To investigate susceptibility to and factors associated with rubella infection among pregnant mothers and
to estimate the burden of congenital rubella infection (CRI) in Vietnam where rubella-containing vaccine
(RCV) is not included in the routine immunization programme, we conducted a prospective cohort study
in Nha Trang, Vietnam between 2009 and 2010. Rubella-specific immunoglobulin-M and
immunoglobulin-G were investigated in cord blood samples by enzyme immunoassay. Corresponding
clinical-epidemiological data were analyzed and the national congenital rubella syndrome (CRS)
incidence was estimated using modeling. We enrolled 1988 pairs of mothers aged 17-45 years and their
newborn babies. No mothers had received RCV. Multivariate analysis revealed that mothers aged 17-24
(aOR 2.5, 95% CI: 1.7-3.8) or 25-34 (1.4, 1.0-2.1) years were more likely to be susceptible than those
aged 35-45 years. Overall 28.9% (574/1988, 95% CI: 26.9-30.9%) of mothers were seronegative. The
CRI rate was 151 (95% CI: 0-322) per 100,000 live births. Modeling estimated that 3788 babies (95% CI:
3283-4143) were born with CRS annually in Vietnam with an overall CRS incidence of 234 (95% CI:
207-262) cases per 100,000 live births. A substantial proportion of women of childbearing age (WCBA)
are at risk of rubella infection during pregnancy and this can result in a high frequency of miscarriage or
burden of CRS across Vietnam. Prompt introduction of RCV into national immunization programme with
catch-up vaccination to children and WCBA will reduce CRI in Vietnam.