Which vaccines cannot be given together in pediatric patients?

Which Vaccines Cannot Be Given Together in Children

In children, live parenteral vaccines (MMR, varicella, MMRV, yellow fever) are the only vaccines that cannot be given together if not administered on the same day—they must be separated by at least 4 weeks. All inactivated vaccines can be given simultaneously with each other and with live vaccines without restriction. 1, 2

Live Parenteral Vaccine Spacing Requirements

The critical restriction involves live parenteral vaccines administered on different days:

• If two live parenteral vaccines (MMR, varicella, MMRV, yellow fever) are not given simultaneously on the same day, they must be separated by ≥4 weeks (28 days). 1, 2
• Administering a second live parenteral vaccine within 28 days of the first (rather than simultaneously or ≥4 weeks apart) results in impaired immune response to the second vaccine. 1, 2
• The vaccine administered second should not be counted as valid if given <4 weeks after the first live vaccine and must be repeated ≥4 weeks after the invalid dose. 1

Important exception: Oral live vaccines (oral polio vaccine, oral typhoid Ty21a) can be given at any interval before, with, or after parenteral live vaccines without restriction. 1

All Other Vaccines Can Be Given Together

Inactivated vaccines have no spacing restrictions:

• All inactivated vaccines (DTaP, hepatitis A, hepatitis B, influenza, pneumococcal, HPV, COVID-19) can be administered simultaneously with each other at any time. 1, 2, 3, 4
• Inactivated vaccines can be given at any interval before, with, or after live vaccines without interference. 1, 2

Live parenteral vaccines given on the same day are acceptable:

• MMR and varicella can be administered simultaneously at different anatomic sites on the same day. 1
• All routine childhood vaccines (DTaP, MMR, IPV, Hib, hepatitis B, varicella) can be given together at the same visit at separate sites. 2, 5, 6

Critical Pitfalls to Avoid

The most common error is giving two live parenteral vaccines 1-27 days apart:

• A study showed children who received varicella vaccine <30 days after MMR (but not on the same day) had a 2.5-fold increased risk of vaccine failure compared to those who received varicella before or >30 days after MMR. 1
• Solution: Either give live vaccines on the same day at different sites, or separate them by ≥4 weeks. 1, 2

Never mix vaccines in the same syringe unless FDA-approved:

• Only one combination (DTaP and PRP-T Hib vaccine, TriHIBit®) is FDA-approved for mixing in the same syringe, and this should not be used for primary vaccination in infants aged 2,4, and 6 months. 1
• All other vaccines must be administered at separate anatomic sites. 2, 4

Special Considerations for MMRV Vaccine

For the first dose at age 12-47 months, separate MMR and varicella vaccines are preferred over MMRV:

• MMRV vaccine has a higher risk of febrile seizures after the first dose compared to separate MMR and varicella vaccines given at the same visit. 1
• For the second dose at any age (15 months-12 years) and for the first dose at age ≥48 months, MMRV is generally preferred over separate injections. 1
• Children with personal or family history of seizures should receive separate MMR and varicella vaccines rather than MMRV. 1