Is the flu shot at all effective after one week?

December 25, 2012 10:39 AM

I'm travelling up and down the northeast US starting next Sunday. The first person I'm going to see has told me she's coming down with the flu. If I get a flu shot now (or I guess tomorrow since it's Christmas) will it do me any good?
posted by Busoni to health & fitness (17 answers total)

I would say probably, but this year's flu is completely awful. DH and I have both had it, and it put us out of commission for more than a week each. My grandmother and sister-in-law both had this flu turn into pneumonia. If you can at ALL avoid staying with the first person, please do so.
posted by roomthreeseventeen at 11:02 AM on December 25, 2012 [1 favorite]

Did this person have a flu shot herself this year? I'm going to echo roomthreeseventeen that the flu this season is absolutely dreadful. Moreover, I came down with it about three weeks after getting the immunization myself. The flu shot gives you a better fighting chance of not catching the flu going about your day to day life, but I definitely wouldn't consider it solid protection when you're knowingly exposing yourself to someone who already has the flu. Rearrange your trip.
posted by telegraph at 11:06 AM on December 25, 2012

By the time you see her, she will have been symptomatic for at least a few days. Will she still be contagious?
posted by zippy at 11:14 AM on December 25, 2012

A lot of people mean "sniffly head cold" when they say "flu". If she says "I think I am probably going to die from this" then yeah, I would avoid staying there if possible. If it's just a common cold, meh. (Get a flu shot either way, though. r317 is correct, this season's flu is fucking medieval.)
posted by elizardbits at 11:19 AM on December 25, 2012 [2 favorites]

Most of the time when someone tells you they have the flu, they actually have a cold. There is no one symptom that proves they have the flu. Colds can cause vomiting, fever, and all the symptoms we normally associate with the flu. Colds can be miserable too, so it's a good idea to protect yourself either way.

The flu vaccine takes about 2 weeks to reach full effect. The vaccine contains 3 strains of flu based on last years flus, and has a wide range of efficacy depending on how good a job the people who make the vaccine did in guessing which strain would be the issue in the current year.

In general, colds and flus are most infectious before symptoms start, and then become less and less infectious over about 5 to at most 10 days, when they are not infectious anymore.

Frequent hand washing, adequate rest, and avoiding being sneezed on or near might help.

Good luck!
posted by latkes at 11:19 AM on December 25, 2012

I guess my main question (although other advice/tips/info is welcome) is whether I'm doing any good by getting a shot one week before maybe being exposed to the virus. (It's most likely the flu, her parents apparently came down with it last week and it's apparently pretty miserable.) The information I could find said it takes two weeks for the vaccine to become effective, so I'm wondering if it's completely useless until those two weeks. Although of course it would help down the line, after two weeks, since obviously this one person isn't the only flu vector in America.
posted by Busoni at 11:49 AM on December 25, 2012

Yes, two weeks is correct. But it can't hurt to get it anyway (except for the tiny needle). As you point out, it might protect you from other flu sources.
posted by grouse at 11:55 AM on December 25, 2012

My wife and son both got the Flu (not a cold) this year. I had a Flu shot 3 days before symptoms showed up and felt a little off, but didn't get the full impact.
posted by Jacob G at 12:39 PM on December 25, 2012

Everyone is different and no one can predict the exact time it will take for you to have an appropriate immune response. You're likely to have some response in a week, but there's a high chance that this is not actually the flu, but rather a bad cold, and a smaller chance that it is the flu, but it's a flu strain that isn't covered by the vaccine, so either way, you're taking your chances. But might as well get the shot because it lowers the likelihood of you getting sick.
posted by latkes at 1:16 PM on December 25, 2012

If I were the person with the flu, I wouldn't want any visitors (either the staying-with-me kind or the meet-for-dinner kind). Yfriend'sMMV.
posted by rtha at 1:21 PM on December 25, 2012 [2 favorites]

In general, colds and flus are most infectious before symptoms start

This is absolutely and completely wrong and was in a "best answer" so I thought I better point that out. It is a widespread belief but that doesn't make it any less wrong.

Hell, it doesn't even make any sense. How do you think viruses are spread? In droplets. How are the droplets spread? By sneezing, coughing, and other ways of spreading droplets. So how could you possibly be most contagious before you start spreading the virus?

Anyway, no, she wasn't most infectious before symptoms started. She is most infectious when she is coughing and sneezing. It's possible to develop a lingering dry cough after the virus is gone but that's a different issue.
posted by Justinian at 2:23 PM on December 25, 2012 [2 favorites]

A good rule of thumb: If you're asking yourself "do I have a cold or is it the flu?", you have a cold. If you're lying on the floor hoping not to die, it is the flu.
posted by Justinian at 2:24 PM on December 25, 2012 [4 favorites]

For the first week after exposure to an immunogen you are in what they call the lag phase, after which your immune response picks up dramatically. So you won't have the kind of immune response up you'd have if you got immunized a month ago, but, assuming your friend has something covered in the current flu vaccine, your immune system will be going into things pre-informed rather than completely flat footed.
posted by Kid Charlemagne at 5:31 PM on December 25, 2012 [4 favorites]

For the truly nerdy, I just re-read the information on uptodate about cold and flu transmission windows.

From a flu article:

Duration of shedding — In otherwise healthy adults with influenza infection, viral shedding can be detected 24 to 48 hours before illness onset, but is generally at much lower titers than during the symptomatic period [11]. In a review of 56 studies of 1280 healthy adults who were experimentally challenged with influenza virus, shedding of influenza virus increased sharply one-half to one day following exposure, peaked on the second day, and then rapidly declined [12]. The average duration of shedding was 4.8 days (95% CI 4.3 to 5.3 days). Shedding ceased after six or seven days in most studies but occurred for up to 10 days in some. Studies of natural infection in healthy adults have shown similar results [2,11,13-15].

And the rhinovirus article (rhinovirus is a common cause of colds, though there are others):
Rhinovirus is present in nasal secretions for five to seven days, but may persist as long as two to three weeks in the nasopharynx [10]...

... In [a] study using married couples, the conditions required for transmission were present only on the second or third day after inoculation, as this is the time of greatest viral shedding [12]. Thus, the period of maximum contagiousness is most likely within the first five days of illness. Oral inoculation is an ineffective route of transmission [6].

I amend my comment to agree with Justinian that when you are sneezing and coughing all over everyone you are more likely to infect them than when you are not. But to be clear, people with both cold and flu viruses shed more virus at the beginning of the infection, and that rapidly decreases each day that they are sick.
posted by latkes at 7:41 PM on December 25, 2012 [1 favorite]

Ok, I would just say there is a difference between how contagious someone is and the amount of virus they are shedding. A review of the literature will reveal (as in this journal article) that "there is scant, if any, evidence that asymptomatic or presymptomatic individuals play an important role in influenza transmission".

Anyway, good luck OP. If I were you I would completely avoid contact with someone who has the flu unless absolutely necessary.
posted by Justinian at 9:46 PM on December 25, 2012

The last time I had the flu (h1n1) I was so sick that my husband had to take a week off work to take care of me, and in one case rush me to the doctor when I went into respiratory distress. (I was short of breath and winded, like I'd just climbed a flight of stairs, but I'd been sitting on the couch for hours. Once I realized I couldn't catch my breath to the point where I couldn't really talk, we high-tailed it to medical attention.) There is no way I would have wanted company, or to give it to anyone else. I was sick for three weeks with that one.
posted by KathrynT at 12:25 AM on December 26, 2012

Just get the shot now, because you don't want the flu regardless of where you catch it.

Do not visit, because they will most likely be contagious for as long as they have symptoms, and they also won't be capable of hosting you. I don't know if I've had the flu or not (it could have been bacterial and I did resort to antibiotics which seemed to work) but if this is the flu, you don't want it, believe me. Keep your vaccinations up to date and your hands washed with soap, and don't visit the plague house.
posted by tel3path at 1:26 PM on December 26, 2012