Adjuvanted pandemic flu vaccine efficacious in children and young adults

Andrews N. J Infect Dis. 2011;203:32-39.

An oil-in-water adjuvanted pandemic (H1N1) 2009 vaccine demonstrated high vaccine efficacy in children and young adults in England, according to researchers from the Health Protection Agency Centre for Infections in London.

The vaccine, however, was not as effective in adults aged 25 years and older — in whom the vaccine efficacy was only 27% — 14 days after vaccination. In those aged younger than 25 years, the vaccine efficacy was 89%.

The researchers collected data from 933 patients, defined as those with laboratory-confirmed pandemic (H1N1) infection, and from 1,220 controls, who presented with flu-like symptoms but tested negative for pandemic (H1N1) infection. All of the patients and controls presented to their general practitioner or the hospital with symptoms from November 2009 to January 2010, when England was experiencing the second wave of the 2009 pandemic. The vaccine was available in October 2009, and the starting date of Nov. 1, 2009, marks the earliest possible date that an individual would have derived protection from the vaccine.

Among the patients, 31 had received the adjuvanted pandemic (H1N1) 2009 vaccine. Among the controls, 76 had received the vaccine. Overall, the vaccine efficacy from 14 or more days after vaccination was 62%. The vaccine efficacy in children younger than 10 years was 77%. In those aged 10 to 24 years, the vaccine efficacy was 100%. In those aged 25 to 49 years, the vaccine efficacy was 22%. In those aged 50 years and older, the vaccine efficacy was 41%.

At this point, researchers are simply laying out hypotheses as to why the efficacy of the vaccine was different in the various age groups, and there really are no definitive data to back up these hypotheses. The interesting thing in this article is that it only took one vaccination to protect children younger than 10. The reason why this did not do as well in older people is all conjecture. Adjuvanted vaccines are useful in a pandemic because you can make more vaccine doses quickly, since it doesn’t take as much virus per dose. Adjuvanted vaccines have also been shown in some studies to be more effective in immunocompromised patients, like cancer patients. The problem with adjuvanted influenza vaccines, however, is that they have not been studied anywhere near as long as unadjuvanted vaccines.

—Jon Abramson, MD
Professor of Pediatrics, Wake Forest University

Disclosure: Dr. Abramson reports no relevant financial disclosures.

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