The vast majority of influenza vaccine doses are made from viruses grown in eggs, but that process can cause inconsistencies that make the vaccine less effective, and some experts are suggesting it's time to abandon the egg-based process altogether, Helen Branswell writes for STAT News.
How vaccines are grown in eggs
Ever since the advent of the flu vaccine, the vaccine has been grown in eggs. It's an inexpensive method that generally works, but according to Branswell it's not without its downsides.
The process begins when flu viruses are injected in hens' eggs, which provides a hospitable environment for them to multiply. But as they duplicate, the viruses are prone to mutations—mostly inconsequential tweaks, but occasionally, the mutations can affect the functioning of the vaccine.
After the viruses are weakened or killed and inserted into a vaccine, they serve as models of the flu virus used to "train" antibodies in how to defend the body, Branswell writes. But if the vaccine virus has mutated sufficiently, it may no longer serve as a good replica of the ordinary flu, and the vaccine may cease to be as effective.
In a study released in October, researchers reported that the poor performance of the flu vaccine during the 2016-2017 flu season was due to such a mutation.
Some experts believe that the best solution is to move away from egg-based vaccine production. "We need to do a lot to improve existing vaccines. And getting away from eggs would be very valuable," said Kanta Subbarao, the director of the World Health Organization's influenza collaborating center in Australia.
For more than a decade, the Biomedical Advanced Research and Development Authority (BARDA)—a U.S. government office tasked with preparing for public health emergencies—has worked with manufacturers to develop alternatives to egg-based production. So far, the effort has supported two non-egg-based vaccines: FluBlok and Flucelvax, which both are generated in insect cells.
Potential obstacles to abandoning the egg
But it may not be time to leave egg-based vaccines behind just yet, Branswell reports.
For one thing, Branswell writes there isn't much evidence that non-egg-based vaccines are any more effective than their egg-based kin. As such, manufacturers are hesitant to spend the money moving away from eggs, according to Branswell.
Further, a CDC official said manufacturers would need to apply for new regulatory licenses and conduct new costly trials, among other steps. "It's a pretty big manufacturing lift. Or at least regulatory lift," said Daniel Jernigan, the director of the CDC's influenza division.
Another obstacle is that many in the industry would prefer to focus on developing a long-term flu vaccine that can work across multiple flu seasons, rather than tweaking the production method on current, short-term vaccines, Branswell reports.
"In some ways, the whole discussion now about universal or game-changing vaccine has somewhat shifted the landscape," said Michael Osterholm, the director of the Center for Infectious Diseases Research and Policy at the University of Minnesota. "Because now people are going to say, 'Wait a minute. Am I going to invest in an intermediate stage of vaccine production … and do this kind of fix on the current vaccine as an intermediate stage or interim stage?'" (Branswell, STAT News, 11/7).
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