COVID-19 booster vaccines have been widely administered to enhance protection against severe illness and hospitalization caused by evolving variants of the virus1 . While booster doses are generally safe, they can cause side effects similar to the initial vaccine series, which are mostly mild and short-lived2 . Understanding the types of boosters available, their common and rare side effects, and when to seek medical advice can help individuals make informed decisions and manage their health effectively after vaccination3 .
Types of COVID-19 Booster Vaccines
The U.S. Food and Drug Administration (FDA) has authorized three main COVID-19 booster vaccines: Pfizer-BioNTech, Moderna, and Novavax3 45. Pfizer-BioNTech and Moderna boosters are bivalent mRNA vaccines targeting both the original SARS-CoV-2 strain and the Omicron variant, while Novavax offers a monovalent protein subunit booster based on the original strain3 45.
| Vaccine | Type | Target Strains | Authorized Age Group | Notes |
|---|---|---|---|---|
| Pfizer-BioNTech | Bivalent mRNA | Original + Omicron variants | 6 months and older | Authorized broadly for all eligible ages3 5 |
| Moderna | Bivalent mRNA | Original + Omicron variants | 6 months and older | Excludes individuals with severe allergic reactions3 5 |
| Novavax | Monovalent protein subunit | Original strain only | 12 years and older | For those who cannot or will not receive mRNA vaccines3 45 |
Who Is Eligible for COVID Booster Shots?
Eligibility for COVID-19 boosters varies by vaccine type and individual health status. Both Pfizer-BioNTech and Moderna bivalent boosters are authorized for individuals aged 6 months and older, with Moderna excluding those who have contraindications such as severe allergic reactions3 45. Novavax's monovalent booster is available for people aged 12 and older who have not received a previous booster and cannot or will not receive an mRNA vaccine3 45.
The Centers for Disease Control and Prevention (CDC) recommends that people receive age-appropriate vaccine products and dosages based on their age at vaccination6 . Those with moderate or severe acute illnesses should postpone vaccination until recovery3 45. Individuals with a history of myocarditis or pericarditis within three weeks of a previous dose or multisystem inflammatory syndrome (MIS) in the past three months should delay booster vaccination3 45.
Common Booster Side Effects
Booster shot side effects are generally similar to those experienced after the primary vaccine series and are mostly mild, resolving within a few days2 78. Common symptoms include pain at the injection site, fatigue, headache, muscle or joint pain, and fever2 78.
Side Effects of Moderna Booster
Moderna booster recipients frequently report injection-site redness and swelling7 8. Muscle or joint pain is also common following Moderna booster vaccination7 8. Other side effects such as fatigue, fever, and chills may occur but typically resolve quickly7 8.
Side Effects of Pfizer-BioNTech Booster
The Pfizer-BioNTech booster has side effects comparable to those of the Moderna booster2 78. Common symptoms include injection-site pain, fatigue, headache, muscle or joint pain, fever, and bone pain, similar to those experienced after the second dose of the primary series2 78.
Side Effects of Novavax Booster
Novavax booster recipients report fewer side effects compared to mRNA vaccine recipients3 45. Common side effects such as injection site pain, swelling, headache, fatigue, muscle ache, and fever are less frequent and generally milder3 45.
Rare Booster Side Effects
Rare but serious side effects following COVID-19 booster vaccination include myocarditis, anaphylaxis, blood clots, and neurological symptoms, though these events are extremely uncommon and often not definitively linked to vaccination3 45.
Myocarditis, an inflammation of the heart muscle, is the most recognized rare side effect of mRNA COVID-19 vaccines, occurring predominantly in adolescent and young adult males within seven days of vaccination3 45. Among over 192 million mRNA vaccine recipients in the U.S., 1,626 cases of myocarditis were reported within seven days of vaccination3 45. Most cases are mild and resolve with treatment and rest6 .
Other rare adverse events reported include constipation, dizziness, concentration difficulties, vertigo, sore throat, hearing changes, tinnitus, and anaphylaxis3 45. Anaphylaxis is a severe allergic reaction that requires immediate treatment but occurs at a rate of approximately 5 cases per one million vaccine doses administered6 . Blood clotting disorders such as thrombosis with thrombocytopenia syndrome (TTS) have been linked to certain vaccines but are very rare and primarily associated with vaccines no longer widely used in the U.S. 6.
Booster Shot Precautions and Safety
Certain precautions are recommended before receiving a COVID-19 booster vaccine to ensure safety3 45. Vaccination should be postponed in individuals with moderate or severe acute illnesses until they recover3 45. Those who have experienced myocarditis or pericarditis within three weeks of a previous COVID-19 vaccine dose should not receive another dose3 45. Individuals who have had multisystem inflammatory syndrome (MIS) in the past three months should delay booster vaccination3 45.
“Myocarditis has been most frequently seen in adolescent and young adult males within 7 days of their second mRNA COVID-19 vaccine dose. Most patients with myocarditis after COVID-19 vaccination respond well to medicine and rest and feel better quickly.”
— Centers for Disease Control and Prevention6
For individuals with a history of non-severe allergic reactions to vaccine ingredients, alternative vaccine options may be considered3 45. Consultation with a healthcare provider is advised to discuss potential risks and determine the best vaccination plan3 45.
When to Contact Your Doctor
Most side effects from booster shots are mild and resolve within a few days2 78. However, you should contact a healthcare provider if side effects persist beyond a few days or if you have concerns about your symptoms2 78.
Immediate medical attention is necessary for severe symptoms such as chest discomfort or tightness, swelling of the face and throat, difficulty breathing, or signs of a severe allergic reaction2 78. These symptoms may indicate myocarditis, anaphylaxis, or other serious conditions requiring urgent care6 .
💡 Did You Know? The CDC recommends monitoring all vaccine recipients for at least 15 minutes after vaccination to quickly address any immediate allergic reactions6 .
Managing Booster Side Effects
Simple measures can help reduce discomfort and side effects after a booster shot2 78. Dressing comfortably can help manage fever, while keeping the arm moving can reduce soreness and stiffness2 78. Applying a clean, cool cloth to the injection site can alleviate swelling and pain2 78.
Rest and hydration are also important to support recovery from side effects2 78. Over-the-counter pain relievers such as ibuprofen or acetaminophen may be used after vaccination to ease symptoms, but taking these medicines before vaccination to prevent side effects is not recommended as it may affect vaccine effectiveness6 .
💡 Did You Know? COVID-19 vaccines are safe during pregnancy and breastfeeding, with no identified safety concerns for mothers or babies9 .
Summary of Booster Side Effects
Booster shots may cause side effects similar to those of the primary vaccine series, including headaches, muscle pain, and injection site swelling2 78. Most side effects are mild and resolve within a few days without intervention2 78. Novavax booster recipients generally report fewer and milder side effects compared to mRNA vaccine recipients3 45.
Rare side effects such as myocarditis, anaphylaxis, and blood clotting disorders are extremely uncommon but require prompt medical attention if symptoms arise3 45. Monitoring systems like the Vaccine Adverse Event Reporting System (VAERS) and active surveillance by health agencies continue to ensure the safety of COVID-19 booster vaccines6 .
Taking simple steps such as dressing comfortably, moving the arm, and applying cool compresses can help manage common side effects2 78. If side effects persist or severe symptoms develop, contacting a healthcare provider is essential for timely care2 78.
