Vaccination herd effect experience in Latin America: a systematic literature review

ABSTRACT

Background: National pediatric vaccination programs have been introduced in Latin America (LatAm) to reduce the burden of diseases due to pathogens such as rotavirus, Haemophilus influenzae type b (Hib) and pneumococcus. Vaccination health benefits may extend to unvaccinated populations by reducing pathogen transmission. Understanding herd effect is important for implementation and assessment of vaccination programs. The objective was to conduct a systematic review of published epidemiological evidence of herd effect with Hib, rotavirus and pneumococcal conjugate vaccines (PCV) in LatAm.

Methods: Searches were conducted in PubMed, Virtual Health Library (VHL), SciELO and SCOPUS databases, for studies reporting data on herd effect from Hib, rotavirus and PCV vaccination in LatAm, without age restriction. Searches were limited to articles published in English, Spanish or Portuguese (1990–2016). After screening and full-text review, articles meeting the selection criteria were included to be critically appraised following criteria for observational and interventional studies. The presence of a herd effect was defined as a significant decrease in incidence of disease, hospitalization, or mortality.

Results: 3,465 unique articles were identified, and 23 were included (Hib vaccine n = 5, PCV n = 8, rotavirus vaccine n = 10). Most studies included children and/or adolescents (age range varied between studies). Studies in adults, including older adults (aged > 65 years), were limited. Few studies reported statistically significant reductions in disease incidence in age groups not targeted for vaccination. Hib-confirmed meningitis hospitalization decreased in children but herd effect could not be quantified. Some evidence of herd effect was identified for PCV and rotavirus vaccine in unvaccinated children. Evidence for herd effects due to PCV in adults was limited.

Conclusion: After introduction of Hib, PCV and rotavirus vaccination in LatAm, reductions in morbidity/mortality have been reported in children not targeted for vaccination. However, due to methodological limitations (e.g. short post-vaccination periods and age range studied), there is currently insufficient evidence to quantify the herd effect in adult populations. More research and higher quality surveillance is needed to characterize herd effect of these vaccines in LatAm.

Keywords:

• Haemophilus influenzae type b (Hib) vaccine
• herd effect
• Latin America
• pneumococcal conjugate vaccine
• rotavirus vaccine
• systematic review

Acknowledgments

Authors would like to thank Business & Decision Life Sciences platform for editorial assistance and publications coordination, on behalf of GSK. Pierre-Paul Prévot coordinated manuscript development and editorial support.The authors would also like to thank also Carole Nadin who provided medical writing assistance on behalf of GSK.

Disclosure of potential conflicts of interest

SA, DPC, JNG, MPR and EOB are employees of the GSK group of companies. RD was an employee of the GSK group of companies at the time the study was conducted. RD and JNG report holding shares in the GSK group of companies as part of their employee remuneration. EB and JE reports grants from the GSK group of companies.

Trademarks

Rotarix is a trademark of GSK group of companies.

Avaibility of data and materials

All data generated or analysed during this study are included in this published article and its supplementary information files.

Authors’ contributions

All authors participated in the design or implementation or analysis, and interpretation of the study. EB, JE, RD and SA perform the search literature. EB and JE reviewed inclusion and exclusion criteria and complete data extraction. All authors had full access to the data and participated in the development of the manuscript, revised it critically for important intellectual content, approved the final version before submission, and agreed to be accountable for all aspects of the work.

Supplementary Material

Supplemental data for this article can be accessed here.

Additional information

Funding

GlaxoSmithKline GSK Biologicals SA funded this study (GSK Study identifier: HO-15-16768) and was involved in all stages of study conduct, including analysis of the data. GlaxoSmithKline GSK Biologicals SA also covered all costs associated with the development and publication of this manuscript.