CDC: Flu vaccines just 25% effective against worst strain this year

This year's vaccines reduce flu cases by about one third, but effectiveness against the most common strain causing the most misery is lower.

This year’s flu vaccines reduce the chance of getting the flu by about one third, but are just 25% effective against the nasty strain causing the most misery, according to preliminary estimates released Thursday.

The findings, published by the Centers for Disease Control and Prevention (CDC), come as no surprise to flu experts tracking the worst influenza season in a decade.

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In a typical season, vaccines prevent 40% to 60% of flu cases serious enough to send people to doctors’ offices. This year, vaccines are preventing 36% of those illnesses, the new report said. But they are preventing just 25% of illnesses caused by a type of influenza A called H3N2. That strain, which always poses a vaccine challenge, is behind three quarters of verified flu cases so far this season, CDC said.

Flu experts were quick to say the vaccines remain worthwhile.

“We’ve got a good vaccine but not a great vaccine. It is modestly effective,” said Arnold Monto, a professor of epidemiology at the University of Michigan and a co-author of the report. The report is based on data from 4,562 patients, including some from Michigan.

Monto noted that the 25% effectiveness against H3N2 is higher than the 10% reported earlier from Australia. Canadian researchers estimated a 17% effectiveness rate. All the numbers come with statistical hedging: because they are based on fairly small groups of patients, the real numbers could be somewhat higher or lower.

In any case, this year does not appear to be the worst recent year for overall vaccine effectiveness. That would be 2014-2015, when the CDC reported a 19% flu prevention rate and blamed a mismatch between the strains in the vaccine and the ones causing illness.

Totally preventing flu is not the only goal of vaccination: it can also reduce the severity of flu symptoms for people who do get sick, Monto said.

In a year in which more than 50,000 Americans may die of flu, and 63 child deaths have already been reported, even imperfect vaccines are valuable, said Aaron Glatt, chairman of the department of medicine at South Nassau Communities Hospital, Oceanside, New York. He is a spokesperson for the Infectious Diseases Society of America.

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It has is a huge lifesaving effectiveness for a certain number of patients,” he said. He noted that about 70% of children who have died of flu in recent years were not vaccinated, according to data published this week.

Still, the need for better flu vaccines is clear, experts said.

“What we need are new approaches to vaccination,” including, eventually, a universal vaccine that protects against all strains, for multiple years, Monto said. More potent yearly vaccines could make it through the pipeline sooner, he said.

Scientists also need to take a closer look at differing performance among vaccines already on the market, said Richard Webby, an infectious disease researcher at St. Jude Children’s Research Hospital, Memphis. There are some indications, he said, that some vaccine production techniques produce better H3N2 protection than others do. But researchers do not have the data they need to recommend one vaccine over another.