Background: We evaluated the immunogenicity of the pentavalent rotavirus vaccine (PRV) in two GAVIeligible
Asian countries, Bangladesh and Vietnam, nested in a larger randomized, double-blind, placebocontrolled
efficacy trial conducted over a two-year period from 2007 through 2009.
Methods: 2036 infants were randomly assigned, in a 1:1 ratio, to receive three oral doses of PRV or
placebo approximately at 6, 10, and 14 weeks of age. Concomitant use of EPI vaccines, including oral
poliovirus vaccine (OPV) and diphtheria-tetanus-whole cell pertussis (DTwP) vaccine, was encouraged
in accordance to the local EPI schedule. A total of 303 infants were evaluated for immunogenicity and
blood samples were collected before the first dose (pD1) and approximately 14 days following the third
dose (PD3). The seroresponse rates (≥3-fold rise from pD1 to PD3) and geometric mean titers (GMTs)
were measured for anti-rotavirus immunoglobulin A (IgA) and serum neutralizing antibody (SNA) to
human rotavirus serotypes G1, G2, G3, G4, and P1A, respectively.
Results: Nearly 88% of the subjects showed a
≥3-fold increase in serum anti-rotavirus IgA response in
the analysis of the two countries combined. When analyzed separately, the IgA response was lower in
Bangladeshi children (78.1% [95% CI: 66.0, 87.5]) than in Vietnamese children (97.0% [95% CI: 89.6, 99.6]),
with a PD3 GMT of 29.1 (units/mL) and 158.5 (units/mL), respectively. In the combined population, the
SNA responses to the individual serotypes tested ranged from 10 (G3) to 50 (G1) percentage points lower
than the responses shown in the developed countries. However, the SNA response to G3 in Vietnamese
subjects was 37.3% (95% CI: 25.8, 50.0), which was similar to the G3 response rate in developed countries.
Conclusions: Three oral doses of PRV were immunogenic in two GAVI-eligible Asian countries: Bangladesh
and Vietnam. The GMTs of both the serum anti-rotavirus IgA and SNA responses were generally higher
in Vietnamese than in Bangladeshi children. The SNA responses varied by individual serotypes and were
lower than the results from developed countries. The clinical significance of these observations is not
understood because an immune correlate of protection has not been established.