Seasonal influenza vaccination programmes are underway across Europe, with at risk groups – such as older people and pregnant women – first in line to receive the new vaccine.
The viruses that cause the flu evolve rapidly so the composition of the vaccine must change every year too. That’s why even those vaccinated last year still need to be immunised.
This year, the vaccine protects against the three most common forms of flu, including the H1N1 virus which caused the 2009 flu pandemic.
The composition of the vaccine is worked out every year by experts at the World Health Organisation (WHO). The WHO recommendation is usually taken up by health authorities across the world.
Prof Bruno Lina, Professor of Virology at the University of Lyon, said national reference centres play a key role in determining the make-up of the vaccine.
“Flu is one of the most studied viruses in the world. Information from national reference centres across the globe feeds into the final decision. Using this network we collect data giving clear picture of which viruses responsible for most of the flu cases,” he told Vaccines Today.
Prof Lina said changes to the composition of the virus are necessary because influenza can quickly transform itself in order to evade the body’s defences.
“The body builds up immunity to viruses but influenza is an RNA virus meaning it can adapt itself and escape the immune response. The viruses can change proteins in a way that makes it difficult for the body to recognise them,” he said.
“So, if you want to protect people you need to have an optimised vaccine that contains the latest viruses that are circulating.”
Two winters, two vaccines
The WHO consults its network of influenza surveillance centres twice a year – once to help decide on the composition of the vaccine for the northern hemisphere, and once to decide on which viruses people need protection against in the southern hemisphere.
The seasonal vaccines given north and south of the equator are usually similar but can to differ slightly given the pace with which flu viruses mutate.
“We are always six months behind the evolution of flu viruses. For seasonal flu in the northern hemisphere in 2010, it was decided in February which three viruses would be included in the trivalent vaccine,” according to Prof Lina.
“Every six months we have an opportunity to change the composition of the seasonal influenza vaccine. Sometimes there are no changes – this year the northern hemisphere and southern hemisphere vaccines are identical – but other times new strains emerge which must be included,” he added.
The arms race between scientists and the flu virus looks set to continue, with experts having to stay on their toes to keep up with a versatile group of viruses.
Last update: April 10, 2017, by Gary Finnegan