Research shows that flu vaccine efficacy measures could be wrong

According to research from the University of Michigan, a particular measure of flu vaccine efficacy that has been used for a number of past controlled trials is not accurate, leading to overselling the protection the vaccines provide.

Joshua G. Petrie and his colleagues showed that using serologic measures to determine vaccine efficacy can lead to the overestimation of protection. They also found that virus isolation in a cell culture was not very accurate as it can lead to missed cases, CIDRAP News reports.

The most effective tool for determining vaccine efficacy was real-time polymerase chain reaction. During their trial, this method was determined to be about 70 percent accurate.

“That may suggest that we should lower the usual description of vaccine efficacy from 70 percent - 90 percent, in healthy adults closer to 70 percent; however, further confirmation by other studies is desirable,” the report said, according to CIDRAP reports.

The main reason that serologic measures may overestimate efficacy is because of what is called the “antibody ceiling.” This is the idea that once antibody titers increase when responding to a vaccine, they are unable to rise higher in response to the actual infection. This would mean that infections in vaccinated people would go unidentified.

"I agree with [the authors'] conclusion but primarily because RT-PCR is a great 'equalizer' for all sites, since RT-PCR should carry about the same sensitivity and specificity at each site, provided the expertise is there to prevent false-positives," Robert B. Couch, a vaccine expert at Baylor College of Medicine in Houston, said by e-mail, CIDRAP News reports. "This will expand the number of sites that can do good sensitivity testing for influenza infections and vaccine evaluations. Most labs doing such testing lack expertise in flu methods, as most only do HAI tests for serology and isolation tests in a general lab or other non-flu-experienced location. For these, RT-PCR testing is superior."