How COVID-19 pandemic has wiped off a lineage of flu virus

It is hard to believe that a pandemic can have some positive impact, especially when horrors of a recent such event are fresh in memories of the people. Irony it is, but scientists have suggested that one particular lineage of the influenza virus, responsible for seasonal epidemics have been wiped off partly due to the health measures taken during the COVID-19 pandemic.

America has recently announced dropping of the vaccine against this lineage. The public health measures like mask wearing, physical distancing or maintaining better ventilation etc. seem to have eliminated the B/Yamagata lineage of the flu virus. There have been no confirmed cases since March 2020.

On September 23, 2023, the World Health Organisation (WHO) came out with the recommendation that it is no longer needed to include the components against B/Yamagata in the yearly vaccine routine. On March 5, one of the expert panel of the US FDA (Food and Drug Administration) voted unanimously that B/Yamagata be removed from the flu vaccine regime.

Yamagata lineage and other types of flu virus

What we generally call ‘flu’ manifesting seasonal outbreaks across the world is a viral disease attacking the respiratory system. This so-called ‘flu’ erupts due to infection caused by the influenza virus, which spreads easily among people through small droplets coming out from an infected person while sneezing or coughing.

Influenza virus is categorised into four types, namely A, B, C and D, each having their own characteristic behaviour of infection and disease severity. Influenza types A and B circulate and cause seasonal epidemics. Influenza A is the only type known to have caused pandemic — “The A(H1N1) is also written as A(H1N1)pdm09 as it caused the pandemic in 2009 and replaced the previous A(H1N1) virus which had circulated prior to 2009,” writes WHO. This type is also widespread in other mammals including pigs. The H1N1 virus of 2009 pandemic is popularly known as the ‘swine flu’, which is a sub-type of Influenza A virus that can infect humans, pigs and birds.

Influenza B and C primarily infect humans, while type D is primarily found in cattle without any known event of infecting or causing illness in people. Type C causes very mild symptoms and is detected very less frequently and that’s why it is not considered an important public health issue.

The Yamagata lineage belongs to type B influenza virus. In fact, the B type is divided into two lineages, namely the Yamagata and Victoria and are written as B/Yamagata and B/Victoria. Viral lineages depict a group of closely related viruses that diverged from a common ancestor at some point of evolution. This means B/Yamagata and B/Victoria shared a common ancestor and now share close relation in their genetic make-up.

The B/Yamagata showed substantial drop since the start of the COVID-19 pandemic and after March 2020 this virus has not been isolated or sequenced. As the Lancet editorial of December 2023 says, the dropping of infection by B/Yamagata lineage is likely due to vaccine composition previously. And afterwards, with the strict health measures during COVID-19 pandemic the lineage has dropped totally from circulation.

Flu vaccines and the new change

Vaccination has been an established strategy against influenza epidemics in many countries of the world including the United States. As per data of CDC (Centre for Disease Control and Prevention), USA, flu vaccines have been used in the country for the past 50 years.

Regarding the flu vaccines, valency plays an important role, which essentially is the vaccine composition. These vaccines have been either trivalent or quadrivalent. Trivalent flu vaccines have the ability of protecting against three different influenza viruses and accordingly the quadrivalent will protect against four types of the virus. The trivalent vaccines include antigens such as vaccine viruses or viral proteins from three different viruses and the quadrivalent will include four such antigens.

It is worth remembering quickly that in vaccine administration, a person is injected with the pathogen (any agent like virus, bacteria or fungi etc. that can cause a disease) or a part of it before getting infected. In this process, our immune system (the defense mechanism of the body) learns how to fight against the pathogen in future when infection really happens. The immune system creates memory as part of its (immune) response against the pathogen. In vaccines, a part of the pathogen important for its survival and causing infection or the whole organism is administered in the body. The part of the pathogen (or the whole) against which the immune system elicits response is called the antigen.

The USA was using quadrivalent flu vaccines since 2013-2014 season. But, this year it will shift to the trivalent one after the recommendation of WHO in September last year and recent approval of USFDA. The trivalent vaccine will exclude the B/Yamagata lineage and will contain vaccine viruses or viral proteins from two A type viruses (H1N1 and H3N2) and one B/Victoria lineage.

The Indian scenario

India has not been on back foot in vaccinations, including the flu vaccines. During the 2009 swine flu pandemic, India developed its own vaccines against it.

The Serum Institute of India (SII) launched its intranasal H1N1 vaccine in July 2010 under the brand name Nasovac. Again in the same year, Bharat Biotech launched another vaccine named HNVAC in October. The biotech firm claimed that it was India’s first indigenously developed vaccine against the flu pandemic virus. The HNVAC was developed using cell culture, which was the only manufacturing process then, claimed by Bharat Biotech. The SII nasal vaccine used egg-based manufacturing of the vaccine. Notably, India launched the first vaccine against general influenza in 2010.

When United States has decided to go for trivalent flu vaccine dropping B/Yamagata, India is going for quadrivalent vaccine. The (NCDC) National Center for Disease Control has released recommended composition for influenza vaccine for the season of 2024. It suggests that India will use Southern hemisphere 2024 quadrivalent vaccine as recommended by WHO, which will include the B/Yamagata lineage.