Sometimes the "ouch" of a vaccine doesn't end right after the shot is given. Soreness or a low fever may appear afterwards — one sign the vaccine is working! — along with fussiness.
But how likely is it that your baby will have vaccine side effects, especially serious ones? Here's what you need to know about the nature and likelihood of your baby having a reaction to a shot.
Are a fever and other side effects from vaccines possible?
Vaccines are safe, but like any medicine, they do sometimes come with the possibility of a few side effects. Most of the time, these reactions to vaccines are mild, localized — there's some soreness or redness where the shot is given — and brief, lasting no more than a day or two.[1]
"Vaccines are one of the safest and most effective ways to protect children from serious diseases," says Florenica Segura, M.D., a fellow of the American Academy of Pediatrics (AAP) who works at Einstein Pediatrics in Vienna, Virginia, and is a member of the What to Expect Medical Review Board. "Like any medication, vaccines can have side effects, but the vast majority are mild."
A low-grade fever may also occur, but anything more serious is very rare.[2]
"It’s completely normal for babies to have mild side effects like a fever, fussiness, or soreness after a vaccine — this just means their immune system is doing exactly what it should, building protection against serious diseases," Dr. Segura says.
Proving that a vaccine is related to a specific side effect isn't easy. Babies and toddlers tend to get sick frequently, so there's a chance your child could be coming down with something right around the time the vaccine is given.
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That's why some parents may believe that their baby's vaccine caused the illness, when in reality germs picked up at day care, the store, or a playdate are to blame.
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What should I do if my baby has a fever or other side effects from a vaccine?
A cold pack applied after the shot can help reduce soreness or swelling, as can moving the arm or leg in which the shot was given. If there's any redness or swelling at the injection site, you can also place a warm compress on the area to increase blood flow, which may help reduce discomfort and speed up healing.
You can also "bicycle" a baby's legs to help bring relief, or encourage a toddler to do a few rounds of head-and-shoulders-knees-and-toes.
A non-aspirin pain reliever such as acetaminophen (ages 3 months and older) or ibuprofen (ages 6 months and older)[3] can help with residual achiness and low-grade fever, so ask the doctor about that before you leave the office. Keeping your little one hydrated and dressed in light clothing can also help, Dr. Segura says.
Vaccines are very safe, but it’s possible for your little one to develop certain side effects after she gets her shot. Your child might feel soreness in the area where her shot was given, have a low fever that appears afterwards, or seem a little fussier than usual.
Most vaccine side effects are mild, though. Any more serious side effects from vaccines are extremely rare.
To soothe your little one after her shots, you can apply a cold pack to reduce swelling, or offer non-aspirin pain reliever such as acetaminophen (if she’s 3 months or older) or ibuprofen (if she’s 6 months or older) to manage her fever.
While severe side effects are rare, you should always let your child’s pediatrician know right away if you notice any serious symptoms. That includes a very high fever, sustained crying, seizures, an allergic reaction, changes in behavior, or anything else that seems concerning to you.
When to call the doctor about vaccine side effects
Though severe vaccine side effects are rare, you should call the pediatrician right away if your baby has any of the following reactions or symptoms within two days of getting a shot:[4]
- High fever (100.4 degrees Fahrenheit or higher for babies under 3 months old and 101.5 or higher for babies 3 months and older)
- Crying for more than three hours at a time (not to be confused with colic) or a high-pitched cry that lasts more than one hour
- Seizures or convulsions — which may be related to a very high fever
- Severe, persistent seizures or major alterations in consciousness
- Listlessness, unresponsiveness or excessive sleepiness
- An allergic reaction such as swelling of mouth, face, or throat; breathing difficulties; or a rash — which requires immediate medical attention and a call to 911
- Behavior changes — anything that's not normal for your child warrants a call to the pediatrician just to be on the safe side
Though these side effects could be unrelated to the vaccine and could be signs of another illness, call your doctor immediately if your child has any of these more serious symptoms (or others not on the list).
If your doctor believes your little one is having a reaction to a vaccine, they (or you) should report it to the Vaccine Adverse Event Reporting System (VAERS) at 1(800) 822-7967 or vaers.hhs.gov. Experts analyze VAERS data and look for patterns that could indicate any possible safety issues with vaccines.
"When we think about safety, it’s important to compare the risks: The diseases we vaccinate against, like measles, whooping cough, and meningitis, can cause severe illness, hospitalization, or even death," says Dr. Segura. "Choosing not to vaccinate isn’t a risk-free decision; it’s choosing a far greater risk. The bottom line is that vaccines save lives, and their benefits overwhelmingly outweigh any potential risks."
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