Influenza B virus

Understanding Influenza B: A Closer Look at the Invisible Threat

Influenza B virus, often overshadowed by its more notorious cousin, influenza A, is a fascinating yet elusive entity. It’s like a stealthy intruder in the world of respiratory viruses, with a limited host range that primarily targets humans, ferrets, pigs, and seals. But why hasn’t it caused pandemics? Is it because of its limited antigenic drift and reassortment capabilities, or is there more to the story?

The Two Lineages: A Tale of B/Yamagata and B/Victoria

There are two known lineages, B/Yamagata/16/88-like and B/Victoria/2/87-like. These lineages have been the focus of much attention in recent years, especially with the development of a quadrivalent vaccine that has shown greater effectiveness since 2016. However, the World Health Organization recently concluded that protection against the Yamagata lineage is no longer necessary, reducing the number of lineages targeted by vaccines from four to three.

The Structure and Functionality of Influenza B

The influenza B virus genome consists of eight segments of linear negative-sense, single-stranded RNA. This unique structure includes an envelope, matrix protein, nucleoprotein complex, and polymerase complex. It’s like a well-organized team with each member playing a crucial role in the virus’s survival and spread.

A Century of Vaccination: From Bivalent to Quadrivalent

Since 1942, when a bivalent vaccine was developed protecting against H1N1 and influenza B virus, we’ve come a long way. Today’s flu vaccines still use science from nearly a century ago, but the viruses included in these vaccines change each year to match the most likely strains of flu that make people sick. Flu vaccinations have protected against three types of flu viruses: A(H1N1), A(H3N2), and one type of B virus.

The Shift to Quadrivalent Vaccines

Since 2022, all US flu vaccines were quadrivalent, targeting two influenza A viruses and two B viruses. The four main types of flu viruses targeted are A(H1), A(H3), B/Yamagata, and B/Victoria. In March 2022, the FDA proposed using three specific strains for trivalent vaccines. However, in October 2023, the World Health Organization concluded that protection against the Yamagata lineage was no longer necessary.

The Evolution of Influenza B: A Constant Struggle

Influenza B virus was discovered in 1940, with two lineages (Yamagata and Victoria) circulating during most seasons. The viruses’ HA and NA surface antigens change constantly, leading to antigenic drift or shift, making it essential to update the vaccine ingredient list annually. Hemagglutination inhibition experiments using ferret serum after infection allowed the identification of two different antigenic influenza type B variants in 1988-1989, sharing antigens with either B/Yamagata/16/88 or B/Victoria/2/87 viruses.

Reinfection and Genetic Changes

In Japan, influenza B virus reinfection was investigated virologically and epidemiologically from 1979 to 1991, resulting in four antigenic drift outbreaks. Between epidemics, there was significant genetic and antigenic change in the viruses, with a minimum rate of reinfection ranging from 2 to 25%. Reinfection occurred with viruses recovered during the 1984-1985 and 1987-1988 seasons, which belonged to the same lineage and were antigenically close. The B/Yamagata lineage might be extinct as a result of COVID-19 pandemic measures, but continued surveillance is required due to past pauses in IBV circulation.

Condensed Infos to Influenza B virus

As we continue to navigate the complex world of influenza, it’s clear that understanding and adapting to the ever-changing landscape of viruses like Influenza B is crucial. The journey from bivalent to quadrivalent vaccines reflects our ongoing efforts to protect public health. Whether the Yamagata lineage will truly disappear or if it will make a comeback remains to be seen, but one thing is certain: vigilance and adaptability are key in this ever-evolving battle against viruses.