MMR vaccination led to fewer hospitalizations among children

Receipt of a live vaccine against measles-mumps-rubella as the most recent vaccination was associated with fewer hospitalizations for common infections — particularly for lower respiratory tract infections — among children living in a high-resource setting, according to new study data published in JAMA.

“It is important to administer the MMR vaccine at the recommended age,” Signe Sørup, PhD, of the Research Center for Vitamins and Vaccines at the Statens Serum Institute, Copenhagen, Denmark, told Infectious Disease News. “It is well recognized that MMR is important for protection against measles, mumps and rubella. Our study adds that MMR may have a general immune stimulating effect preventing some hospital admissions for unrelated infections. Potentially the results could be used as an additional incentive for parents to bring their children for MMR vaccination on time.”

Signe Sørup

The researchers analyzed data from Danish national registers on 495,987 children born in Denmark between 1997 and 2006, when the recommended vaccination schedule consisted of three doses of inactivated vaccine against diphtheria, tetanus, pertussis, polio and Haemophilus influenza type b (DTaP-IPV-Hib) administered at ages 3, 5 and 12 months, and MMR at 15 months. The cohort was followed up to age 2 years.

The researchers calculated the incidence rate ratios (IRRs) of hospital admissions associated with any type of infection, comparing children who had received the MMR as the most recent vaccine with children who had not yet received MMR and therefore had DTaP-IPV-Hib as their most recent vaccination. The researchers controlled for potential confounding variables, which had little effect on the results.

Among the entire cohort, there were 56,889 hospitalizations for any type of infection. The rate of admission for infection was significantly lower among children who received the live MMR vaccine after receiving three doses of inactivated DTaP-IPV-Hib vaccine (IRR=0.86; 95% CI, 0.84-0.88) vs. children who received three doses of DTaP-IPV-Hib only.

Among children aged 16 to 24 months, the risk for hospitalization for an infection was 4.6% (95% CI, 4.5-4.7) for those who received the MMR vaccine on time and 5.1% (95% CI, 5-5.2) for those who did not, a difference of 0.5 percentage points (95% CI, 0.4-0.6). The number needed to vaccinate with MMR before the age of 16 months to prevent one hospital admission was 201 (95% CI, 159-272).

Although MMR vaccination protected against hospitalization for any infection type, the association was strongest for lower respiratory tract infections (IRR=0.8; 95% CI, 0.76-0.84).

“The high-quality data, the strict control for confounders, and the consistency with prior observations from low-income countries all support that vaccines also have [nonspecific] effects on susceptibility to infections in high-income countries,” the researchers wrote.

In an accompanying editorial, David Goldblatt, MBChB, PhD, of the immunobiology unit at the University College London’s Institute of Child Health, and Elizabeth Miller, FRCPath, of the hepatitis and blood safety department at Public Health England, wrote that there have been no prospective studies on the immunological mechanisms behind the reduced risk for infections.

“Although reanalysis of the available evidence is important, the ability to properly control for bias and confounding in observational studies is often limited, and without randomized controlled trials specifically designed to test the hypothesis, the issue of nonspecific effects of vaccines may remain subject to continuing debate,” they concluded. – by John Schoen

Signe Sørup, PhD can be reached at sgs@ssi.dk.

For more information:

Goldblatt D. JAMA. 2014;311:804-805.

Sørup S. JAMA. 2014;311:826-835.

Disclosure: One of the researchers reported owning a private statistical consultancy.