So last year, when H3N2 (Influenza A virus) was the most common flu virus around, the vaccine shot was pretty lousy.
“If it’s an H1N1 year, then the vaccine is closer to 60 percent effective,” Jernigan said.
But what if it’s H3N2 again, like last season?
Treanor pointed out that this year’s flu vaccine contains the same strain of H3N2 as the 2016 vaccine, so if the new flu season is dominated by H3N2 again, it could be another bad season.
And what about the 2017-2018 flu season?
Last year’s shot was only 20 percent to 30 percent effective because it was grown in eggs, according to the authors of a new report.
The egg process is not unusual. But a mutation in the predominant flu virus, called “Influenza A” or chemically known as H3N2, limited the vaccine’s potency, said study co-author Dr. John Treanor.
When H3N2 comes in contact with eggs, it changes, making it different from the virus that’s circulating, he and his colleagues explained.
Growing influenza virus in eggs, then inactivating it and purifying it is the traditional method. “But there are some downsides to using chicken eggs as the production material,” Treanor noted.
Two new methods of producing vaccines are being tried
One approach — using animal cells as the production material — allows the use of more standardized methods.
“Another approach is to use DNA techniques and to synthesize the vaccine directly from the genetic sequence of the virus,” Treanor said.
Both these methods — cell culture (Flucelvax) and DNA (Flublok) – are licensed by the FDA.
Jernigan said that these new technologies are used for the production of new vaccines. He cautioned, however, that it is not yet known if these methods produce a more effective flu vaccine than using eggs.
Flu vaccines work by inducing the body’s immune system to make antibodies against proteins found in the outer layer of the flu virus to kill it.
A mutation in the H3N2 virus several years ago led to the current circulating strain.
The 2016-2017 flu vaccine was updated to include the new version of the H3N2 protein. But Treanor’s team found that this new version also mutated when grown in eggs.
Their research showed that antibodies from ferrets and humans exposed to last year’s egg-based vaccine did a poor job of killing the H3N2 virus.
But when they tried a non-egg-based vaccine, they found the resulting antibodies were better able to kill the new H3N2 virus.
Jernigan said the goal is to find a universal long-lasting flu vaccine.
Each year up to 60,000 Americans die from flu and hundreds of thousands are hospitalized, he said.
“Even though flu vaccine isn’t perfect, getting a flu shot is still the best way to protect yourself from the flu,” Jernigan advised.
What are factors that influence how well the vaccine works?
How well the flu vaccine works (or its ability to prevent flu illness) can range widely from season to season. The vaccine’s effectiveness also can vary depending on who is being vaccinated. At least two factors play an important role in determining the likelihood that flu shot will protect a person from flu illness: 1) characteristics of the person being vaccinated (such as their age and health), and 2) the similarity or “match” between the flu viruses the flu antidote is designed to protect against and the flu viruses spreading in the community.
During years when the flu vaccine is not well matched to circulating influenza viruses, it is possible that no benefit from flu vaccination may be observed. During years when there is a good match between the flu vaccine and circulating viruses, it is possible to measure substantial benefits from flu vaccination in terms of preventing flu illness.
However, even during years when the flu shot match is good, the benefits of flu vaccination will vary, depending on various factors like the characteristics of the person being vaccinated, what influenza viruses are circulating that season and even, potentially, which flu vaccine was used.