Moderna COVID-19 vaccine

The Moderna COVID‑19 vaccine, sold under the brand name Spikevax among others, is a COVID-19 vaccine developed by the American company Moderna, the United States National Institute of Allergy and Infectious Diseases (NIAID), and the Biomedical Advanced Research and Development Authority (BARDA). Depending on the jurisdiction, it is authorized for use in humans aged six months, twelve years, or eighteen years and older. The Moderna COVID‑19 vaccine provides protection against COVID-19, which is caused by infection by the SARS-CoV-2 virus. A different version of the Moderna COVID-19 vaccine, sold under the brand name Mnexspike (mRNA-1283), was approved for medical use in the United States in May 2025, and in the European Union in February 2026. Spikevax is designed to be administered in two or three 0.5-mL doses given by intramuscular injection, primarily into the deltoid muscle, at an interval of at least 28 days apart. The World Health Organization advises an eight-week interval between doses to optimize efficacy. Additional booster doses are approved in some regions to maintain immunity. Clinical trials and real-world data have demonstrated the vaccine's high efficacy, with significant effectiveness observed two weeks post-administration of the second dose, offering 94% protection against Covid and robust defense against severe cases. The vaccine's efficacy spans various demographics, including age, sex, and those with high-risk medical conditions. Spikevax is an mRNA vaccine composed of nucleoside-modified mRNA (modRNA) encoding a spike protein of SARS-CoV-2, which is encapsulated in lipid nanoparticles. In August and September 2022, bivalent versions of the vaccine (Moderna COVID-19 Vaccine, Bivalent) containing elasomeran/elasomeran 0-omicron (Spikevax Bivalent Zero/Omicron) were authorized for use as booster doses in individuals aged 18 or older in the United Kingdom, Switzerland, Australia, Canada, the European Union, and the United States. The second component of the version of the bivalent vaccine used in the United States is based on the Omicron BA.4/BA.5 variant, while the second component of the bivalent vaccine version used in other countries is based on the Omicron BA.1 variant. The vaccine's effectiveness against variants has been extensively studied, indicating varying degrees of protection. For instance, during the prevalence of the Delta variant, effectiveness against infection slightly decreased over time. The vaccine's longevity and continuous protection are under study, with ongoing research focusing on its duration of effectiveness, which remains partially undetermined as of the latest updates. The safety profile of the vaccine is favorable, with common side effects including injection site pain, fatigue, and headaches. Severe reactions like anaphylaxis are exceedingly rare. Concerns regarding myocarditis, have been identified but are typically mild and manageable. The vaccine's formulation utilizes mRNA technology, encapsulated within lipid nanoparticles to ensure cellular uptake and immune system response.

Medical uses The Moderna COVID‑19 vaccine is used to provide protection against infection by the SARS‑CoV‑2 virus in order to prevent COVID‑19. The vaccine is given by intramuscular injection into the deltoid muscle of the arm. The initial course consists of two doses. The World Health Organization (WHO) recommends an interval of eight weeks between doses. A third, fourth, or fifth dose can be added in some countries.

Efficacy

Evidence of vaccine efficacy starts about two weeks after the first dose. High efficacy is achieved with full immunization, two weeks after the second dose, and was evaluated at 94.1%: at the end of the vaccine study that led to emergency authorization in the US, there were eleven cases of COVID‑19 in the vaccine group (out of 15,181 people) versus 185 cases in the placebo group (15,170 people). Moreover, there were zero cases of severe COVID‑19 in the vaccine group, versus eleven in the placebo group. This efficacy has been described as "astonishing" and "borderline historic" for a respiratory virus vaccine, and it is similar to the efficacy of the Pfizer–BioNTech COVID-19 vaccine. Efficacy estimates were similar across age groups, sexes, racial and ethnic groups, and participants with medical comorbidities associated with high risk of severe COVID‑19. Only individuals aged 18 or older were studied. Studies are underway to gauge efficacy and safety in children aged 0–11 (KidCOVE) and 12–17 (TeenCOVE). A further study conducted by the US Centers for Disease Control and Prevention (CDC) between December 2020, and March 2021, on nearly 4 thousand health care personnel, first responders, and other essential and frontline workers concluded that under real-world conditions, mRNA vaccine effectiveness of full immunization (14 days or more after second dose) was 90% against SARS-CoV-2 infections, regardless of symptoms, and vaccine effectiveness of partial immunization (14 days or more after first dose but before second dose) was 80%. The duration of protection provided by the vaccine is unknown as of April 2021, and a two-year followup study is underway to determine the duration. Preliminary results from a phase III trial indicate that vaccine efficacy is durable, remaining at 93% six months after the second dose.

Effectiveness A vaccine is generally considered effective if the estimate is ≥50% with a >30% lower limit of the 95% confidence interval. Effectiveness is generally expected to slowly decrease over time. In August 2021, results from a study suggested that the effectiveness against infection decreased from 91% (81–96%) to 66% (26–84%) when the Delta variant became predominant in the US, which may be due to unmeasured and residual confounding related to a decline in vaccine effectiveness over time.

Specific populations Limited data are available on the safety of the Moderna COVID‑19 vaccine during pregnancy. The initial study excluded pregnant women or discontinued them from vaccination upon a positive pregnancy test. Studies in animals found no safety concerns and clinical trials are underway to evaluate the safety and efficacy of COVID‑19 vaccines in pregnant women. Real-world observations through the CDC v-safe tracking program have not uncovered unusual numbers of adverse events or outcomes of interest. Based on the results of a preliminary study, the US CDC recommends that pregnant women get vaccinated with the COVID‑19 vaccine.

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