Evaluations of vaccine effectiveness conducted in Burkina Faso, Malawi, and Tanzania reaffirm the moderate efficacy of rotavirus vaccines against moderate-to-severe diarrhea in these countries, with a trend toward diminished effectiveness after the first year of life. Burkina Faso introduced pentavalent rotavirus vaccine in October 2013 with 3 doses given at 2, 3, and 4 months of age. In vaccine-eligible children ≥6 months of age in Burkina Faso, a full series of vaccine was 35% (95% confidence interval (CI): −15%, 63%) effective against rotavirus hospitalizations.[22] When restricting the analysis to children 6–11 months of age, a full course of vaccine was 58% (95% CI: 10%, 81%) effective but effectiveness dropped to 19% (95% CI: −78%, 65%) in children 12 months of age and older. A similar pattern of declining effectiveness in older children was also seen in Malawi which introduced monovalent rotavirus vaccine in October 2012 with 2 doses given at 6 and 10 weeks of age.[23] Among all vaccine-eligible children, vaccine effectiveness was 62% (95% CI: 28%, 80%) against rotavirus hospitalizations in Malawi but when stratifying by age, the vaccine was 86% (95% CI: 59%, 95%) effective in children <12 months of age and 32% (95% CI: −139%, 80%) in children 12–23 months of age. In January 2013, Tanzania also introduced monovalent rotavirus vaccine with a 2 dose schedule at 6 and 10 weeks of age. In three hospitals in northwest Tanzania, at least one dose of rotavirus vaccine was 53% (95% CI: −14%, 81%) effective against rotavirus hospitalizations in children 5–23 months of age.[24] When the analysis was restricted to more severe disease outcomes, at least one dose of vaccine was 66% (95% CI: 9%, 87%) effective in children requiring IV rehydration and 70% (95% CI: 14%, 90%) effective against moderate-to-severe rotavirus disease (Vesikari score ≥11). Rotavirus vaccine effectiveness increased with increasing Vesikari score, consistent with clinical trial data that rotavirus vaccines are more efficacious against diarrhea of greater severity.[3, 4]

The evaluations included in this Special Issue of Vaccine provide further evidence of the tremendous health impact and effectiveness of rotavirus vaccination in sub-Saharan Africa. Countries that have introduced rotavirus vaccine into their national immunizations program have documented a decline in the proportion of diarrhea hospitalizations due to rotavirus and a decline in total hospitalizations due to diarrhea among children <5 years of age. The greatest declines were seen in children <1 year of age and the burden of disease may therefore be shifting to children >1 year of age. Vaccine effectiveness was similar to that seen in the clinical trials with some evidence of waning immunity after the first year of life. No single genotype has emerged as dominant in vaccine introducing countries. Rotavirus vaccine was shown to be high cost-effective in Ghana and will likely remain so even after Gavi support ends.

One commonality among many of the evaluations in this Special Issue is that many used an existing rotavirus surveillance platform to monitor trends in rotavirus hospitalizations over time and to serve as a platform upon which to build a vaccine effectiveness evaluation using standardized methods.[43, 44] These studies exemplify the importance of continuous, robust surveillance both before and after rotavirus vaccine introduction to document the impact of the vaccination program. In many settings, rotavirus surveillance was supplemented with a review of hospital discharge data for acute gastroenteritis hospitalizations. As rotavirus infection accounts for such a large proportion of acute gastroenteritis hospitalizations prior to vaccine introduction, monitoring trends in all-cause acute gastroenteritis also offers a broad perspective for rotavirus vaccine impact evaluations and a resource efficient complement to active rotavirus surveillance to monitor impact of vaccination.

Despite the promising findings reported in this Special Issue, further work still remains for evaluating rotavirus vaccines in sub-Saharan Africa. Nigeria and the Democratic Republic of Congo are on the threshold of rotavirus vaccine introduction and generating similar data on rotavirus vaccine performance in these countries with large birth cohorts will demonstrate that rotavirus vaccines can be successfully implemented in countries with complex immunization programs. Additional data on rotavirus vaccine effectiveness and impact is also needed from Francophone countries in Africa and countries with weaker immunization programs. Continued surveillance to document the long-term impact of rotavirus vaccination on disease trends and circulating rotavirus strains remains important. Several countries in Africa have noted a decline in in-hospital diarrhea deaths following rotavirus vaccine introduction but evidence of vaccine impact on overall diarrhea mortality among children under 1 and under 5 years of age is extremely limited. Rotavirus vaccine impact on overall diarrhea mortality could be investigated through population-based Health and Demographic Surveillance Systems. Earlier this year, a third rotavirus vaccines (ROTAVAC, Bharat Biotech) was pre-qualified by WHO and if any country in Africa introduces this vaccine into its national immunization program, monitoring its performance would be a priority as this vaccine has not been widely evaluated globally. Finally, as rotavirus disease declines in the region, it is important to assess how rotavirus vaccine introduction impacts overall diarrhea disease epidemiology, including etiology changes.

The evaluations conducted in the African region can serve as a model for other regions such as Asia where wide-scale rotavirus vaccine introductions are just beginning and surveillance is ongoing as part of the WHO-coordinated Global Rotavirus Surveillance Network. Furthermore, as countries begin transitioning from Gavi support, the findings of these studies provide evidence of the impact and effectiveness of rotavirus vaccination programs under conditions of routine use.