FAQ – Side Effects and What to Do
What side effects are normal after vaccination?
Common side effects include a sore arm, redness or swelling at the injection site, tiredness, headache, muscle aches, chills, or a low fever. These usually start within 1 to 2 days and go away within a couple of days.
What can I do to feel better after a vaccine?
- Use your arm: gentle movement can reduce soreness.
- Cool compress: helps with pain and swelling at the injection site.
- Rest and fluids: especially if you feel tired or achy.
- Pain or fever medicine: you can use over-the-counter medicine if you normally can take it. If you have questions about what is safe for you or your child, ask your health care provider.
Is it better to take medicine before the vaccine to prevent side effects?
Usually no. It is generally fine to take medicine after vaccination if you need it for symptoms. If you have questions about your situation, ask your provider.
What is swelling or redness at the injection site, and when should I worry?
Mild redness, warmth, and swelling are common and should improve within a few days. Contact a health care provider if the redness keeps spreading, the pain is getting worse after 24 hours, you see pus, or you have a high fever.
Can vaccines cause fever?
Yes, a low fever can happen. Fever is a normal sign your immune system is responding. For children, contact a provider if fever is high, lasts more than 48 hours, or if you are worried about how your child looks or acts.
What if my child cries a lot or seems very fussy after vaccines?
Some fussiness and changes in sleep or appetite can happen for a day or two. Comfort measures like cuddling, feeding, and rest can help. Call your provider if your child is difficult to wake, has persistent inconsolable crying, shows signs of dehydration, or you are concerned.
What if I feel dizzy or faint after a vaccine?
Fainting can happen, especially in teens and young adults. If you feel lightheaded, sit or lie down right away and tell staff if you are at a clinic. If symptoms do not improve within a few minutes, seek medical help.
What are signs of a severe allergic reaction?
Severe allergic reactions are rare, but they can be serious. Call 911 right away if you have:
- Trouble breathing or wheezing
- Swelling of the face, lips, tongue, or throat
- Hives all over the body
- Severe dizziness or feeling like you might pass out
- Fast heartbeat or confusion
When should I contact a health care provider after vaccination?
Contact a provider if:
- Side effects are getting worse after 24 to 48 hours
- Fever is high or lasts more than 48 hours
- You have symptoms that concern you or interfere with daily activities
- A child is unusually sleepy, hard to wake, or not drinking fluids well
What should I do if I think I had a reaction to a vaccine?
Seek urgent care for severe symptoms. For non-emergency reactions, contact your health care provider. You can also report side effects to vaccine safety monitoring systems (for example, VAERS), and your provider or clinic can help.
Are serious side effects possible?
Yes, but they are rare. Health agencies monitor vaccine safety closely. The risk of serious illness from vaccine-preventable diseases is usually much higher than the risk of a serious vaccine reaction. If you have a history of severe allergies or a past vaccine reaction, talk with your provider before vaccination.
Do different vaccines have different side effects?
Yes. Some vaccines are more likely to cause a sore arm, and some are more likely to cause fatigue or fever. Your provider or the Vaccine Information Statement (VIS) for that vaccine will list what is most common and what to watch for.
Where can I find official side effect information for a specific vaccine?
Look for the Vaccine Information Statement (VIS) or the vaccine’s product information. Clinics can provide this at the time of vaccination, and it is often available online through public health sources.
If I had side effects after a dose, should I still get the next dose?
Often, yes. Mild to moderate side effects are common and do not mean you should stop the series. If you had a severe allergic reaction, or you are unsure, talk with your health care provider before getting another dose.