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Side effects after a vaccine (including the COVID-19 shot)

Also called: Vaccine side effects, vaccine reaction, shot reaction, COVID vaccine side effects

Most vaccines cause short-lived side effects like a sore arm, tiredness, or mild fever that go away in 1 to 3 days. Serious reactions are rare.

CommonSore arm, tiredness, headache, mild fever
Usually lasts1 to 3 days
Rare but seriousSevere allergic reaction
ReportVAERS (vaers.hhs.gov)

Overview

Side effects show the immune system is building protection.

Severe allergic reactions usually happen within minutes to an hour, which is why you're watched briefly after a shot. After COVID-19 vaccines, heart inflammation (myocarditis) is rare, mostly in young males within a week.

Symptoms

Common signs:

  • Sore, red, or swollen arm
  • Tiredness
  • Headache
  • Body aches
  • Fever or chills

Less common

  • Swollen glands in the armpit
  • Nausea

Look up a symptom: Fatigue · Fever · Headache

When to get medical care

Call 911Trouble breathing, face or throat swelling, hives all over, a fast heartbeat, dizziness, or fainting.
Get care todayChest pain, a racing or pounding heartbeat, or shortness of breath in the week after a COVID-19 shot.
See a doctor soonRedness or soreness that gets worse after 24 hours, or side effects that last more than a few days.

Causes

The immune system's normal response to the vaccine. Rarely, an allergy to an ingredient.

Does it spread or run in families?

  • It isn't contagious. You can't catch it from someone else.

Who is more likely to get it

  • Past severe reaction to a vaccine

Possible complications

Diagnosis

Most side effects don't need a visit.

Questions you may be asked

  • Which vaccine and when
  • Past vaccine reactions

The exam

A check of the arm and vital signs.

Treatment

Side effects usually go away on their own.

Self-care

  • Use a cool, wet cloth on the arm
  • Keep moving the arm
  • Rest and drink fluids

Medicines

Medicines that may help:

MedicineHelps withGood to know
Pain and fever relievers
Aches and feverFollow the label.

OwieClear doesn't give doses: follow the label or your healthcare professional. Medicine names here are examples, not a full list.

Prevention

To feel better after shots:

  • Rest and drink fluids

Which doctor treats this

  • Start with your primary care provider (family doctor or internist).

Back to school, work, or sports

  • Most people keep up normal school and work. Rest when you need to.

Pregnancy and breastfeeding

  • If you're pregnant or planning to be, tell your prenatal provider about this condition.
  • Don't start or stop any medicine on your own. Some are safe in pregnancy and some need to be changed.
  • Ask before taking any pain reliever. The FDA advises avoiding ibuprofen and naproxen after 20 weeks unless your doctor says to.
  • Breastfeeding: Most medicines are fine, but ask. The NIH LactMed database lists what's known about each one.

Outlook

Side effects pass quickly for almost everyone.

Myths and facts

Myth: Side effects mean the vaccine made you sick.

Fact: A sore arm, tiredness, or mild fever usually means the body is building protection.

Getting ready for your visit

Bring a list of your symptoms and medicines.

What to bring

  • Your vaccine record

Questions to ask

  • Should I get future doses?
  • How do I report a reaction?

Research studies

Research studies test new ways to find and treat health problems. Some are looking for volunteers. Talk with your doctor before joining one.

Search ClinicalTrials.gov for studies on Side effects after a vaccine (including the COVID-19 shot)

Sources

Last updated 2026-11-12.