Flu vaccine remains effective as mutated strain drives early spread

The flu vaccine appears to be providing ‘strong’ protection against severe illness despite the emergence of mutated strain behind the early spread of the virus this season.

UK Health Security Agency officials published data that the flu vaccine is currently 70-75% effective at preventing hospital attendance in children aged 2 to 17 years and 30-40% effective in adults.

While protection varies from year to year, depending on the strains circulating, it is typically between 30-60% with higher effectiveness seen in younger age groups, UKHSA said.

The flu season has got off to an ‘unusually early start’ this year, with mutations to the circulating influenza A(H3N2) strain thought to be responsible.

UKHSA also confirmed that a drifted influenza A(H3N2) strain, called subclade K, currently dominates cases in England.

Experts said the mutations seen in the circulating H3N2 strain is thought to have increased the reproduction number from 1.2 to 1.4 which means that every 100 people with flu can infect 140 people rather than 110 to 120 people in other flu seasons.

UKHSA said the protection levels seen in children so far – the age group currently driving the spread of flu – is ‘particularly encouraging’.

High effectiveness in younger age groups may also provide indirect protection to other groups through reduced transmission, the Agency added.

The NHS had already warned the NHS was in for a ‘long and drawn out winter’ after signs from Australia which has just had its biggest ever flu season.

Japan has also declared a flu epidemic, with many schools needing to close.

Those with long-term conditions have been urged to take up the offer of a vaccine after less than 30% have had their jab so far.

Dr Jamie Lopez Bernal, consultant epidemiologist for immunisation at UKHSA, said: ‘These results provide reassuring evidence that this season’s flu vaccines currently offer important protection to children and adults, despite concerns about the new subclade.

‘The high vaccine effectiveness in children strengthens the case for ensuring all eligible young people get vaccinated. When more children are protected, it helps stop the spread of flu to others around them.’

Dr Mary Ramsay, director of public health programmes at UKHSA added: ‘Strains can fluctuate throughout the season causing different waves and those more prevalent earlier may change as winter progresses.

‘The flu vaccine has a number of components protecting against the three main flu virus types and it typically provides protection against severe clinical disease even when ‘drifted’ strains are seen.’

Professor Adam Finn, professor of paediatrics at the University of Bristol, said the H3N2 strain appeared to have acquired several new mutations over the summer and was responsible for many of the flu cases now being seen.

The early start is worrying because there has not been enough time yet for a lot of people to get vaccinated, he added.

‘Usually, November is a month when a lot of people get the vaccine before the infections start to spread in December and January.

‘The bottom line is that it’s looking possible that we may be facing a very bad flu season this year and the best thing we can all do right now to tackle the problem is to get vaccinated.’