Friday 6 February 2015

Press release: Flu vaccine shows low effectiveness against the main circulating strain seen so far this season

Press release: Flu vaccine shows low effectiveness against the main circulating strain seen so far this season New research from 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 are 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.


This 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.

PHE has carefully examined some of the influenza A(H3N2) viruses circulating this season by antigenic and genetic analysis, and has found evidence of drift compared to the A(H3N2) virus strain in the flu vaccine. The low vaccine effectiveness that has been found shows that this drift has been significant and resulted in a mismatch to the vaccine strain.

The UK findings follow the recent publication of the US and Canada’s mid-season vaccine effectiveness estimates, both of which also revealed the vaccine had unfortunately provided little protection against circulating A(H3N2) viruses this season in these countries. This was also linked to drift observed in H3N2 viruses. Public Health England

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