Early MMR Vaccination is not linked to Reduction in Hospitalizations for Non-Targeted Infections in Infants: BMJ study

Vaccines protect against targeted infections. The current hypothesis states that live attenuated vaccines containing the measles virus, besides generating specific protection, also provide general beneficial health effects like decreased risk of morbidity and mortality. In contrast, inactivated vaccines, like combined diphtheria, tetanus, and pertussis vaccine, have detrimental effects.

The main objective of this study was to test for potential non-specific effects of an additional, early measles, mumps, and rubella (MMR) vaccine at age 5-7 months on the risk of infection-related hospitalization before age 12 months in a randomized, double-blinded, placebo-controlled trial, including 6540 Danish infants aged 5 to 7 months.

Researchers allocated Infants in 1:1 to intramuscular injection with standard titre MMR vaccine (M-M-R VaxPro) or placebo (solvent only).

In Denmark, the first three doses of DTaP-IPV-Hib+PCV are scheduled at 3, 5, and 12 months of age—that is, the first two doses were administered before randomization and the third dose at the end of follow-up. To account for a possible effect of diphtheria, tetanus, and pertussis as the latest administered vaccine, we performed an analysis where the infants were censored at the date of immunization with DTaP-IPV-Hib+PCV after randomization.

The study results are:

• Six thousand five hundred thirty-six infants were included.
• Three thousand two hundred sixty-four infants randomized to the MMR vaccine experienced 786 hospitalizations for infection before age 12 months compared with 762 for the 3272 infants randomized to placebo.
• There was no difference in the rate of hospitalizations for infection between the MMR vaccine and placebo groups.
• For infants randomized to the MMR vaccine compared with those randomized to placebo, the hazard ratio of hospitalizations for infection with a duration of at least 12 hours and prescriptions of antibiotics was 1.25 and 1.04, respectively.
• The estimate did not change when censoring at the date infants received DTaP-IPV-Hib+PCV after randomization (1.02, 0.90 to 1.16).

The primary outcome of our study was hospitalizations for infection, they said.

We found that live attenuated MMR vaccine administered to infants at 5-7 months of age did not decrease the rate of hospitalizations for non-targeted infection before age 12 months, they concluded.

The study’s strengths were a randomized controlled design, complete follow-up, and less risk of bias.

Further reading:

https://www.bmj.com/content/381/bmj-2022-072724