Flu season is stirring up more than unpleasant symptoms as it begins its move across the United States. It’s also raising questions about the effectiveness of this year’s vaccine.
Experts warn that this year’s vaccine could be only 10 percent effective against a strain of the virus H3N2 that is expected to predominantly circulate in the United States. That warning, as published late last month in the New England Journal of Medicine, is based on a preliminary analysis of the flu season in Australia.
Experts warn that this year’s flu vaccine could be only 10 percent effective against the H3N2 strain of the virus.
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Flu vaccines distributed there have the same composition as those being distributed in the United States. Researchers often look to the southern hemisphere for hints of what’s in store locally.
But that 10 percent figure isn’t to say that vaccine holdouts should forgo the flu shot this season.
“If it lessens the severity by 10 percent, that makes a big difference,” said Dr. Matt Roth, medical director for ProMedica Wellness.
The physician explained that there are two factors that account for year-to-year fluctuations in the effectiveness of the flu vaccine, which typically reduces the risk of illness by 40 percent to 60 percent in the overall population, according to the Centers for Disease Control and Prevention.
The first factor, which Dr. Roth said is not at play this year, is a mismatch between the strain of the virus that the vaccine protects against and the strain that circulates during flu season. Because the composition of flu vaccines is decided months before flu season, to allow for distribution time, there’s naturally some guesswork involved.
The New England Journal of Medicine points to the 2014-15 flu season as an example of this mismatch, noting that more than 80 percent of the circulating H3N2 viruses that year differed from those strains protected against in the vaccine. Effectiveness against the most prevalent strain that season was just 13 percent.
The second factor reflects tiny changes that the influenza virus undergoes while a vaccine is being created; that process takes place in eggs. These changes affect the vaccine’s ability to combat even a strain that is a match, which Dr. Roth and Dr. Tanyanyiwa Chinyadza, an infectious disease consultant with Mercy Health, said is a factor in this year’s vaccine.
“It may be in the way, or the technique, that we make the vaccine,” said Dr. Chinyadza.
He noted that these and other factors mean that the flu vaccine will never be 100 percent effective; 50 percent to 70 percent effectiveness is considered a good year.
The CDC puts the overall effectiveness rate of the vaccine last year at 42 percent; in the 2015-16 season at 48 percent; in the 2014-2015 season at 19 percent overall (exempting the most prevalent strain, which not everyone contracted), and in the 2013-14 season at 52 percent.
So are Americans are in for a particularly severe flu season?
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“That’s the concern, especially if the rest of the people decide not to get their flu shot,” Dr. Roth said, noting that even if this year’s 10 percent estimate proves accurate, the vaccine can still lessen the severity of symptoms, shorten the duration of the illness, and help control the spread of the virus.
Because the 10 percent estimate applies only to a particular strain of the virus, the vaccine is also expected to better protect against other strains that will additionally circulate this year.
The southern hemisphere flu season is usually a good predictor of the northern hemisphere flu season, Dr. Chinyadza said, so a higher-than-usual incidence of influenza in Australia this year could mean a more severe season in the United States. He, too, recommended a vaccine.
“It’s not going to hurt you,” he said. “You can only gain from it.”
It’s also worth noting that it’s still relatively early in flu season, which generally runs October to May. Influenza is currently classified as “widespread” in four states, according to the CDC, with activity in Ohio sitting at “local” and activity in Michigan sitting at “sporadic.”
That’s in line with where both states were at this time last year, according to the CDC, although no states reported widespread activity last year until late December.
Spokeswoman Shannon Lands said the Lucas County Health Department has documented seven flu-related hospitalizations this year, compared to two by this point in 2016 and five in 2015.
“It's not like we're seeing a dramatic increase,” she said. “Maybe just a few more than last year.”
In addition to a vaccine, Dr. Roth and Dr. Chinyadza each recommend proper hand hygiene as a means of keeping the flu at bay this season. And if you begin to feel a fever, cough, or body aches, Dr. Roth added, it’s best to stay home.
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