Case-Control Evaluation of the Effectiveness of the G1P[8] Human Rotavirus Vaccine during an Outbreak of Rotavirus G2P[4] Infection in Central Australia

Abstract

The human rotavirus vaccine was evaluated during an outbreak of rotavirus G2P[4] infection in central Australia. No overall protective effect against hospitalization was demonstrated, raising concerns over the durability of vaccine protection against heterotypic strains. Two and a half years after commencing routine vaccination with human rotavirus vaccine, an outbreak of rotavirus G2P[4] infection occurred in central Australia. Vaccine effectiveness against a P[8]-containing strain (G9P[8]) had been demonstrated previously in this setting. This subsequent outbreak provided the opportunity to evaluate vaccine effectiveness against hospitalizations for a non-vaccine-related genotype in the same population. A case-control study was nested within a cohort of vaccine-eligible children listed on a population-based immunization register. Children with rotavirus-confirmed gastroenteritis were individually matched by date of birth and Indigenous status with 4 control subjects. Forty-one cases met the inclusion criteria, and 21 were severe cases among infants aged <12 months. Nineteen (46%) of 41 case patients had received 2 doses of human rotavirus vaccine, compared with 87 (53%) of 164 control subjects. Vaccine effectiveness against rotavirus-related hospitalization was 19% (odds ratio, .81; 95% confidence interval, .32-2.05) for 2 doses compared with none. On secondary analysis, there was evidence of a protective effect against disease complicated by acidosis in the subset of infants aged <12 months (odds ratio, .15; 95% confidence interval, .03-.84). Evidence was not found for an overall protective effect of human rotavirus vaccine against hospitalization for rotavirus disease in this setting. Post hoc analyses suggested a protective effect against severe disease in young infants.