science

Influenza B virus

Influenza B virus is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Influenza B virus rather than just read about it. In short: Influenza B virus is the only species in the genus Betainfluenzavirus in the virus family Orthomyxoviridae. Influenza B virus is a negative-sense single-strand RNA virus known only to infect certain mammal species, including humans, ferrets, pigs, and seals.

Key takeaways

Influenza B virus belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Influenza B virus to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Influenza B virus from memory before moving on to harder problems.

Reference excerpt

Influenza B virus is the only species in the genus Betainfluenzavirus in the virus family Orthomyxoviridae. Influenza B virus is a negative-sense single-strand RNA virus known only to infect certain mammal species, including humans, ferrets, pigs, and seals. This limited host range is apparently responsible for the lack of influenza pandemics associated with influenza B virus, in contrast with those caused by the morphologically similar influenza A virus, as both mutate by both antigenic drift and reassortment. Nevertheless, it is accepted that influenza B virus could cause significant morbidity and mortality worldwide, and significantly impacts adolescents and schoolchildren. Until 2020, two distinct lineages of influenza B virus co-circulated in humans. Known as B/Yamagata and B/Victoria, these lineages are distinguished by differences in the antigenic structure of the surface glycoprotein hemagglutinin (HA) and their varying abilities to elicit innate immune responses in the host. However, the B/Yamagata lineage may have become extinct in 2020/2021 due to COVID-19 pandemic measures. In October 2023, the World Health Organization concluded that protection against the Yamagata lineage was no longer necessary in the seasonal flu vaccine, reducing the number of lineages targeted by the vaccine from four to three. For the 2024–2025 Northern Hemisphere influenza season, the US Food and Drug Administration (FDA) recommends removing B/Yamagata from all influenza vaccines. The European Medicines Agency (EMA) recommends removing B/Yamagata from influenza vaccines for the 2024–2025 seasonal flu vaccine composition.

Morphology The influenza B virus capsid is enveloped while its virion consists of an envelope, a matrix protein, a nucleoprotein complex, a nucleocapsid, and a polymerase complex. It is sometimes spherical and sometimes filamentous. Its 500 or so surface projections are made of hemagglutinin and neuraminidase.

Genome structure and genetics The influenza B virus genome is 14,548 nucleotides long and consists of eight segments of linear negative-sense, single-stranded RNA. The multipartite genome is encapsidated, each segment in a separate nucleocapsid, and the nucleocapsids are surrounded by one envelope. The ancestor of influenza viruses A and B and the ancestor of influenza virus C are estimated to have diverged from a common ancestor around 8,000 years ago. Influenza viruses A and B are estimated to have diverged from a single ancestor around 4,000 years ago, while the subtypes of influenza A virus are estimated to have diverged 2,000 years ago. Metatranscriptomics studies have also identified closely related "influenza B-like" viruses such as the Wuhan spiny eel influenza virus and also "influenza B-like" viruses in a number of vertebrate species such as salamanders and fish. Diminishing the impact of this virus is the fact that, "in humans, influenza B viruses evolve slower than A viruses and faster than C viruses". Influenza B virus mutates at a rate 2 to 3 times slower than type A.

Vaccine In 1936, Thomas Francis Jr. discovered the ferret influenza B virus. Also in 1936, Macfarlane Burnet made the discovery that influenza virus may be cultured in hen embryonated eggs. This prompted research into the properties of the virus and the creation and application of inactivated vaccines in the late 1930s and early 1940s. Inactivated vaccines' usefulness as a preventative measure was proven in the 1950s. Later, 2003 saw the approval of the first live, attenuated influenza vaccine. Looking into influenza B specifically, Thomas Francis Jr. isolated influenza B virus in 1936. However, it was not until 1940 that influenza B viruses were discovered. In 1942, a new bivalent vaccine was developed that protected against both the H1N1 strain of influenza A and the newly discovered influenza B virus. The viruses included in flu vaccines are changed each year. Even though there have been two different lineages of influenza B viruses that were circulating during most seasons, flu vaccinations were long meant to protect against three different flu viruses: the influenza A(H1N1), influenza A(H3N2), and one type of influenza B virus. The second lineage of the B virus was since added to provide greater defense against circulating flu viruses. Two influenza A viruses and two influenza B viruses have up until 2023 been among the four flu viruses that a quadrivalent vaccine was intended to protect against. As of 2022 all flu vaccines in the United States were quadrivalent. The four main types of type A and B influenza viruses that are most likely to spread and make people sick during the upcoming flu season have been the targets of seasonal influenza (flu) vaccines. All of the available flu vaccinations in the United States have offered protection against the influenza A(H1), A(H3), B/Yamagata, and B/Victoria lineage viruses. Each of these four vaccine virus components has been chosen based on which flu viruses are infecting people ahead of the upcoming flu season, how widely they are spreading, how well the vaccines from the previous flu season may protect against those flu viruses, and the vaccine viruses' capacity to offer cross-protection. For the 2022–2023 flu season, there were three flu vaccines that were preferentially recommended for people 65 years and older; various influenza (flu) vaccinations are authorized for use in people of various age groups. However, the B/Yamagata lineage might have become extinct in 2020 due to COVID-19 pandemic measures, and there have been no naturally occurring cases confirmed since March 2020. In October 2023, the World Health Organization concluded that protection against the Yamagata lineage was no longer necessary in the seasonal flu vaccine, reducing the number of lineages targeted by the vaccine from four to three. If the virus has indeed gone extinct, it would be the first documented case of a virus going extinct due to changes in human behavior. However, the overall burden of the influenza virus would be similar to past seasons because there are still three remaining strains widely circulating.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Influenza B virus

Start with the simplest possible case. Write down what Influenza B virus claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Influenza B virus before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Influenza B virus ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Influenza B virus

In research: Influenza B virus appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Influenza B virus in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Influenza B virus is common in secondary-school and first-year university syllabi. It links to neighbouring topics Influenza, Orthomyxoviridae, so understanding it makes those chapters shorter.
In everyday life: Look for Influenza B virus outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Influenza B virus in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Influenza B virus means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Influenza B virus out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Influenza B virus in simple terms?

Why does Influenza B virus matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Influenza B virus?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Influenza B virus.