As expected, this year's flu vaccine looks like it's pretty much of a dud.
The vaccine only appears to cut the chances that someone will end up sick with the flu by 23 percent, according to the first estimate of the vaccine's effectiveness by the federal Centers for Disease Control and Prevention.
The CDC had predicted this year's vaccine wouldn't work very well because the main strain of the flu virus that's circulating this year, known as an H3N2 virus, mutated slightly after the vaccine was created. That enables the virus to evade the immune system response created by getting vaccinated.
The effectiveness of the flu vaccine varies dramatically from year to year, but can be as high as 50 percent to 60 percent, the CDC says. So if the early estimate of this year's vaccine's effectiveness, reported in this week's Morbidity and Mortality Weekly Report, holds up, it would put the protection at the low end.
Nevertheless, the CDC and others are still urging people to get their flu shots because the vaccine does appear to work well against other, less common strains of the virus that are circulating, and they could become more common as the flu season progresses. We're about halfway through.
"The flu season is not yet over," said William Schaffner, an infectious disease expert at Vanderbilt University. "There are other less impressive strains that are out there making people sick, and against those strains the vaccine is actually on target. So it's providing partial protection."
The CDC has been predicting that this year could be a bad year for the flu because of the expectation that the vaccine wouldn't work very well and because H3N2 viruses tend to be pretty nasty. So the CDC has been urging doctors to be more aggressive about using antiviral drugs like Tamiflu and Relenza when their patients get the flu, especially those at high risk for complications.
"Physicians should be aware that all hospitalized patients and all outpatients at high risk for serious complications should be treated as soon as possible with one of three available influenza antiviral medications if influenza is suspected, regardless of a patient's vaccination status and without waiting for confirmatory testing," the CDC's Joe Bresee said in a statement.
MELISSA BLOCK, HOST:
Today, the Centers for Disease Control and Prevention released its first estimate of the effectiveness of this year's flu vaccine, and the news isn't good. As NPR's Rob Stein reports, the estimate confirms fears that this year's flu shots aren't working very well.
ROB STEIN, BYLINE: The CDC's been warning for weeks that this year's flu shot was probably going to be pretty lame. And so far that prediction seems to be coming true. Alicia Fry, a CDC epidemiologist, says the vaccine looks like it's only about 23 percent effective.
ALICIA FRY: What this means is that if you were vaccinated your chances of getting a flu illness that required you to go to the doctor was reduced by 23 percent.
STEIN: That's less than half as effective as the flu shot can be. So why is the vaccine turning out to be such a dud? Blame the main strain of flu viruses that are out there this year. It mutated slightly since the vaccine was produced, so the vaccine's not revving up the immune system enough to fight it off very well.
FRY: The viruses that are circulating in the majority of the country have changed genetically enough that we would expect the vaccine not to be as effective.
STEIN: And this comes at a particularly bad time. That strain that mutated is what scientists call an H3N2 virus, and H3N2 flu viruses tend to be nasty, making more people sick, sending more to the hospital and killing more people than other strains, especially kids and older people. So a lot of you might be thinking - why did I bother getting my flu shot? Or if you haven't gotten one yet - I might as well skip it this year. Fry says nope, it's still worth it. That's because the vaccine does protect a least a little against that nasty H3N2 virus and is working pretty well against other less common strains that are out there and could get more common later this year.
FRY: In almost every flu season another flu virus circulates, and we would expect the vaccine to continue to be effective against other viruses other than the H3N2.
STEIN: All this does highlight some big problems with making the flu vaccine. First of all, because the virus changes every year, scientists have to make a new vaccine every year. And scientists have to make an educated guess, months before every flu season begins, which strains of the flu the vaccine should try to protect people against. So William Schaffner, of Vanderbilt University, says researchers are working hard to come up with a better way so the vaccine won't be such a gamble every year.
WILLIAM SCHAFFNER: So the holy grail of influenza vaccine researchers is what's called a universal flu vaccine, one that would protect against all these variant strains, and maybe one that we only would have to get ourselves every five years or maybe only every 10 years. That would be a boon.
STEIN: But that's still years away from becoming a reality. So, in the meantime, the CDC says continue getting your flu shots, and if you do get the flu anyway, go see your doctor right away to see if you can get some antiviral drugs. Rob Stein, NPR News. Transcript provided by NPR, Copyright NPR.