Positive rates for rubella antibody in pregnant women and benefit of post‐partum vaccination in a Japanese perinatal center

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Abstract
Aim: This study of pregnant women was undertaken to clarify their immune status for rubella and to evaluate the efficacy of, and adverse reaction to, post‐partum rubella vaccination. Methods: We determined the levels of both rubella antibody by hemagglutination inhibition test and IgM antibody by enzyme‐linked immunosorbent assay in the first gestational trimester and surveyed the positive rates for rubella antibody in pregnant women at our perinatal center; we recommended post‐partum vaccination for women with poor immune status. We also evaluated the effectiveness of the vaccine and any adverse reaction. Results: Among 2741 pregnant women, 185 cases (6.7%) were seronegative for rubella virus. This rate was especially high (12.4%) in the population who had opted out of the vaccination because of a change in Japanese government policy. A total of 30 cases (1.1%) were positive or false‐positive for IgM antibody, but no congenital rubella syndrome (CRS) developed. The seropositive rate was 93.3% in total, but this figure includes those who required post‐partum vaccination (558 cases or 20.3%) because their titers were 16× or lower. Among 145 cases who received post‐partum rubella vaccine, no severe adverse reaction was detected, and in all 37 cases with hemagglutination inhibition antibody titers of 8× or lower, the efficacy rate was 100%. Conclusions: It is necessary to appropriately evaluate the CRS risk. Also, we need to emphasize the importance and safety of post‐partum rubella vaccination in Japan.