Understanding Bivalent COVID-19 Booster Vaccines: Side Effects, Safety, and Guidance

Explore what to expect after your next immunization and how experts keep you protected.

By Medha deb

Created on Sep 22, 2025

Explore what to expect after your next immunization and how experts keep you protected.

The advent of bivalent COVID-19 booster vaccines marked an important evolution in the public health response to SARS-CoV-2, especially following the emergence of new variants. These boosters were designed to target both the original strain of the virus and newer, more transmissible variants such as Omicron. As more individuals consider receiving the bivalent booster, questions about side effects, safety, and eligibility have become increasingly common. This article provides a thorough overview of what to expect before, during, and after bivalent booster vaccination, drawing on current evidence and expert guidance up to 2025.

What Is a Bivalent COVID-19 Booster and Why Was It Developed?

The bivalent COVID-19 booster differs from the original monovalent vaccines by including mRNA components from both the ancestral SARS-CoV-2 strain and one or more Omicron lineages (such as BA.4, BA.5). This dual-action approach was developed to enhance protection against both early forms of the virus and the more recent Omicron subvariants that account for the majority of cases worldwide.

Bivalent boosters are authorized for use in individuals who have completed a primary vaccination series or received previous booster doses.
The goal: Broaden immunity and improve effectiveness against emerging variants.

Common Side Effects of Bivalent COVID-19 Booster Vaccines

Side effects following bivalent boosters are generally consistent with those observed after previous mRNA COVID-19 vaccines. Most recipients experience only mild, temporary symptoms that resolve within a few days.

Most Common Side Effects

Pain at the injection site (soreness, redness, or swelling)
Fatigue
Headache
Muscle aches (myalgia) or joint pain
Chills
Fever
Nausea or vomiting (more common with Moderna than Pfizer)
Swollen lymph nodes

Large-scale safety surveillance found that between 45% and 70% of adults reported some local reaction (like arm pain) after receiving the bivalent booster, while 30% to 53% reported fatigue and 19% to 43% experienced headache. Other symptoms were less frequent and typically short-lived.

Severity and Duration

The vast majority of side effects were classified as mild to moderate and resolved within 1–2 days.
Severe reactions are very rare; most people can continue with normal activities or only miss one day of work or routine duties.
Less than 0.5% of recipients required medical attention for post-vaccination issues.

Side Effect Comparison: Bivalent vs. Previous Boosters

Side Effect	Bivalent Booster	Monovalent/Original Booster
Injection site pain	45–70%	50–75%
Fatigue	30–53%	35–60%
Headache	20–43%	25–40%
Fever	10–26%	10–28%
Missed regular activities	8–13%	10–15%

According to active surveillance data, the bivalent boosters produced side effects of similar frequency and severity as prior mRNA vaccines, with no substantial increase in serious adverse reactions.

Uncommon and Serious Side Effects: Myocarditis, Pericarditis, and Allergic Reactions

While most bivalent booster side effects are mild, rare adverse events can occur. Safety monitoring systems such as the CDC’s Vaccine Adverse Event Reporting System (VAERS) collect and analyze these events:

Myocarditis (inflammation of the heart muscle): Extremely rare, with a small number of cases reported primarily in young males after mRNA vaccination. The risk after bivalent boosters appears to be similar to or lower than after previous monovalent doses.
Pericarditis (inflammation of the lining around the heart): Also very rare; increased risk was observed mainly in the first week after vaccination among males aged 12–50 and females 30–50 years, but overall numbers remain low.
Severe allergic reactions (anaphylaxis): Extremely rare, occurring only in a small fraction of vaccinated individuals, typically within minutes to hours of receiving the shot. Symptoms may include rash, throat swelling, breathing difficulties, or a rapid heartbeat. Onsite monitoring for 15–30 minutes after vaccination is recommended to promptly treat any reaction.

Of more than 22 million bivalent booster doses administered as of 2025, only a handful of myocarditis and pericarditis cases have been reported, and most patients recovered fully with appropriate care.

Differences Between Moderna and Pfizer Bivalent Boosters

Both Moderna and Pfizer bivalent boosters are mRNA-based vaccines, with small differences in their formulation and the specific Omicron variants targeted.
Data show similar rates of side effects between the two, with a slightly higher proportion of mild reactions (such as arm pain or fatigue) reported after the Moderna booster in some studies.
Rates of missing regular activities or needing medical care after vaccination are low for both brands: less than 0.5% for medical attention, roughly 8% (Pfizer) to 13% (Moderna) for missed activities.

Who Should Receive the Bivalent Booster?

The Centers for Disease Control and Prevention (CDC) and other health authorities recommend the bivalent booster for:

Individuals who completed a primary COVID-19 vaccine series (including those who have received prior boosters or who were previously infected)
Adults and adolescents eligible under current local guidelines (age cutoffs may evolve as more data become available)
People at higher risk of severe illness from COVID-19, such as older adults, those with underlying medical conditions, and immunocompromised individuals

Consult your healthcare provider for recommendations tailored to your age, health status, and time since last COVID-19 vaccine or infection.

Safety and Efficacy Monitoring

Ongoing monitoring by agencies like the CDC, FDA, and international counterparts confirms that bivalent COVID-19 booster vaccines have an excellent safety profile. The vast majority of post-vaccination symptoms are mild, resolve quickly, and do not require medical intervention. Serious adverse events are very rare.

Active safety surveillance includes automated follow-up surveys and adverse event reporting systems.
Most incidents of fever, fatigue, or headache are mild and do not result in missed school, work, or require hospitalization.
Hospitalizations for serious side effects remain extremely rare in all age groups.

Can You Get a Flu Shot or Other Vaccines at the Same Time?

The CDC states that it is safe and effective to get a COVID-19 booster and a flu shot at the same appointment. There are only a few exceptions:

If you have recently received the monkeypox vaccine ACAM2000, you should wait four weeks before getting a COVID-19 vaccine due to a small risk of myocarditis.
No waiting period is needed with the JYNNEOS monkeypox vaccine, unless you develop symptoms of myocarditis or pericarditis.
If you receive other routine vaccines, discuss timing with your healthcare provider, especially if you’ve had prior allergic reactions.

Combining these vaccines helps protect you against several potentially severe respiratory viruses as they often circulate at the same time.

How to Prepare for Your Bivalent Booster Appointment

Plan low-impact activities for the day of and the day after your booster, if possible.
Stay hydrated and eat a light meal before your appointment.
Bring your COVID-19 vaccination card or records to update your immunization history.
Notify the provider of any history of allergies, myocarditis, pericarditis, or previous vaccine reactions.
Plan to be observed for 15–30 minutes after your vaccine in case you have an allergic response.
Have acetaminophen or ibuprofen available at home in case of mild side effects (consult your healthcare provider before use).

Caring for Post-Vaccination Side Effects

Most side effects can be managed at home. Strategies include:

Rest and drink plenty of fluids
Apply a cool compress to the injection site for relief
Use acetaminophen or ibuprofen for pain or fever, if medically appropriate

Contact a healthcare provider if you experience:

Shortness of breath, chest pain, persistent palpitations, or other symptoms suggestive of myocarditis/pericarditis
Severe allergic reaction symptoms: swelling of the face/throat, difficulty breathing, widespread rash
High fever that lasts more than 48 hours or new symptoms of concern

FAQs: Bivalent COVID-19 Booster Vaccine Side Effects and Safety

Q: Are the side effects after a bivalent booster worse than earlier COVID-19 vaccines?

A: For most people, side effects are similar to, or milder than, those experienced after earlier doses. They usually resolve within a day or two and rarely interfere with daily activities.

Q: Should I worry about myocarditis or pericarditis?

A: These conditions are very rare after bivalent boosters. The small risk is mostly observed in adolescent males and young adult males, and the vast majority recover fully. For most people, the benefits of vaccination outweigh the risks.

Q: Is it safe to get a bivalent booster and flu shot together?

A: Yes. Health authorities recommend co-administration of COVID-19 and flu vaccines to ensure maximal protection against both viruses during peak seasons.

Q: Are any groups at higher risk for severe side effects?

A: Severe allergic reactions are most likely in people with a history of vaccine allergies. Myocarditis risk is slightly higher in young men, but remains very rare. Immunocompromised or chronically ill individuals should discuss benefits and risks with their healthcare providers.

Q: What should I do if I have a concerning reaction after vaccination?

A: Seek immediate medical care for symptoms such as chest pain, trouble breathing, facial/throat swelling, or a rapidly spreading rash. For mild symptoms such as fever or soreness, rest and over-the-counter medications are usually sufficient.

Key Takeaways

The bivalent COVID-19 booster provides broad protection against original and Omicron variants.
Most side effects are mild, limited to soreness or fatigue, and resolve quickly.
Serious side effects like myocarditis and anaphylaxis are extremely rare.
Health authorities continue to recommend the bivalent booster for eligible individuals to help prevent severe COVID-19 outcomes.
For personalized advice on vaccine timing and co-administration with other vaccines, consult your healthcare provider.

References and Further Reading

Centers for Disease Control and Prevention (CDC): Safety Monitoring of Bivalent COVID-19 mRNA Vaccine
World Health Organization: COVID-19 Vaccine Information
AusVaxSafety: Bivalent COVID-19 Vaccine Active Surveillance Data
American Medical Association: Answering Patients’ Questions about the Bivalent COVID-19 Vaccine

References

Author

medha deb

Medha Deb is an editor with a master's degree in Applied Linguistics from the University of Hyderabad. She believes that her qualification has helped her develop a deep understanding of language and its application in various contexts.

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