CIDRAP study shows lower-than-touted flu vaccine efficacy

Oct 25, 2011 – The efficacy of seasonal influenza vaccine appears to be lower than the 70% to 90% figure often cited, according to a study led by researchers from CIDRAP published today in The Lancet Infectious Diseases.

CIDRAP Director Michael Osterholm, PhD, MPH; Preparedness Program Coordinator Nicholas Kelley, PhD; and colleagues conducted a meta-analysis that showed the efficacy of the trivalent inactivated vaccine (TIV) in adults 18 to 65 to be 59%, while the nasal spray vaccine showed an efficacy of 83% in young children.

It also raised questions about the evidence for the effectiveness of influenza vaccines in elderly people and, for certain types of vaccines, in children and younger adults as well.

However, Osterholm was quick to point out that the flu vaccine is still a good vaccine and should continue to be administered. "The clear message we've sent here is to continue to use this vaccine," he told CIDRAP News. "Our data strongly support that there can be a moderate level of protection from influenza vaccines," he said. "As an intervention goes, that's still an important level of protection."

Besides Osterholm and Kelley, other study authors were Alfred Sommer, MD, MHS, of the Johns Hopkins Bloomberg School of Public Health in Baltimore, and Edward A. Belongia, MD, of the Marshfield Clinic Research Foundation in Marshfield, Wis. The study was funded by the Alfred P. Sloan Foundation.

The team conducted a rigorous analysis of 44 years' worth of studies and applied very strict criteria to filter out potential bias and confounding. They sifted more than 5,000 studies and found only 31 that they felt provided reliable evidence about the efficacy and effectiveness of flu vaccines.

Overall, the researchers found that existing flu vaccines can provide moderate protection from laboratory-confirmed flu, but protection is much lower in some groups and during some seasons.

Pooled evidence from randomized controlled trials (RCTs) showed that standard TIVs had an efficacy of 59% in young adults (18 to 65), but the authors found no RCTs demonstrating TIV efficacy in adults 65 and older or children aged 2 to 17.

For the live attenuated flu vaccine—the nasal spray version—evidence from 10 RCTs showed 83% efficacy in children 6 months to 7 years old, but no RCTs supported its efficacy in older children or adults.

The authors' main conclusion is that, while existing flu vaccines should continue to be used, better ones are needed.

See also:

Oct 25 Lancet Infect Dis study abstract

Oct 25 CIDRAP News story "Strict meta-analysis raises questions about flu vaccine efficacy"

Oct 25 CIDRAP News story "Public health groups say flu vaccine is best tool, despite limitations"

Lancet Infect Dis podcast interview with Dr. Osterholm