How flu evolves to escape immunity

Washington – Researchers have discovered a new way  to improve future flu vaccines after finding that seasonal flu is able to escape immunity from vaccines with as little as a single amino acid substitution.

Additionally, they found these single amino acid changes occur at only seven places on its surface – not the 130 places previously believed.

The flu vaccine works by exposing the body to parts of inactivated flu from the three major different types of flu that infect humans, prompting the immune system to develop antibodies against these viruses. When exposed to the actual flu, these antibodies can eliminate the flu virus.

However, every two or three years the outer coat of seasonal flu (made up of amino acids) evolves, preventing antibodies that would fight the older strains of flu from recognising the new strain.

As a result, the new strain of virus escapes the immunity that has been acquired as a result of earlier infections or vaccinations.

For this study, Professor Derek Smith from the University of Cambridge, one of the two leaders of the research, together with Professor Ron Fouchier from Erasmus Medical Center in The Netherlands created viruses which had a variety of amino acid substitutions as well as different combinations of amino acid substitutions. They then tested these viruses to see which substitutions and combinations of substitutions caused new strains to develop.

They found that seasonal flu escapes immunity and develops into new strains typically by just a single amino acid substitution.

They also found that such single amino acid changes occurred at only seven places on its surface – all located near the receptor binding site (the area where the flu virus binds to and infects host cells). The location is significant because the virus would not change so close to the site unless it had to, as that area is important for the virus to conserve.

The research has been published in the journal Science.