Serotype replacement in disease after pneumococcal vaccinationArchived

ECDC comment

The heptavalent pneumococcal conjugate vaccine (PCV7) targets seven of the more than 92 pneumococcal serotypes. Concerns have been raised that non-vaccine serotypes (NVTs) could increase in prevalence and reduce the benefits of vaccination. Indeed, among asymptomatic carriers, the prevalence of NVTs has increased substantially, and consequently, there has been little or no net change in the bacterial carriage prevalence.

Weinberger D, Malley R, Lipsitch M. The Lancet - 13 April 2011 DOI: 10.1016/S0140-6736(10)62225-8

In many populations, pneumococcal disease caused by NVT has increased, but in most cases this increase has been less than the increase in NVT carriage. In this review, the authors discuss the evidence for serotype replacement in carriage and disease, and address the surveillance biases that might affect these findings. They then discuss possible reasons for the discrepancy between near-complete replacement in carriage and partial replacement for disease, including differences in invasiveness between vaccine serotypes. The authors contend that the magnitude of serotype replacement in disease can be attributed, in part, to a combination of lower invasiveness of the replacing serotypes, biases in the pre-vaccine carriage data (unmasking), and biases in the disease surveillance systems that could underestimate the true amount of replacement. They conclude by discussing the future potential for serotype replacement in disease and the need for continuing surveillance.