Adherence to vaccine schedule may lower rate of infection-related hospitalization
It appears that healthy vaccinee bias partially explains the observed lower rate of hospitalization for infection after measles, mumps and rubella (MMR) vaccination, according to a recent study. This lower rate correlates with receipt of any additional vaccine, not specifically MMR vaccine.
“In our observational study on nonspecific effects of vaccination in more than a million Dutch children, a lower rate of hospital admission for infection followed receipt of an additional vaccination (and therefore adherence to the routinely recommended schedule) and could not be attributed to MMR specifically,” researchers said.
A nationwide population-based cohort study was conducted involving 1,096,594 Dutch children born in 2005 to 2011 who received the first four diphtheria, tetanus, pertussis, polio, Haemophilus influenzae type b plus pneumococcal vaccines (DTaP-IPV-Hib+PCV).
In the Netherlands, DTaP-IPV-Hib+PCV is recommended at ages 2, 3, 4 and 11 months and MMR plus meningococcal C (MenC) vaccination at age 14 months. Researchers linked data from the national vaccine register to hospital admission data.
“Receipt of MMR+MenC as most recent vaccination was associated with a 38-percent lower rate of admission related to infectious disease, compared with DTaP-IPV-Hib+PCV as most recent vaccination,” according to researchers. “We also observed a 31-percent lower rate of admission for infection with receipt of the fourth DTaP-IPV-Hib+PCV as most recent vaccination, compared with the third as most recent vaccination.”
Children who had MMR+MenC as the most recent vaccination were likely to have a hazard ratio (HR) of 0.62 (95 percent CI, 0.57 to 0.67) for hospitalization due to infection and 0.84 (0.73 to 0.96) for injuries or poisoning, compared with the fourth DTaP-IPV-Hib+PCV as most recent vaccination. [BMJ 2017;358:j3862]
Furthermore, the fourth DTaP-IPV-Hib+PCV as most recent vaccination correlated with an HR of 0.69 (0.63 to 0.76) for hospital admission due to infection, compared with the third DTaP-IPV-Hib+PCV as most recent vaccination.
“These findings, together with those for the negative control outcome, suggest that the delay of a vaccination, be it DTaP-IPV-Hib+PCV or MMR+MenC, might depend on the health status of a child, rather than the other way around,” according to researchers. “We cannot exclude the presence of nonspecific effects of MMR vaccination, but we are unable to disentangle the possible nonspecific effects from bias.”
Nonspecific effects of vaccines containing measles on all-cause mortality have also been investigated in several randomized controlled trials (RCTs) in low-income countries. The pooled relative risk from four RCTs was 0.74 (0.51 to 1.07), suggesting the beneficial effects of receiving such vaccines. [BMJ 2016;358:i5170]
Similar to these vaccines, another live attenuated vaccine, BCG vaccination, has also been correlated with nonspecific effects in low-income countries. However, a recently published RCT on BCG vaccination at birth in Denmark did not find an effect on all-cause hospitalization or childhood infections. [BMJ 2016;358:i5170; Arch Dis Child 2017;358:224-31; Pediatr Res 2016;358:681-5]
“Our findings emphasize the importance of interpreting findings from observational studies on nonspecific effects of vaccination with great caution,” the authors of the current study said.