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25-10-2011 | General practice | Article

Doubts over flu vaccine efficacy


Lancet Infect Dis

2011; Advance online publication

The effectiveness of influenza vaccines remains unclear, particularly in high-risk groups, conclude US researchers.

They say that numerous studies looking at non-specific outcomes such as all-cause death and influenza-like illness may have led to overestimation of the specific benefits of flu vaccination, and call for increased efforts to develop improved vaccines.

As reported in The Lancet Infectious Diseases, Professor Michael Osterholm (University of Minnesota) and team sought to quantify the benefits of flu vaccines licensed in the USA. They identified 31 studies evaluating vaccines, including 17 randomised controlled trials, in which influenza infection was confirmed using specific laboratory diagnostic tests.

Pooled analysis indicated that the trivalent inactive vaccine (TIV) showed only 59% efficacy against seasonal flu in adults aged 18-65 years. And the monovalent pandemic vaccine was effective against swine flu in just 69% of individuals, which the authors say "is not adequate for a pandemic setting where the antigen match is ideal and antigen drift has not occurred".

Live attenuated influenza vaccine (LAIV) showed relatively high protection against influenza in young children, however, preventing infection in 83% of children aged 6 months to 7 years. But the authors say they found no eligible trials of TIV in people aged 65 years or older or in children aged 2-17 years, nor of LAIV in individuals 8-59 years.

"Evidence for consistent high-level protection is elusive for the present generation of vaccines, especially in individuals at risk of medical complications or those aged 65 years or older," write Osterholm and colleagues.

"The ongoing health burden caused by seasonal influenza and the potential global effect of a severe pandemic suggests an urgent need for a new generation of more highly effective and cross-protective vaccines that can be manufactured rapidly."

GP News is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2011

By Caroline Price