High residual prevalence of vaccine-serotype Streptococcus pneumoniae carriage after introduction of a pneumococcal conjugate vaccine in Malawi: a prospective serial cross-sectional study

Todd D. Swarthout, Claudio Fronterre, José Lourenço, Uri Obolski, Andrea Gori, Naor Bar-Zeev, Dean Everett, Arox W. Kamng’ona, Thandie S. Mwalukomo, Andrew A. Mataya, Charles Mwansambo, Marjory Banda, Sunetra Gupta, Peter Diggle, Neil French, Robert S. Heyderman

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Jun 25, 2019
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Received Date: 20th June 19

Background

There are concerns that pneumococcal conjugate vaccines (PCV) in sub-Saharan Africa sub-optimally interrupt vaccine-serotype (VT) carriage and transmission, thus limiting vaccine-induced direct and indirect protection. We assessed carriage in vaccinated children and unvaccinated populations targeted for indirect protection, between 4 and 7 years after Malawi’s November 2011 introduction of PCV13 using a 3+0 schedule.

 

Methods

We conducted sequential prospective nasopharyngeal carriage surveys between 2015 and 2018 among healthy PCV-vaccinated and PCV-unvaccinated children, and HIV-infected adults. VT and NVT carriage risk by age was analysed by non-linear regression.

 

Results

Among PCV-vaccinated children, there was a 24% relative reduction in carriage, from a mean 21.1% to 16.1%; 45% reduction among older PCV-unvaccinated children, from 27.5% to 15.2%; 41.4% reduction among adults, from 15.2% to 8.9%. Using carriage data from children 3.6 to 10 years of age, VT carriage probability declined with age, with a similar prevalence half-life among PCV-vaccinated (3.34 years) and PCV-unvaccinated (3.26 years) children.

 Conclusion

Compared to high-income settings, the 3+0 schedule in Malawi has led to a sub-optimal reduction in pneumococcal carriage prevalence. This is likely due to recolonisation of vaccinated children with waning vaccine-induced immunity, resulting in insufficient indirect protection of unvaccinated populations. Rigorous evaluation of strategies to augment vaccine-induced control of carriage, including alternative schedules and catch-up campaigns is required.

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This is an abstract of a preprint hosted on an independent third party site. It has not been peer reviewed but is currently under consideration at Nature Communications.

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