Background/Objective: Maternal immunization is highly recommended, particularly in developed countries. However, its awareness among pregnant women in Japan remains low. This study aimed to assess the awareness and attitudes toward maternal immunization among pregnant women in Japan and to identify the factors that may promote its acceptance. Methods: We conducted a cross-sectional questionnaire survey among pregnant women attending antenatal checkups at nine facilities in Kanagawa Prefecture, Japan, from August 2024 to January 2025. The survey assessed knowledge and intention regarding maternal immunization for influenza, pertussis, respiratory syncytial virus (RSV), and group B streptococcus (GBS) as well as attitudes toward vaccination costs and information sources. Results: Overall, 523 respondents were included in this study. The overall awareness of maternal immunization was 16%. Willingness to receive vaccinations during pregnancy was reported for influenza (68%), pertussis (58%), RSV (59%), and GBS (71%). A common reason for vaccine hesitancy included uncertainty about its effects on the fetus. The key factors associated with vaccine acceptance were higher educational attainment and prior knowledge of maternal immunization. Regarding costs, most respondents were willing to pay up to JPY 5000 (approximately USD 35). The most frequently prioritized sources were explanations from physicians, followed by explanations from midwives. Conclusions: Despite low awareness, vaccination intention was comparable to that reported in other countries. Points that may contribute to improved vaccine uptake were also identified. These findings may lead to the prevention of infectious diseases in newborns and infants in Japan and possibly improve public health.

This study aimed to identify the factors predicting rubella vaccination status based on self-reported data and the presence of sufficient rubella antibody titers in pregnant women in Japan. We used the results of the nationwide questionnaire survey conducted at obstetric facilities in the Pregnant Women Health Initiative Project (PWHI), with 23 participating hospitals recruiting pregnant women from June 2018–November 2019. We extracted age, the number of deliveries, educational level, household income, pre-pregnancy smoking, and knowledge of rubella from questionnaires and medical records. We analyzed the association of rubella vaccination status and antibodies with each of these factors. We found that the number of previous deliveries, educational level, annual household income, smoking before pregnancy, and knowledge of rubella were factors predicting self-reported rubella vaccination status, while age and the number of previous deliveries were identified as factors predicting the presence of sufficient rubella antibody titers (32 folds or higher). Women considering pregnancy should be immunized against rubella to prevent congenital rubella syndrome in the future. Furthermore, social policies are needed to strongly encourage vaccination, especially for all citizens who were not given the opportunity or missed the chance to be vaccinated against rubella.

In Japan, rubella antibodies are measured in all pregnant women in order to detect subclinical infection. The study aimed to assess the validity of measuring rubella antibodies to detect subclinical rubella among pregnant women in Japan. This single-center, retrospective study measured rubella hemagglutination inhibition (HI) titers and rubella-specific IgM antibody index values (IgM-values). IgM-values were measured by enzyme immunoassay, and IgM-values > 1.2 were considered positive. Of 14965 pregnant women who were included, 186 (1.2%) were IgM-positive. Only one patient was clinically diagnosed with rubella (HI titer, 1:2048; IgM-value, 10) and developed a fever and skin rash. She decided to terminate her pregnancy without a repeat blood test. Of the IgM-positive patients, 136 (73.1%) had rubella HI titers of < 1:256. The correlation coefficient of rubella HI titers and IgM-values was weakly positive (0.2527; p < 0.0001). This study showed that the single combination of rubella HI and rubella-specific IgM measurements alone did not detect subclinical rubella. Creating awareness among pregnant women by informing them that almost all rubella-specific IgM-positive individuals without symptoms are not acutely infected could decrease their anxiety and prevent unnecessary termination of pregnancies.