 1–2 in 1000 will die. Complications are more likely in children under age 5 and adults over age 20. Pneumonia is the most common fatal complication of measles infection and accounts for 56–86% of measles-related deaths. Possible consequences of measles virus infection include laryngotracheobronchitis, sensorineural hearing loss, and—in about 1 in 10,000 to 1 in 300,000 cases—panencephalitis, which is usually fatal. Acute measles encephalitis is another serious risk of measles virus infection. It typically occurs two days to one week after the measles rash breaks out and begins with very high fever, severe headache, convulsions and altered mentation. A person with measles encephalitis may become comatose, and death or brain injury may occur. The measles virus can deplete previously acquired immune memory by killing cells that make antibodies, and thus weakens the immune system which can cause deaths from other diseases. Suppression of the immune system by measles lasts about two years and has been epidemiologically implicated in up to 90% of childhood deaths in third world countries, and historically may have caused rather more deaths in the United States, the UK and Denmark than were directly caused by measles. Although the measles vaccine contains an attenuated strain, it does not deplete immune memory.
HPV vaccine The idea that the HPV vaccine is linked to increased sexual behavior is not supported by scientific evidence. A review of nearly 1,400 adolescent girls found no difference in teen pregnancy, the incidence of sexually transmitted infection, or contraceptive counseling regardless of whether they received the HPV vaccine. Thousands of Americans die each year from cancers preventable by the vaccine. There remains a disproportionate rate of HPV-related cancers amongst LatinX populations, leading researchers to explore how messaging may be made more effective to address vaccine hesitancy.
Vaccine schedule Other concerns have been raised about the vaccine schedule recommended by the Advisory Committee on Immunization Practices (ACIP). The immunization schedule is designed to protect children against preventable diseases when they are most vulnerable. The practice of delaying or spacing out these vaccinations increases the amount of time the child is susceptible to these illnesses. Receiving vaccines on the schedule recommended by the ACIP is not linked to autism or developmental delay.
Information warfare An analysis of tweets from July 2014 through September 2017 revealed an active campaign on Twitter by the Internet Research Agency (IRA), a Russian troll farm accused of interference in the 2016 U.S. elections, to sow discord about the safety of vaccines. The campaign used sophisticated Twitter bots to amplify polarizing pro-vaccine and anti-vaccine messages, containing the hashtag #VaccinateUS, posted by IRA trolls. Throughout 2020 and 2021, the United States ran a propaganda campaign to spread disinformation about the Sinovac Chinese COVID-19 vaccine, including using fake social media accounts to spread the disinformation that the Sinovac vaccine contained pork-derived ingredients and was therefore haram under Islamic law. The campaign primarily targeted people in the Philippines and used a social media hashtag for "China is the virus" in Tagalog.
Sanitation There is anti-vaccine literature that argues that reductions in infectious disease result from improved sanitation and hygiene (rather than vaccination) or that these diseases were already in decline before the introduction of specific vaccines. These claims are not supported by scientific data; the incidence of vaccine-preventable diseases tended to fluctuate over time until the introduction of specific vaccines, at which point the incidence dropped to near zero. A Centers for Disease Control and Prevention website aimed at countering common misconceptions about vaccines argued, "Are we expected to believe that better sanitation caused the incidence of each disease to drop, just at the time a vaccine for that disease was introduced?"
Alternative medicine
Many forms of alternative medicine are based on philosophies that oppose vaccination (including germ theory denialism) and have practitioners who voice their opposition. As a consequence, the increase in popularity of alternative medicine in the 1970s planted the seeds of the modern anti-vaccination movement. More specifically, some elements of the chiropractic community, some homeopaths, and naturopaths developed anti-vaccine rhetoric. The reasons for this negative vaccination view are complicated and rest at least in part on the early philosophies that shaped the foundation of these groups.
Chiropractic
Historically, chiropractic strongly opposed vaccination based on its belief that all diseases were traceable to so-called "vertebral subluxations" in the spine and therefore could not be affected by vaccines. Daniel D. Palmer (1845–1913), the founder of chiropractic, wrote: "It is the very height of absurdity to strive to 'protect' any person from smallpox or any other malady by inoculating them with a filthy animal poison." Vaccination remains controversial within the profession. Most chiropractic writings on vaccination focus on its negative aspects. A 1995 survey of US chiropractors found that about one third believed there was no scientific proof that immunization prevents disease. While the Canadian Chiropractic Association supports vaccination, a survey in Alberta in 2002 found that 25% of chiropractors advised patients for, and 27% advised against, vaccinations for patients or for their children. Although most chiropractic colleges try to teach about vaccination in a manner consistent with scientific evidence, several have faculty who seem to stress negative views. A survey of a 1999–2000 cross-section of students of Canadian Memorial Chiropractic College (CMCC), which does not formally teach anti-vaccination views, reported that fourth-year students opposed vaccination more strongly than did first-year students, with 29.4% of fourth-year students opposing vaccination. A follow-up study on 2011–12 CMCC students found that pro-vaccination attitudes heavily predominated. Students reported support rates ranging from 84% to 90%. One of the study's authors proposed the change in attitude to be due to the lack of the previous influence of a "subgroup of some charismatic students who were enrolled at CMCC at the time, students who championed the Palmer postulates that advocated against the use of vaccination".
Policy positions The American Chiropractic Association and the International Chiropractic Association support individual exemptions to compulsory vaccination laws. In March 2015, the Oregon Chiropractic Association invited Andrew Wakefield, chief author of a fraudulent research paper, to testify against Senate Bill 442, "a bill that would eliminate nonmedical exemptions from Oregon's school immunization law". The California Chiropractic Association lobbied against a 2015 bill ending belief exemptions for vaccines. They had also opposed a 2012 bill related to vaccination exemptions.
Homeopathy
Several surveys have shown that some practitioners of homeopathy, particularly homeopaths without any medical training, advise patients against vaccination. For example, a survey of registered homeopaths in Austria found that only 28% considered immunization an important preventive measure, and 83% of homeopaths surveyed in Sydney, Australia, did not recommend vaccination. Many practitioners of naturopathy also oppose vaccination. Homeopathic "vaccines" (nosodes) are ineffective because they do not contain any active ingredients and thus do not stimulate the immune system. They can be dangerous if they take the place of effective treatments. Some medical organizations have taken action against nosodes. In Canada, the labeling of homeopathic nosodes require the statement: "This product is neither a vaccine nor an alternative to vaccination."
Financial motives Alternative medicine proponents gain from promoting vaccine conspiracy theories through the sale of ineffective and expensive medications, supplements, and procedures such as chelation therapy and hyperbaric oxygen therapy, sold as able to cure the 'damage' caused by vaccines. Homeopaths in particular gain through the promotion of water injections or 'nosodes' that they allege have a 'natural' vaccine-like effect. Additional bodies with a vested interest in promoting the "unsafeness" of vaccines may include lawyers and legal groups organizing court cases and class action lawsuits against vaccine providers. Conversely, alternative medicine providers have accused the vaccine industry of misrepresenting the safety and effectiveness of vaccines, covering up and suppressing information, and influencing health policy decisions for financial gain. In the late 20th century, vaccines were a product with low profit margins, and the number of companies involved in vaccine manufacture declined. In addition to low profits and liability risks, manufacturers complained about low prices paid for vaccines by the CDC and other US government agencies. In the early 21st century, the vaccine market greatly improved with the approval of the vaccine Prevnar, along with a small number of other high-priced blockbuster vaccines, such as Gardasil and Pediarix, which each had sales revenues of over $1 billion in 2008. Despite high growth rates, vaccines represent a relatively small portion of overall pharmaceutical profits. As recently as 2010, the World Health Organization estimated vaccines to represent 2–3% of total sales for the pharmaceutical industry.
Psychological factors The rise in vaccine hesitancy has led to research on the psychology of those who actively oppose vaccines. The largest psychological factors leading to anti-vaccination attitudes are conspiratorial thinking, reactance, disgust regarding blood or needles, and individualistic or hierarchical worldviews. In contrast, demographic variables are not significant. Researchers have also investigated the psychological roots of vaccine hesitancy with regard to specific vaccines. For instance, a 2021 study published in Nature Communications investigated psychological characteristics associated with COVID-19 vaccine hesitancy and resistance in Ireland and the UK. The study found that vaccine hesitant or resistant respondents in the two countries varied across socio-demographic and health-related variables, however, they were similar in range of psychological factors. Such respondents were less likely to obtain information about the pandemic from authoritative and traditional media sources and demonstrated similar skepticism towards these sources compared to respondents who accepted the vaccine.
Fear of needles Blood-injection-injury phobia and general fear of needles and injections can lead people to avoid vaccinations. One survey conducted in January and February 2021 estimated this was responsible for 10% of the COVID-19 vaccine hesitancy in the UK at the time. A 2012 survey of American parents found that a fear of needles was the most common reason for adolescents to forgo their second dose of a HPV vaccine. Various treatments for fear of needles can help overcome this problem, from offering pain reduction at the time of injection to long-term behavioral therapy. Tensing the stomach muscles can help avoid fainting, swearing can reduce perceived pain, and distraction can also improve the perceived experience, such as by pretending to cough, performing a visual task, watching a video, or playing a video game. To avoid dissuading people who have a needle phobia, vaccine update researchers recommend against using pictures of needles, people getting an injection, or faces displaying negative emotions (like a crying baby) in promotional materials. Instead, they recommend medically accurate photos depicting smiling, diverse people with bandages, vaccination cards, or a rolled-up sleeve; depicting vials instead of needles; and depicting the people who develop and test vaccines. Development of vaccines that can be administered orally or with a jet injector can also avoid triggering the fear of needles.
Social and political Beyond misinformation, social and economic conditions also influence how many people take vaccines. Factors such as income, socioeconomic status, ethnicity, age, and education can determine the uptake of vaccines and their impact, especially among vulnerable communities. Social factors like whether one lives with others may affect vaccine uptake. For example, older individuals who live alone are much more likely not to take up vaccines compared to those living with other people. Other factors may be racial, with minority groups being affected by low vaccine uptake. People with weaker immune systems or chronic illness are more likely to take up a vaccine if recommended by their physicians. Politicization of medicine was found associated with vaccine hesitancy.
Malpractice and fraud
Unethical human experimentation and medical racism Some people in groups experiencing medical racism are less willing to trust doctors and modern medicine due to real historical incidents of unethical human experimentation and involuntary sterilization. Famous examples include drug trials in Africa without informed consent, the Guatemala syphilis experiments, the Tuskegee Syphilis Study, the culturing of cells from Henrietta Lacks without consent, and Nazi human experimentation. To overcome this type of distrust, experts recommend including representative samples of majority and minority populations in drug trials, including minority groups in study design, being diligent about informed consent, and being transparent about the process of drug design and testing.
CIA fake vaccination clinic
In Pakistan, the CIA ran a fake vaccination clinic in an attempt to locate Osama bin Laden. As a direct consequence, there have been several attacks and deaths among vaccination workers. Several Islamist preachers and militant groups, including some factions of the Taliban, view vaccination as a plot to kill or sterilize Muslims. Efforts to eradicate polio have furthermore been disrupted by American drone strikes. Pakistan is among the only countries where polio remained endemic as of 2015.
Fake COVID-19 vaccines In July 2021, Indian police arrested 14 people for administering doses of saline solution instead of the AstraZeneca vaccine at nearly a dozen private vaccination sites in Mumbai. The organizers, including medical professionals, charged between $10 and $17 for each dose, and more than 2,600 people paid to receive what they thought was the vaccine. The federal government downplayed the scandal, claiming these cases were isolated. McAfee stated India was among the top countries to have been targeted by fake apps to lure people with a promise of vaccines. In Bhopal, slum residents were misled into thinking they would get an approved COVID-19 vaccine, but instead were actually part of an experimental clinical trial for the domestic vaccine Covaxin. Only 50% of participants in the trials received a vaccine with the rest receiving a placebo. One participant stated, "...I didn't know that there was a possibility you could get a water shot."
Religion
Since most religions predate the invention of vaccines, scriptures do not specifically address the topic of vaccination. However, vaccination has been opposed by some on religious grounds ever since it was first introduced. When vaccination was first becoming widespread, some Christian opponents argued that preventing smallpox deaths would be thwarting God's will and that such prevention is