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BACKGROUND. In a Latin American trial, a monovalent G1P8 rotavirus vaccine showed high efficacy against severe rotavirus diarrhea. Protection was lower against serotypically unrelated G2P4 strains, which circulated infrequently. This case-control study was undertaken to assess the effectiveness of this monovalent G1P8 rotavirus vaccine against G2P4 strains in Brazil. METHODS. Case patients were children with severe G2P4 rotavirus diarrhea who presented at a hospital in Recife, Brazil, from March 2006 through September 2008. Vaccination rates among case patients were compared with rates among 2 groups of control participants-children with rotavirus-negative diarrhea and children admitted for acute respiratory tract infection (ARI)-to calculate vaccine effectiveness, after controlling for the birth month and year. RESULTS. We enrolled 70 G2P4 rotavirus-positive case patients with severe diarrhea, 484 rotavirus-negative control participants with diarrhea, and 416 control participants with ARI, aged 6 months. Among children aged 6-11 months, the effectiveness of the vaccine against G2P4 diarrhea was 77% (95% confidence interval CI, 42%-91%) and 77% (95% CI, 43%-90%) among the rotavirus-negative control participants with diarrhea and control participants with ARI, respectively. Vaccine effectiveness in children aged 12 months decreased to -24% (95% CI, -190% to 47%) and 15% (95% CI, -101 to 64) among the rotavirus-negative control groups with diarrhea and ARI, respectively. CONCLUSIONS. This monovalent G1P8 rotavirus vaccine was effective against severe G2P4 rotavirus diarrhea among children aged 6-11 months. Effectiveness declined among children aged 12 months, which suggests waning immunity.
Correia et al. (Mon,) studied this question.