Flu vaccines have reduced the likelihood of acute illness by 36% so far this year, the CDC says in an interim report, a number much better than previously predicted. But shots made using a cell-based process, rather than the far more common egg-based method, appeared to be more effective, triggering more interest in studying the differences between the two.
This year's vaccines were only 25% effective against H3N2 viruses—the predominant strain that tends to cause more severe illness. An unsatisfactory number, yes, but it’s better than interim estimates of 17% from Canada and 10% from Australia, the CDC said.
Vaccine effectiveness hit a low of 19% during the 2014-15 flu season, when the circulating strains of the virus didn't match up with those included in vaccines. But this season, new questions arose about the widely adopted egg-based vaccine production process, which was suspected to have reduced the shots' effectiveness, according to a recent New England Journal of Medicine commentary.
“[G]enetic changes in the vaccine virus hemagglutinin protein that arise during passage in eggs might result in a vaccine immune response that is less effective against circulating viruses,” says the CDC report.
FDA Commissioner Scott Gottlieb, M.D., said in a statement that a preliminary analysis of data from the Centers for Medicare & Medicaid Services indicates that the cell-based flu vaccine “appears to have somewhat better effectiveness” than the egg-based vaccine.
“Scientists at the FDA, CDC, and NIH are working diligently to fully understand the basis for this finding, so that all of next year’s vaccines can provide better protection in preventing the flu,” said Gottlieb. An FDA expert panel will convene in two weeks to help select strains for next season’s flu vaccines, he said.
Flu activity has been particularly strong this year, having led to the deaths of at least 84 children, the CDC reported.
Researchers based the midterm report on data from 4,562 children and adults through Feb. 3. However, the CDC found that this year's vaccines fared better among children; the agency estimates that they’re 59% effective against H3N2 among children aged 6 months to 8 years.
The problems noted with seasonal vaccines have drawn renewed interest in developing a universal flu vaccine that can cover many strains for many seasons. Sanofi Pasteur, Johnson & Johnson, BiondVax, FluGen and Vaccitech are among the companies working on universal vaccines, but Gottlieb admitted that it will still take several years before one of them could win an FDA approval.
In the meantime, Gottlieb said the FDA is interested in cell-based and recombinant vaccines, which could be manufactured more quickly than egg-based varieties, giving scientists “more agility in responding to changes in influenza strains.”