What to Know About Pneumovax 23 Side Effects

If you're about to get Pneumovax 23 — or you just received it and want to know what's normal — this guide covers exactly what to expect. Like all vaccines, Pneumovax 23 can cause side effects, but most are mild and go away on their own within a day or two. Serious reactions are rare.

Here's a breakdown of common and serious side effects, who may be more at risk, and when it's time to call your doctor.

What Is Pneumovax 23?

Pneumovax 23 (pneumococcal vaccine polyvalent) is a vaccine made by Merck that protects against 23 types of Streptococcus pneumoniae bacteria. These bacteria can cause serious infections including pneumonia, meningitis, and bloodstream infections (bacteremia). The vaccine is recommended for adults 50 and older and for people aged 2 and up who are at increased risk due to chronic illness or weakened immune systems.

For a deeper look at how the vaccine works, see our guide on how Pneumovax 23 works. For full details on uses and dosing, read What Is Pneumovax 23?

Common Side Effects

The most frequently reported side effects of Pneumovax 23 are mild and typically appear within hours of vaccination. They usually resolve within 1–3 days without treatment.

• Injection site pain, redness, swelling, or warmth — This is the most common reaction, affecting up to 60–80% of people who receive the vaccine. It's a normal sign that your immune system is responding.
• Fatigue or tiredness — Feeling more tired than usual for a day or so is common after vaccination.
• Headache — Mild to moderate headaches may occur.
• Muscle pain (myalgia) — General achiness, especially in the arm where the shot was given.
• Low-grade fever — A slight increase in body temperature (below 102°F) is a normal immune response.
• Joint pain — Some people experience mild joint discomfort.

These side effects are generally more noticeable with revaccination (a second dose). If you've had Pneumovax 23 before and are getting a booster dose, the injection site reaction may be somewhat stronger than the first time.

Serious Side Effects

Serious side effects from Pneumovax 23 are rare, but it's important to know what to watch for:

• Severe allergic reaction (anaphylaxis) — Signs include difficulty breathing, swelling of the face or throat, rapid heartbeat, dizziness, and hives. This is extremely rare but can be life-threatening. It usually occurs within minutes of vaccination, which is why you're asked to wait 15 minutes after the shot.
• High fever (above 102°F) — While a low-grade fever is normal, a high fever is not typical and should be reported to your doctor.
• Severe injection site reaction — If the redness, swelling, or pain at the injection site is severe, spreading, or getting worse after 48 hours, it could indicate a cellulitis-like reaction that needs medical attention.
• Febrile seizures — Very rare and primarily a concern in young children, not adults.
• Guillain-Barré syndrome (GBS) — An extremely rare neurological condition involving muscle weakness or paralysis. A causal link to Pneumovax 23 has not been established, but it has been reported after vaccination in very rare cases.

When to Call Your Doctor

Contact your healthcare provider or seek medical attention if you experience:

• Signs of a severe allergic reaction (difficulty breathing, swelling of face/lips/throat, hives, rapid pulse)
• Fever above 102°F that doesn't come down with acetaminophen or ibuprofen
• Injection site redness or swelling that is spreading, worsening, or hasn't improved after 3 days
• Unusual weakness, numbness, or tingling in your arms or legs
• Any symptom that feels severe or concerns you

If you think you're having a severe allergic reaction, call 911 or go to the nearest emergency room immediately.

Side Effects in Specific Populations

Older Adults (65+)

Side effects in older adults are generally similar to those in younger adults. However, older adults may have a somewhat weaker immune response to the vaccine, which can mean milder side effects but also potentially less robust protection.

Immunocompromised Patients

People with weakened immune systems — including those with HIV, cancer, organ transplants, or those taking immunosuppressive medications — can safely receive Pneumovax 23. Side effects are similar, though the immune response (and therefore some side effects) may be diminished. These patients are among those most likely to need the vaccine, as they face the highest risk from pneumococcal disease.

Children (Ages 2+)

Pneumovax 23 is approved for high-risk children aged 2 and older. Side effects in children are similar to those in adults, with injection site reactions being the most common. Febrile seizures, while very rare, are slightly more of a concern in young children with high fevers.

Pregnant and Breastfeeding Women

Pneumovax 23 should only be given during pregnancy if clearly needed. There is limited data on use in pregnant women. The vaccine is considered safe for breastfeeding women.

How to Manage Common Side Effects

Most side effects don't require treatment, but these tips can help you feel more comfortable:

• Injection site pain or swelling: Apply a clean, cool, damp cloth to the area. Avoid rubbing the injection site.
• Headache or muscle pain: Over-the-counter pain relievers like acetaminophen (Tylenol) or ibuprofen (Advil, Motrin) can help. Follow the dosing instructions on the label.
• Fatigue: Rest and stay hydrated. Plan to take it easy for the rest of the day if possible.
• Low-grade fever: Stay hydrated, dress in lightweight clothing, and take acetaminophen or ibuprofen if needed.

Avoid strenuous exercise with the vaccinated arm for 24 hours. Most people feel completely back to normal within 1–2 days.

Final Thoughts

Pneumovax 23 is a well-established vaccine with a long safety record. The most common side effects — injection site soreness, mild fatigue, and low-grade fever — are temporary and a sign that your immune system is building protection against 23 types of pneumococcal bacteria. Serious reactions are extremely rare.

If you haven't gotten your pneumococcal vaccine yet, don't let concerns about side effects stop you. The diseases Pneumovax 23 prevents — including pneumonia, meningitis, and bloodstream infections — are far more dangerous than any vaccine side effect. Talk to your doctor or pharmacist about whether Pneumovax 23 is right for you.

Looking for Pneumovax 23 near you? Search Medfinder to check availability at local pharmacies.