Unexpected Benefits from MMR Vaccine
Robert S. Baltimore, MD
Infants receiving MMR after three doses of DTaP-IPV-Hib had a significantly lower hospitalization rate for all infectious diseases than those receiving MMR before the third dose.
Measles, mumps, and rubella vaccine (MMR) is a live preparation designed to prevent these specific viral illnesses. Trials conducted in developing countries suggest that receipt of MMR also lowers risk for other infections. Investigators hypothesized that this effect might also be seen in higher-income countries — and that the effect would be greatest in children whose most-recent vaccine was MMR, rather than the inactivated diphtheria, tetanus, pertussis, polio, and Haemophilus influenzae b vaccine (DTaP-IPV-Hib).
In Denmark, the recommended infant vaccination schedule is three doses of DTaP-IPV-Hib, administered at 3, 5, and 12 months, followed by MMR at 15 months. Some children receive MMR before the third dose of DTaP-IPV-Hib3. With this reversed order, a child's most-recent vaccine, at ages 15 months to 2 years, is an inactivated one (DTaP-IPV-Hib3) and not a live-virus preparation.
The investigators obtained vaccination data from the Danish National Board of Health — and hospitalization data from the Danish National Patient Registry — for children born in Denmark between January 1, 1997, and August 31, 2006. A total of 456,043 children received the vaccines according to the recommended schedule and 19,219 (~4%) received them in reversed order. Hospitalization due to any infection was significantly less common in children immunized according to the recommended schedule than in those following the reversed schedule (8.9 vs. 12.4 admissions per 100 patient-years; adjusted incident rate ratio, 0.86; P<0.001). The effect for the cohort following the recommended schedule was seen for all major classes of infection but was most marked for lower respiratory tract infections.
Citation(s):
Sørup S et al. Live vaccine against measles, mumps, and rubella and the risk of hospital admissions for nontargeted infections. JAMA 2014 Feb 26; 311:826.
