How Long Does Fever Last After a Baby Gets the Flu Shot?

Getting an annual flu vaccine is one of the most effective ways to protect infants and young children from seasonal influenza. While the flu shot is generally safe and well-tolerated, some babies may experience mild side effects after vaccination. Among these, a low-grade fever is one of the most commonly reported reactions, typically indicating that the immune system is responding appropriately to the vaccine.

Understanding Post-Vaccination Fever in Infants

It's not uncommon for babies to develop a slight fever within 24 hours after receiving the influenza vaccine. This reaction is usually mild and short-lived. In most cases, the elevated temperature lasts no more than 24 to 48 hours. The fever is typically low-grade (below 100.4°F or 38°C) and does not interfere with the child's normal activities or mood.

When to Monitor and When to Seek Help

If your baby develops a fever but remains cheerful, continues to eat normally, and shows no signs of discomfort, special treatment is usually unnecessary. Simple measures like ensuring proper hydration, dressing the baby in light clothing, and using a lukewarm sponge bath can help manage mild symptoms.

However, if the fever persists beyond two days or reaches a high level (above 102°F or 39°C), it's important to consult a licensed pediatrician. Prolonged fever may not be related to the vaccine and could indicate an underlying infection or another medical condition that requires evaluation.

Signs That Warrant Medical Attention

Watch for additional symptoms such as persistent crying, rash, difficulty breathing, lethargy, vomiting, or loss of appetite. These could signal something other than a typical vaccine response. A healthcare provider can perform a thorough assessment to determine whether the fever is vaccine-related or caused by a coincidental illness, especially during cold and flu season when other viruses are circulating.

In summary, a brief, mild fever after the flu shot is a normal part of the body's immune response in many infants. With proper observation and care, most babies recover quickly without complications. Always keep track of symptoms and maintain open communication with your pediatrician to ensure your child stays healthy and protected.