The influenza vaccine chosen for this year’s immunisation campaign shows low effectiveness against the main circulating strain seen so far this season, public health officials have admitted.
Research by Public Health England has found that the seasonal influenza vaccine has provided low protection this winter against flu infection caused by one particular subtype, H3N2.
This is because of a mismatch between the A(H3N2) strain selected for the vaccine this year and the main A(H3N2) strain that has been circulating in the UK this winter.
The findings on mid-season flu vaccine effectiveness in the UK were published today in Eurosurveillence.
The research, based on the results from 1,314 patients presenting in primary care across the UK, found that vaccine effectiveness in preventing laboratory confirmed influenza was estimated to be 3% overall.
This compares to approximately 50% vaccine effectiveness that has typically been seen in the UK over recent years.
“If a change in the virus is detected once production has started it is not possible to change it”
The current flu season has been dominated by circulation of influenza A(H3N2) subtype viruses, which cause particular problems for vulnerable groups such as the elderly and has resulted in care home outbreaks, hospitalisations and excess mortality in those over 65 years.
Antigenic and genetic analysis by PHE found evidence of “significant drift” compared to the virus strain in the flu vaccine, resulting in a mismatch between them.
The UK findings follow the recent publication of similar US and Canada’s mid-season vaccine effectiveness estimates.
Study author Dr Richard Pebody, PHE’s head of flu surveillance, said: “The World Health Organization monitors influenza globally and each year recommends the strains of flu virus that should be included in the flu vaccine for the forthcoming flu season.
“It takes from February through to August/September to produce sufficient quantities of the flu vaccine,” he said. “If a change in the virus is detected once production has started it is not possible to change it.
“The current vaccine is still expected to protect against flu A(H1N1)pdm09 and flu B – both of which may yet circulate this season, so anyone in an at-risk group should still get vaccinated if they have not already,” he added.
“Our findings also mean that the early use of antivirals to treat and help prevent serious cases of flu in vulnerable patients is even more important this season,” said Dr Pebody.
In recent weeks, there have been indications that influenza activity is stabilising. However, PHE said evidence of significant excess mortality, particularly in the elderly, continues to be seen, with more deaths than expected at this time of the year.
PHE’s weekly flu report was published today showed that levels of flu activity were at similar/lower levels than the previous week.