Flu Vaccine a Pretty Good Match for Viruses This Year: CDC

It's not perfect, but this year's flu vaccine is a fairly good match for the circulating viruses, U.S. health officials reported Thursday.

Overall, the vaccine is 48 percent effective. For the predominant circulating influenza A type H3N2 flu strain, its effectiveness comes in at 43 percent. But it's 73 percent effective against influenza B viruses, according to the U.S. Centers for Disease Control and Prevention.

"The effectiveness is a little bit lower than we would like to see, but it's similar to what we have seen for H3 viruses when the vaccine is a good match for what's circulating," said Brendan Flannery, a CDC epidemiologist.

Indications are that infections are still rising in certain regions of the country, like the Midwest, but declining in others, like the Northwest.

This is shaping up as a moderately severe flu season, he added.

In similar seasons, about 60,000 hospitalizations and about 2,000 deaths were prevented with vaccine effectiveness at about 45 percent, Flannery said.

"So, there are a lot of hospitalizations and deaths prevented when the vaccine is not as perfect as we would like," he noted.

The effectiveness of the vaccine is less than hoped because the H3N2 virus is able to mutate, Flannery explained.

While 40 percent to 50 percent effectiveness may not sound like much, when spread across an entire population, the effect is significant, he said.

"A 50 percent reduction in doctors' visits for flu means less time off work or taking care of a child who is not in school," Flannery said. "A 50 percent reduction in doctors' visits may translate to a similar or greater reduction in more severe outcomes like hospitalizations and complications of flu."

If vaccination prevents half of influenza illnesses across all age groups, "that's a big difference in the number of hospitalizations or deaths in a season like this one -- that's a big deal," Flannery said.

These findings were based on data from more than 3,100 children and adults with acute respiratory illness seen during Nov. 28, 2016, to Feb. 4, 2017, at five sites with outpatient clinics in the United States.

Flannery also urged people who come down with flu to get treated with antivirals when there's risk of severe disease. "Antivirals shouldn't be withheld pending influenza testing or based on whether you were vaccinated or not," he said.

The report was published Feb. 17 in the CDC's Morbidity and Mortality Weekly Report (MMWR).

Dr. Amesh Adalja is an affiliated scholar at Johns Hopkins University Center for Health Security in Baltimore.

"The current flu vaccine is the best preventative measure we currently have. But, the lack of high levels of protection conferred by vaccination underscores the need for new vaccines that provide substantially higher protection as the flu burden remains sizable, even with high levels of vaccination," Adalja said.

According to another report in this week's MMWR, influenza activity continues to increase in some parts of the country.

Influenza A type H3N2 is the predominant strain, said Lynnette Brammer, a CDC epidemiologist and co-author of the report.

"As you would expect in an H3N2 year, we are seeing more severe disease in people 65 and older and increasing rates of hospitalizations and deaths," she said.

Brammer added that folks aren't out of the woods yet. "The season hasn't peaked yet, and we don't know when the peak is going to happen," she said.

The CDC still recommends that people get vaccinated, and "if they get sick there are antiviral drugs that can help prevent severe complications, particularly for people at high risk or [who] have severe or progressive illness," Brammer said.

Dr. Louis Morledge, an internist at Lenox Hill Hospital in New York City, agreed that it's still worthwhile to get a flu shot.

"The season hasn't peaked, so there is some effectiveness from getting vaccinated even through the end of March," he said.