Flu comprises of more than one virus.

We call it the flu like there’s only one, but every year the flu is different, and is not singular — there are different types of flu viruses. The reason we call it the flu instead of being more specific is because each of the viruses function more or less the same, and because they pop up like clockwork every year in a seasonal epidemic. With so many viruses circulating, it’s a yearly challenge for scientists to predict which three or four will prove to be the season’s most prevalent and potent flu viruses.

Predicting what the predominant strains of the flu will be each winter is done through a lot of surveillance around the world. Scientists study all the cases of flu that happen around the world to try to predict each season in advance.

Once they pinpoint the strains that appear to be the epidemic ones, scientists grow the vaccines either in chicken eggs, or in specialized bacteria.


The fact that the viruses in the vaccine are dead is a critical point: a dead virus cannot infect you. It just can’t. A lot of times people will say they or their children got the flu from the vaccine, and that is just not possible. That said, some people do feel bad after: muscle aches, low grade fever, achy arm [where they had the injection]. It is usually a good sign and shows that it means your immune system is having a response, which is what we want. What you don’t want is an allergic reaction, of course — but these are exceedingly rare.

Note that even if you’re among the lucky few who feel totally fine after the flu shot with no soreness or low fever, this does not mean your immune system didn’t respond or that the flu vaccine didn’t work.


Now, let’s say you get the flu shot and two days later you get the flu. Well, you didn’t get sick because of the vaccine (because again, dead viruses are non-infectious), but it does point to a loophole: the vaccine takes two to three weeks to have full effect. This is why doctors recommend getting it as soon as it’s available. If you get the vaccine now, you should be covered through the duration of the flu season, which can start as early as mid-fall, and end as late as early spring. How long the vaccine lives in your system depends on your immune system, but for the general patient it’s between six months and a year.

The vaccine is not that long-lived in part because the viruses that cause the flu are very smart and keep changing to infect us. This is why you should get the flu shot every year.


Optimally, the flu vaccine will prevent you from getting the flu, but that’s actually secondary to the primary goals of the vaccine which are to prevent epidemic and to reduce the cases of severe flu infection.

How long the vaccine lives in your system depends on your immune system, but for the general patient it’s between six months and a year.

At its most effective the flu shot would prevent you from getting the flu, but really when you look at studies, the purpose of the vaccine is to reduce the number of severe flu illnesses that require going to the hospital. The real goal is even if you do get the flu that you are not as sick as you would be if you had not gotten the vaccine.

Basically, if your immune system is primed to deal with the virus, should it still attack you, you likely won’t develop a severe flu infection. Another purpose of the flu vaccine: not everyone can get it, so it’s important that people who can receive it do so that “we build herd immunity”

Some people who have immunological diseases, or an organ transplant, have cancer or other conditions may not be strong enough to get a flu vaccine but if those around them are vaccinated, we develop a herd immunity, so that hopefully the few people who can’t get the vaccine will not get infected.

The vast majority of people over the age of six months are a to get a flu shot.


A flu shot helps protect newborns from getting the flu. Babies can’t get the flu vaccine until thy are six months, so by getting the vaccine herself, the mom will make the antibodies and pass it onto the baby, protecting them from severe flu for the first months of their lives.

Still, it is totally understandable to be concerned, so if you are pregnant and have questions, talk to your doctor first. And if you’re a parent who is unsure if your six month old is really ready for the flu vaccine, pay a visit to your pediatrician.

Children, like elderly people, are indeed more susceptible to developing severe flu. This is in part because they’re ultra exposed in schools and daycare facilities (and you know, they may not have the best hand hygiene), but also because their immune systems haven’t been toughened up.

Very important: Always make sure you discuss and make decisions about your eye care based upon a formal appointment with your optician.

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