Do Combination Vaccines or Simultaneous Vaccination Increase the Risk of Adverse Events?

Abstract

Certain combination vaccines or simultaneous administration of vaccines that are known to cause fever can rarely cause febrile seizures in infants and young children beyond the risk presented by individually administered vaccines. Specifically, the rate of febrile seizures in the 7-10 days after vaccination was approximately 2-3 times higher for children who received MMRV as compared to MMR and varicella vaccines administered separately on the same day and 4 times higher as compared to MMR alone, and when influenza and pneumococcal conjugate vaccines are given simultaneously as opposed to separately in children 6-59 months of age, the risk of febrile seizures in the 24 hours after vaccination increases from roughly 5 to 17.5 per 100,000 doses. Simultaneous administration of Tdap and influenza vaccines during pregnancy does not increase the risk of acute adverse events or adverse birth outcomes. Combination vaccines and simultaneous administration of vaccines currently routinely recommended to the general population in the U.S. have not been shown to cause any other adverse events at a greater rate than their individual vaccine components.