Yes, Flu Shot and Varicella Vaccine Can Be Given Together at 15 Months
Yes, you can and should administer the influenza vaccine simultaneously with the varicella vaccine to a 15-month-old child. This practice is safe, effective, and explicitly recommended by major pediatric guidelines.
Evidence Supporting Simultaneous Administration
Monovalent varicella vaccine may be administered simultaneously with other vaccines recommended for children 12 to 15 months of age, including influenza vaccine. 1 This recommendation is based on the principle that simultaneous administration of most widely used live-antigen and inactivated-antigen vaccines produces seroconversion rates and adverse reaction rates similar to those observed when vaccines are administered separately. 1
Direct Research Evidence
A high-quality randomized controlled trial specifically evaluated this exact scenario in 1,245 children aged 12-15 months. 2 The study found:
- Concurrent administration of live attenuated influenza vaccine with varicella vaccine provided equivalent immunogenicity compared with separate administration 2
- Seroresponse rates for varicella vaccine were ≥82% regardless of whether influenza vaccine was given simultaneously 2
- The incidences of reactogenicity events and adverse events were similar whether vaccines were given together or separately 2
- The combination was well tolerated 2
Additional research confirms that concomitant administration of varicella vaccine with other vaccines (including Hib and hepatitis B) at the 12- or 15-month visit is well-tolerated and suitably immunogenic. 3
Clinical Benefits of Simultaneous Administration
Administering all indicated vaccines at the same visit increases the likelihood of complete vaccination and provides timely protection. 4 This is particularly important because:
- The immune response to one vaccine is not negatively affected by another vaccine when administered simultaneously 4
- Simultaneous administration is crucial if there's any possibility the child might not return for subsequent vaccinations 1
- Research shows that approximately one-third of measles cases among unvaccinated preschool children could have been prevented if vaccines had been administered simultaneously during previous visits 1, 5
Practical Administration Guidelines
When giving both vaccines:
- Administer at separate anatomical sites 1, 5
- Never mix vaccines in the same syringe unless specifically FDA-approved for mixing 1, 4
- The varicella vaccine should be administered subcutaneously 1
- The influenza vaccine should be given according to its formulation (intramuscular for inactivated vaccine, intranasal for live attenuated vaccine if age-appropriate) 6
Important Caveats
Defer vaccination if the child has:
- Moderate to severe acute illness 4
- Immunodeficiency conditions 1
- Severe allergic reactions to vaccine components 1
- Recent receipt of antibody-containing products (may affect varicella vaccine response) 1
Document all vaccines administered in the child's permanent medical record and provide the parent with an updated immunization record. 4