Why Can't I Get a Flu Shot While I'm Sick?

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There are very few people who can't or shouldn't get flu vaccines. Listed among the few other flu shot restrictions is the recommendation that you should not get a flu shot when you are significantly ill or have a fever. If you have just a minor illness, you can still get a flu vaccine, but anything more serious and you should hold off until you are better.

But why this recommendation? What will happen if you get a flu shot when you are sick?

There are actually two possibilities. It could take you longer to recover from your illness or your body may not respond as well as it should to the flu vaccine.

Longer Recovery Time

When you get a flu vaccine (or any other type of vaccine) it triggers an immune response in your body. Your immune system develops antibodies against the influenza virus that is in the vaccine so that it will recognize it and be able to fight it off if you are exposed to it again in the real world environment.

However, if you are sick when you are vaccinated, your immune system is already hard at work trying to fight the germs that have caused that illness. This means it will be harder for your body to develop antibodies to the flu virus at the same time. It could mean that it will take longer for you to recover from your illness as your immune system tries to do double duty.

Reduced Response to the Flu Vaccine

For the same reasons as stated above, if you get the flu vaccine when you are sick, your body may not develop adequate antibodies to the strains of influenza in the vaccines as it would otherwise.

If your body is busy fighting off a different infection, it may not develop strong enough antibodies to the strains of influenza in the vaccine, which could result in an increased chance that you could still get the flu. Neither of these things is guaranteed to happen if you get the flu vaccine when you are sick, but they are possibilities.

If you have just a mild illness, there is no reason to wait to get vaccinated. However, if you want to get the nasal spray flu vaccine and you are very congested, you may need to wait until your nose clears up so you have a better chance at getting the full benefit from that vaccine.

If You Have a Cold

Have you ever planned to get a flu shot and then woken up with a cold? Or maybe you are at your doctor's office and they offer you a flu vaccine but you aren't sure if you are really healthy enough to get it. Will it still work? Could it make you even sicker?

Having a cold isn't necessarily a reason to avoid getting your flu shot, but the symptoms you have may mean you need to put it off for a few days. For the most part, common cold symptoms do not prevent you from getting a flu vaccine. A cough, congestion, headache, and sore throat won't affect your body's response to the vaccine. 

The exception would be if you are running a significant fever (over about 101F). Since fevers are pretty uncommon with colds, it's unlikely this will be an issue. They are more common in children who have colds though, so if you are trying to get your child vaccinated, you should monitor her temperature if you think she is getting sick.

If your child has a fever, the pediatrician may decide that it is better to wait until the fever has resolved before giving any vaccinations (influenza or others).

If You Have a Fever

Depending on your temperature and your other symptoms, you may still be able to get your flu vaccine. If you have a fever over 101F or you are very ill, the CDC recommends waiting until your fever has returned to normal and you feel better before being vaccinated.

The reason for delaying the shot is pretty simple. If you are already sick, your body's immune system is working hard to fight off the germs that are making you sick.

When you get a vaccine, the immune system develops antibodies against the illness that the vaccine is designed to protect you from (in this case, the flu).

But if you are already sick and your immune system is trying to fight off another illness, it may not be able to develop the antibodies to the vaccine-preventable illness as easily. This means it is possible that it could take you longer to recover from your illness or the vaccine may not be as effective as it would have been otherwise.

When to Get the Flu Shot

If you have a temperature of 99 or 100F and no serious symptoms, there is no reason to hold off on getting your flu shot. These temperatures are not truly considered a fever and if you are not dealing with a moderate to severe illness, you should have no problem with the vaccine.

Your health care provider, nurse, or pharmacist that is administering the flu vaccine should ask you if you have a fever or are sick before giving it. However, if they do not, be sure to speak up or cancel your appointment if you are sick when it's time to get your vaccine.

Other Reasons Not to Get a Flu Vaccine

Other than being sick and running a fever, there are a few other reasons you should not get a flu vaccine. These include:

  • History of a severe allergic reaction to a previous flu vaccine.
  • Babies under 6 months old
  • History of Guillain-Barre syndrome after receiving a previous flu vaccine. If you have had Guillain-Barre syndrome, talk to your health care provider to determine whether or not you should get the flu shot.

Although the vaccine is recommended for everyone over 6 months old, there are certain groups of people that are considered to be at high risk for flu complications and should be vaccinated if at all possible. If you live with or care for someone in a high-risk group, it is equally important for you to be vaccinated to reduce the risk of spreading the flu.

A Word From Verywell

If you aren't sure whether your illness is significant enough to avoid getting the flu vaccine, talk to your health care provider. Another good rule of thumb—if you are so sick that you feel like you need to go to the doctor, you should probably wait to get your flu vaccine; if you are sick but still feel well enough to go about your daily routine and/or go to work, getting the vaccine should be fine.

Sources:​

CDC. Influenza (Flu) Vaccine Safety

CDC. Key Facts about Influenza (Flu)

CDC. Seasonal Flu Shot

CDC. Vaccine Effectiveness - How Well Does the Flu Vaccine Work?

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