Virus mutations may compromise immunity to H3N2 among middle-aged despite having antibodies

The researchers found that children between the age of 3-10 years had the highest neutralising antibody levels, while those in middle age had non-neutralising antibodies.

Myupchar September 14, 2020 15:12:01 IST
content powered by
Virus mutations may compromise immunity to H3N2 among middle-aged despite having antibodies

A recent study, conducted at the University of Pennsylvania School of Medicine, suggests that those born during the late 1960s and all of the 70s are in a permanent state of susceptibility to the H3N2 influenza virus as the antibodies (in those who have them) cannot protect them from the virus.

H3N2 is a type of swine influenza that was responsible for the flu pandemic in 1968. The pandemic had started from Hong Kong and spread quickly, at first throughout Asia and then to other continents. About one million people had died of the pandemic throughout the world and the USA had a high death and disease rate.

The study is published in the peer-reviewed journal Nature Communications.

Antigenic drift and shift

The influenza virus is an RNA virus. It rapidly mutates into new strains - one of the reasons why we have to get a new flu shot every year. The flu shot for a year provides you immunity against all the flu viruses predominant in that year.

Antigenic drift and shift are two ways a flu virus mutates.

There are two main antigens on the surface of the flu virus -- hemagglutinin (HA) and neuraminidase (NA). These antigens are what makes the name of a virus for example H3N2 or H1N1. Antigens are proteins on the surface of a pathogen that our immune system recognises and makes antibodies against.

Antigenic drift refers to small changes in these antigens that make a new strain of a given flu virus. For example 3C2.A is a strain of H3N2.

Antigenic shift, on the other hand, gives rise to new subtypes of a virus, say when two different types of flu virus interact. Flu pandemics usually occur because of an antigenic shift. The H3N2 virus had arisen when the H2N2 flu virus, responsible for the Asian flu pandemic of 1957-58, underwent an antigenic shift.

The study

The 3c2.A H3N2 viruses emerged during the 2014-15 flu season and remain one of the major circulating flu strains till date. Unlike the original H3N2 virus, the 3c2.A strains have a unique change in the HA antigen that hides a major site of the virus that our immune system uses to neutralise the virus.

For the study, the researchers conducted a serological survey in a US population. Serum samples collected before the 2017-18 flu season — from 140 children below the age of 17 and 212 adults between the age of 18 and 90 year — were included in the study. All the samples were tested for the presence of neutralizing and non-neutralising antibodies. Neutralising antibodies can prevent infection while non-neutralising antibodies only show up when an infection happens in the body.

The researchers found that children between the age of 3-10 years had the highest neutralising antibody levels, while those in middle age had non-neutralising antibodies.

The study indicated that this is because the new strains of the H3N2 virus have only non-neutralising epitopes conserved. Epitopes are exact locations on an antigen which antibodies recognise and bind to.

As per a news release by the University of Pennsylvania, exposure to a flu virus early in childhood provides long-lasting immunity against that virus. Since H3N2 showed up in 1968 and has been mutating ever since, the first age at which you encountered the virus would have a huge effect on how your immune system would react to the virus strains now.

“Most individuals born in the late 1960s and 1970s were immunologically imprinted with H3N2 viruses that are very different compared to contemporary H3N2 viruses. Upon infection with recent H3N2 viruses, these individuals tend to produce antibodies against regions that are conserved with older H3N2 strains and these types of antibodies typically do not prevent viral infections," said Dr Scott Hensley, the corresponding author of the study and Associate Professor of Microbiology at the University of Pennsylvania.

The research team suggested that it is possible that this absence of neutralising antibodies in the middle-aged people is why H3N2 is still prevailing in the human population. Also, more serosurveys should be done to better study the evolutionary trajectory of various strains of the flu virus and help in determining why flu vaccines work differently in people. It would also aid in designing better flu vaccines.

For more information, read our article on Influenza.

Health articles in Firstpost are written by myUpchar.com, India’s first and biggest resource for verified medical information. At myUpchar, researchers and journalists work with doctors to bring you information on all things health.

Updated Date:

also read

Dilip Kumar discharged from Mumbai hospital two days after pleural aspiration procedure
Entertainment

Dilip Kumar discharged from Mumbai hospital two days after pleural aspiration procedure

Dilip Kumar was initially supposed to be discharged on Thursday but the family and the doctors decided to let him rest in the medical facility for another day.

Explained: Why WHO's emergency usage listing is important for Bharat Biotech's COVAXIN
World

Explained: Why WHO's emergency usage listing is important for Bharat Biotech's COVAXIN

The European Union (EU), United Kingdom (UK) and Canada have not included COVAXIN in their approved list of vaccines as it has not been approved by the WHO

Why comedy is important in times of crisis: Humour serves a vital function during hardships
Arts & Culture

Why comedy is important in times of crisis: Humour serves a vital function during hardships

Our situation may not always be a laughing matter. But laughing itself matters, and when used appropriately, it can be one of our most effective coping mechanisms during a crisis.