Determining the pneumococcal conjugate vaccine coverage required for indirect protection against vaccine-type pneumococcal carriage in low and middle-income countries: a protocol for a prospective observational study

Abstract

IntroductionPneumococcal conjugate vaccines (PCVs) prevent disease through both direct protection of vaccinated individuals and indirect protection of unvaccinated individuals by reducing nasopharyngeal (NP) carriage and transmission of vaccine-type (VT) pneumococci. While the indirect effects of PCV vaccination are well described, the PCV coverage required to achieve the indirect effects is unknown. We will investigate the relationship between PCV coverage and VT carriage among undervaccinated children using hospital-based NP pneumococcal carriage surveillance at three sites in Asia and the Pacific.Methods and analysisWe are recruiting cases, defined as children aged 2–59 months admitted to participating hospitals with acute respiratory infection in Lao People’s Democratic Republic, Mongolia and Papua New Guinea. Thirteen-valent PCV status is obtained from written records. NP swabs are collected according to standard methods, screened using lytA qPCR and serotyped by microarray. Village-level vaccination coverage, for the resident communities of the recruited cases, is determined using administrative data or community survey. Our analysis will investigate the relationship between VT carriage among undervaccinated cases (indirect effects) and vaccine coverage using generalised estimating equations.Ethics and disseminationEthical approval has been obtained from the relevant ethics committees at participating sites. The results are intended for publication in open-access peer-reviewed journals and will demonstrate methods suitable for low- and middle-income countries to monitor vaccine impact and inform vaccine policy makers about the PCV coverage required to achieve indirect protection.

Effect of ten-valent pneumococcal conjugate vaccine introduction on pneumococcal carriage in Fiji: results from four annual cross-sectional carriage surveys

“…The degree of indirect effects is likely to be associated with the coverage achieved. 31 The results of this study are consistent with a systematic review that found that carriage of vaccine serotypes declined in non-target age groups after PCV introduction. 11 Reductions in vaccine-type carriage occurred contemporaneously with reductions in vaccine-type invasive pneumococcal disease, supporting the usefulness of carriage as an alternative for disease surveillance to show the population effects of PCV.…”

Indirect effects of 13-valent pneumococcal conjugate vaccine on pneumococcal carriage in children hospitalised with acute respiratory infection despite heterogeneous vaccine coverage: an observational study in Lao People’s Democratic Republic

“…This analysis was part of a multi-site study across the Asia-Pacific region examining the relationship between PCV13 coverage and indirect effects in Lao PDR, Mongolia and Papua New Guinea. 9 The Lao PDR component was embedded within a prospective hospital-based study of the aetiology of ARI. 23 We used the same terminology outlined by Halloran et al in which indirect effects are defined as the population-level effects of a vaccination strategy experienced by individuals regardless of vaccination status.…”

Immunization: vital progress, unfinished agenda

“…Community or herd immunity is an important consideration when estimating the full public health value of immunization. The threshold to achieve such community protection can be as high as 95% for measles, but as low as 80% for rubella, and 60% in high-income settings for the effect to begin for pneumococcal vaccination, which means that the programme strength required to derive additional impact varies substantially by vaccine [11][12][13] . These differences in the required critical vaccination coverage rates are due to the basic reproductive ratio of an infection (R 0 ) 14 , which can vary greatly among various infectious diseases.…”