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By Gary Evans, Medical Writer
With researchers in Canada reporting that the current influenza vaccine has only 17% efficacy against the predominant H3N2 A strain, a historically bad flu outbreak continues in the United States.
The Centers for Disease Control and Prevention is bracing the public for its interim vaccine efficacy estimate, which is expected to be released in the next few weeks.
“I think it’s important to say that we expect that the effectiveness against the H3N2 strains will be low,” Anne Schuchat, MD, acting CDC director, said at a Feb. 2 press conference.
The CDC had previously projected a vaccine efficacy of around 30%, but a sobering report by Canadian researchers of a meager 17% efficacy has tempered any optimism.
The 17% figure “is less than half that reported for the same A(H3N2) vaccine in 2016-17,” the researchers noted. “Our 2017-18 interim vaccine efficacy (VE) for influenza A(H3N2) is more comparable to the 2017 southern hemisphere interim VE of 10% reported from Australia.”
Flu seasons dominated by H3N2 can be particularly deadly, and comparison with past seasons suggests a heavy toll will be taken in the final counting for this season.
“The H3N2 years are the ones that have the higher number of deaths, and that upper level is about 56,000 for the total year,” said Dan Jernigan, MD, director of the CDC’s influenza division.
In a CDC surveillance system that includes 2,800 physician offices and emergency departments, 7.1% of patients were reporting with flu-like illness.
“We’ve had two seasons in the last 15 years that were higher than that,” he said. “The first was the 2009 H1N1 pandemic, which peaked at 7.8% and the [other was the] 2003-2004 season — a high severity H3N2 season — which peaked at 7.6%.”
For more on this story, see the March 2018 issue of Hospital Infection Control & Prevention.