As the number of states reporting local flu activity has more than doubled since last week, researchers have found that egg-based influenza vaccine production may be yielding less effective vaccines.
The seasonal flu vaccine is most commonly given as the standard-dose trivalent flu shot which is made from virus components grown in eggs, but the results of a new study published in the journal PLOS Pathogens has shown that the egg-based vaccine offers a low level of protection against influenza A H3N2 viruses. The study, conducted by researchers at The Scripps Research Institute, has come out following findings that the seasonal influenza vaccine was about 42% effective at preventing illness during the 2016-2017 flu season.
The CDC notes that flu vaccine reduces the risk of becoming ill with the virus by 40% to 60%, and tends to be more effective for influenza A H1NA and influenza B viruses. That rate drops to 33% effectiveness for H3N2 viruses.
Using a high-resolution imaging technique, the researchers found that when grown in eggs, the H3N2 subtype mutates a key protein which allows the virus to better attach to receptors in bird cells. One mutation on the virus’s hemagglutinin glycoprotein, called L194P, prevents the human immune system from recognizing the virus surface’s main antibody target site and makes the vaccine less effective at triggering an immune response against H3N2 viruses. In addition, the researchers found that the H3N2 component currently included in the influenza vaccine has the mutation, explaining the lower level of protection offered against those circulating viruses.
“Now, we can explain—at an atomic level—why egg-based vaccine production is causing problems,” said the study’s first author, Nicholas Wu, PhD, calling for new vaccine production methods in a recent press release. As a result, he said, “There’s a huge need for flu vaccine research.”