Population Impact and Effectiveness of Monovalent Rotavirus Vaccination in Urban Malawian Children 3 Years After Vaccine Introduction: Ecological and Case-Control Analyses

Abstract

Background: Rotavirus vaccines have been introduced in many low-income African countries including Malawi in 2012. Despite early evidence of vaccine impact, determining persistence of protection beyond infancy, the utility of the vaccine against specific rotavirus genotypes, and effectiveness in vulnerable subgroups is important.

Methods: We compared rotavirus prevalence in diarrheal stool and hospitalization incidence before and following rotavirus vaccine introduction in Malawi. Using case-control analysis, we derived vaccine effectiveness (VE) in the second year of life and for human immunodeficiency virus (HIV)-exposed and stunted children.

Results: Rotavirus prevalence declined concurrent with increasing vaccine coverage, and in 2015 was 24% compared with prevaccine mean baseline in 1997-2011 of 32%. Since vaccine introduction, population rotavirus hospitalization incidence declined in infants by 54.2% (95% confidence interval [CI], 32.8-68.8), but did not fall in older children. Comparing 241 rotavirus cases with 692 test-negative controls, VE was 70.6% (95% CI, 33.6%-87.0%) and 31.7% (95% CI, -140.6% to 80.6%) in the first and second year of life, respectively, whereas mean age of rotavirus cases increased from 9.3 to 11.8 months. Despite higher VE against G1P[8] than against other genotypes, no resurgence of nonvaccine genotypes has occurred. VE did not differ significantly by nutritional status (78.1% [95% CI, 5.6%-94.9%] in 257 well-nourished and 27.8% [95% CI, -99.5% to 73.9%] in 205 stunted children;P= .12), or by HIV exposure (60.5% [95% CI, 13.3%-82.0%] in 745 HIV-unexposed and 42.2% [95% CI, -106.9% to 83.8%] in 174 exposed children;P= .91).

Conclusions: Rotavirus vaccination in Malawi has resulted in reductions in disease burden in infants <12 months, but not in older children. Despite differences in genotype-specific VE, no genotype has emerged to suggest vaccine escape. VE was not demonstrably affected by HIV exposure or stunting.

Keywords: case-control; developing countries; population impact; rotavirus vaccine; vaccine effectiveness.

Figure 1.

Rotavirus (RV) prevalence in diarrheal stools at Queen Elizabeth Central Hospital, Blantyre, Malawi, 1997–2015.

Figure 2.

Three-year moving average of genotype-specific prevalence in rotavirus enzyme immunoassay–positive stools, 1999–2009 and 2011–2015.

Figure 3.

G1P[8] prevalence among rotavirus enzyme immunoassay–positive diarrheic stools at Queen Elizabeth Central Hospital, Blantyre, Malawi, 1 January 1999–31 December 2009 and January 2012–June 2015. Abbreviation: CI, confidence interval.

Figure 4.

Monthly cases of rotavirus at Queen Elizabeth Central Hospital, Blantyre, Malawi, 1 January 2012–30 June 2015. Abbreviation: RVV, rotavirus vaccine.

Figure 5.

Age at diarrheal episode by rotavirus status before (1 January 2012–28 October 2012) and after (29 October 2012–30 June 2015) monovalent rotavirus vaccine introduction.