Can You Get A Flu Shot And Still Get The Flu?

This year's flu season started about a month early, prompting federal health officials to warn it could be one of the worst in years. They're urging everyone to get their flu shots.

But like every flu season, there are lots of reports of people complaining that they got their shot but still got the flu. What's up with that?

Well, as Michael Jhung of the Centers for Disease Control and Prevention explains, there are lots of possible reasons.

The first is that while the flu vaccine is the best way to protect against the flu, it's far from perfect. In fact, the vaccine is only about 60 percent effective. So some people can get the flu even though they were vaccinated because the shot just didn't work for them.

The vaccine, for example, tends to work less well in the elderly. That's a big problem, since the elderly are among those at greatest risk for serious complications from the flu.

Another reason is that it takes about two weeks for the vaccine's protection to kick in. So if someone gets exposed to the flu in that time between when he gets the vaccine and when his immune system has responded sufficiently, he could still get sick.

Also, it's always possible that someone could get exposed to a strain of the flu virus that's not covered by the vaccine. This year's vaccine, though, looks like it should work pretty well — the flu virus strains in the vaccine appear to be a very good match for the most common flu strains that are circulating this year.

The last reason is that someone might get exposed to another kind of virus that causes symptoms that are very similar to the flu. There are lots of other viruses out there that can cause respiratory illnesses, such as adenoviruses, parainfluenza viruses and respiratory syncytial virus.

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Transcript

RENEE MONTAGNE, HOST:

Let's talk now about this year's flu season. The Centers for Disease Control warns that flu is spreading earlier than usual, and it's spreading fast. A least 18 children have died from the flu. The best protection is a flu shot, which is recommended even for young children. But experts say even that isn't a guarantee that you won't get sick.

To talk more about what makes this season different, we're joined by NPR health correspondent Rob Stein. Good morning.

ROB STEIN, BYLINE: Good morning, Renee.

MONTAGNE: So health officials are warning that this could be a particularly bad year. Why is that?

STEIN: Well, there's really two reasons. The first one is, as you mentioned, that it's a relatively early flu season. The flu hasn't gotten going this early in the season in about a decade - so, about a month ahead of time. And the second reason is one of the main strains that's circulating is what they call the H3N2 strain. And in past years, that's been particularly nasty. It's gotten a lot more people sick, and they've gotten much sicker and it's caused more deaths than usual.

MONTAGNE: For that reason, then, health officials are urging people to get their flu shots. I mean, it seems a little late, but I'm guessing it can still help.

STEIN: Yes, absolutely. The flu vaccine is definitely the best way to protect yourself from getting the flu. And there's plenty of vaccine out there, and there's definitely plenty of time to get vaccinated. It'll still protect people throughout the season. And this is especially important for people who are higher risk from the flu, and that includes the elderly, children and people with health problems. They're the ones that health officials really urge strongly to go out and get vaccinated as soon as possible. And the good news is, is that the vaccine so far seems like a pretty good match. It should be, hopefully, very protective against the strains that are circulating out there. There are three strains in the vaccine, and all three seem to be fairly closely matched with the predominant strains that are circulating. So that suggests that they should provide high protection for people against getting the flu this year.

MONTAGNE: Well, right, but, I mean, I know several people who've gotten really, really sick and have had gotten flu shots. Why is that?

STEIN: Right. There are several reasons why that could be: One is that even when the vaccine works, it's not 100 percent effective. In fact, it seems in past years, typically, it's about 60 percent effective. So even if you get a shot, it doesn't necessarily you're going to be completely protected. Another reason is that it takes about two weeks for the vaccine's protection to kick in. So if you get the shot, but then get exposed to the flu before the immunity has built up, then you still could get sick. And also, there are lots of other viruses that are out there circulating that cause symptoms that are very similar to the flu. There are viruses called adenoviruses and rhinoviruses. These are kind of bad cold viruses. The flu vaccine's not going to protect you against them at all. So if you get exposed to them, you're still going to get very sick. And also, there's also a possibility of other strains that are not covered by the vaccine.

MONTAGNE: What would be the advice for people if they do get sick?

STEIN: They should go to their doctor and get tested. And there are drugs out there - antiviral drugs like Tamiflu that can shorten the course of getting sick. It's usually the most effective if you start taking it within 48 hours of getting the flu. So it's important to get in there and get the drug soon. And it's not recommended for everybody, but it is definitely recommended for people who are at high-risk from the flu. And that tends to be elderly people, children, people with other health problems or people who are very sick or in the hospital with the flu.

MONTAGNE: And how much longer can we expect flu season to last?

STEIN: Yeah, that's a key question. Because it started so early, health officials are really wondering how long it's going to last. It could end up lasting as long as it typically does, into the late winter, early spring. In that case, it could end up being a more particularly severe season. Or it could end up petering out early, and it could end up being just a normal flu season, just started early and ended early. We'll just have to wait and see. One of the thing about the flu is you can never predict what's going to happen from one year to the next.

MONTAGNE: Rob, thanks very much.

STEIN: Thank you.

MONTAGNE: Rob Stein is NPR's health correspondent.

STEVE INSKEEP, HOST:

Now, if you are sick with the flu, there's only so much you can do. You can get rest, drink plenty of liquids, and maybe spend some time trying to figure out who passed on the illness. And there's an app to help you with that last part.

MONTAGNE: The Facebook application is called "Help, I Have the Flu." It will search the profiles of your friends to see if they've written the words coughing or fever - those keywords.

INSKEEP: This app is, of course, sponsored by a pharmaceutical company, which sells expectorants and decongestants.

MONTAGNE: But if you're not that interested in the flu blame game, you can find more scientific information. The Centers for Disease Control sponsors Flu View, which lets you use an iPhone to track influenza activity levels throughout the country. Transcript provided by NPR, Copyright NPR.