What Will Happen If I Get a Flu Shot While I'm Sick?

What will happen if you get a flu shot while you are sick?. Zave Smith/Image Source/Getty Images

Listed among the few other flu shot restrictions, is the recommendation that you do not get one when you are moderately to severely 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 already 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 influenza in the vaccine, which could result in an increased chance that you could still get the flu.

Neither of these things are 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. ( The nasal spray flu vaccine is not recommended for use during the 2016-2017 flu season due to concerns about it's efficacy. The CDC's Advisory Committee on Immunization Practices has recommended that it not be used at this time. There are still many other flu vaccine options available.)

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.

If you are concerned or have questions about getting sick after a flu shot or you think the vaccine may have made you sick, see:


Vaccination & Vaccine Safety. Prevention & Vaccination. Flu.gov. Department of Health and Human Services. 21 Nov 13.

Seasonal Flu Shot Questions & Answers. Seasonal Influenza (Flu) 26 Sep 13. US Centers for Disease Control and Prevention. Department of Health and Human Services. 21 Nov 13.

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