Effect of the Ten-valent Pneumococcal Conjugate Vaccine on Invasive Pneumococcal Disease and Pneumonia in Infants Younger Than Ten Weeks of Age in Southern Mozambique: A Population-based Prospective Surveillance Study.

BACKGROUND

Mozambique introduced 10-valent-pneumococcal conjugate vaccine (PCV10) in 2013. We aimed to evaluate the indirect effect of PCV10 on invasive pneumococcal disease (IPD) and clinical severe pneumonia (CSP) in infants aged less than 10 weeks.

METHODS

Routine surveillance data for IPD and CSP among admitted infants less than 10 weeks of age were analyzed to compare IPD and CSP incidence using demographic surveillance data from pre- and post-PCV10 periods. IPD was defined as isolation of pneumococcus from blood or cerebrospinal fluid, and CSP according to World Health Organization criteria.

RESULTS

The incidence of IPD and CSP among infants less than 10 weeks decreased by 87% [incidence rate ratio (IRR): 0.13; 95% confidence interval (CI): 0.02-0.95] from 283/100,000 in the pre-PCV to 36/100,000 children year at risk (CYAR) post-PCV, and by 62% (IRR: 0.38; 95% CI: 0.27-0.52) from 4100/100,000 pre-PCV to 1550/100,000 CYAR post-PCV periods, respectively. Vaccine-type IPD incidence declined by 92% (IRR: 0.18; 95% CI: 0.02-1.34) from 205/100,000 pre-PCV to 36/100,000 CYAR post-PCV, though the reduction was not statistically significant. The mortality rate due to IPD among infants less than 10 weeks declined from 47/100,000 CYAR in the pre-PCV to 0 in the post-PCV period. Mortality due to CSP declined by 29% (IRR: 0.71; 95% CI: 0.34-1.50), from 457/100,000 CYAR in the pre-PCV to 324/100,000 in the post-PCV periods.

CONCLUSIONS

PCV10 introduction led to substantial declines in the incidence of IPD, CSP and associated mortality in infants too young to be vaccinated (less than 10 weeks) in Mozambique, suggesting indirect protection.