This study revealed that, as of late 2020, there is currently insufficient voluntary action being taken by high-risk adults in the Japanese general population (excluding healthcare-related workers) to confirm their rubella immune status: only 23.4% of men and 39.4% of women in their 20s to 40s have taken some action related to rubella prevention. Thus, our findings indicate that there is still some way to go in achieving rubella elimination in Japan.
The first of the three major factors we found to be associated with the targeted population having taken voluntary action to check their rubella immune status was having knowledge about testing for confirmation of immunity status, about the rubella outbreak in 2013 among men in their 20s to 40s, and about CRS. It has been reported that knowledge about vaccine-preventable disease is closely associated with uptake of the influenza [15, 16], measles-rubella containing [22, 23], hepatitis A , and pertussis  vaccines. In the present study, knowledge that testing can confirm immune status showed a strong association with taking voluntary action among both men and women (men: AOR 4.29, 95%CI 6.06-11.93; women AOR 2.89, 95% CI 2.00-4.18). This suggests that Japan’s test and vaccination strategy has successfully prompted some of those reached by the promotion to actually take action. Further evidence that Japan’s current strategies are working are our findings that working-age men have become more aware of their role in CRS following the 2013 outbreak. An effective intervention to reach more of the 20- to 40-year-old target population could involve providing further information in the workplace about rubella the need to check immune status, and how to check it, via posters, pamphlets, or possibly occupational health activities inside larger companies.
The second factor that we found to be associated with taking voluntary action was having acquaintances who were vaccinated against or tested for rubella, and this association was found for both men and women. This is in agreement with the results of previous online surveys about rubella in Japan that reported the association for vaccination  and testing  of an acquaintance. Learning that a close acquaintance has been vaccinated or tested may instill a sense of security and highlight the benefits of taking action, which may be an effective strategy in collectivist societies like Japan . Given that promotion activities through social networking sites such as Twitter and Facebook [27, 28] and through commercial and social marketing have been shown to be effective for vaccine uptake, activities involving familiar people might also be an effective strategy. Moreover, potential interventions could, for example, involve interested employees voluntarily sharing their experiences of vaccination during promotional activities run by occupational health personnel or encouraging people to share their experiences of testing or vaccination with friends through social networking service (SNS).
Lastly, among both men and women, getting vaccinated every year against influenza was associated with taking voluntary action to confirm rubella immunity, compared with never having been vaccinated against influenza. These findings are in agreement with other studies that have reported the association of annual influenza vaccination behavior with vaccine uptake [15, 16, 18]. People who have influenza vaccinations every year are likely to worry less about the side effects of the vaccine, be keenly interested in medical care, and have easy access to it. Therefore, it is important that promotions are targeted to reach people who are not interested or do not have easy access to medical care. A possible workplace-related intervention could be to include measurement and explanation of rubella antibody titer at the annual medical check-ups offered by companies in compliance with the labor law. This strategy could reach working-age company employees who are not interested in seeking out medical information, enabling them to easily confirm their immune status.
The life course events of marriage, desire for pregnancy, and having children were associated with taking voluntary action to confirm rubella status, albeit weakly in this study. Getting married tended to be associated with such action among men in the univariate analysis (OR 2.79, 95% CI 2.04-3.80) but not after multivariate adjustment (AOR 1.03, 95% CI 0.56-1.91), and men tended not to be interested in rubella before getting married but were more interested after getting married (AOR 1.03, 95% CI 0.56-1.91). An online study of the general adult population in 2014 also reported voluntary action was strongly associated with getting married . We found that desire for pregnancy and having children showed weak associations with taking action, although the previous 2014 study found a strong association with desire to get married . Also, a recent study conducted in 2020 with Japanese men aged 41-47 years found no association between partner’s current desire for pregnancy and undergoing rubella antibody testing (AOR 0.98, 95% CI 0.87-1.11) . Because all pregnant woman are routinely tested for rubella antibody as part of antenatal care in Japan, experience of pregnancy is a confounder in women and is one of the reasons for the higher OR seen for women with children. Overall, our findings indicate that the switch from measures centered on pregnant women and their partners to measures centered on men in 2019 is having a positive impact, which is encouraging, but we need to reach more men to encourage them to take voluntary action to confirm their rubella immune status.
Surprisingly, we found that women in their 40s were significantly less likely to have taken voluntary action to confirm rubella immune status than those in their 20s. Current promotion activities mainly target pregnant women and men in their 40s, and the free testing and vaccination policy does not cover women without desire for pregnancy. Interest in rubella prevention has clearly fallen among women in their 40s. In addition, a recent report from the National Institute of Infectious Diseases indicates that seroprevalence is decreased among those aged 55-69 . It is therefore necessary to design a system that allows all generations to confirm their own immunity with no one left behind.
We did not find an association between highest education level and taking action to confirm rubella immune status. There have been studies that have found an association between education level and vaccine intake—in the Bahamas , Lebanon , and United States —and those that have found no such association—in Canada  and Japan . The high literacy rate, easy access to written information, and high education level among all generations in Japan suggests that promotion activities can make good use of written information.
It seems that more men and women in their 20s to 40s have taken action as of late 2020 compared with 2013, when around 25% of women and men with desire for pregnancy but just 7.3% of women and 2.9% of men without a current desire for pregnancy had been tested for rubella antibody or vaccinated against rubella . Even though our findings in late 2020 indicate that still only 39.4% of women and just 23.4% of men had taken some action to confirm their immunity, these are more encouraging rates, especially among women. Therefore, it seems then that the government’s testing and vaccination strategy that started targeting those with desire for pregnancy and their family members in 2019 is working to some extent  to close this identified immunity gap. This would also explain the gap in taking action between women and men in our study. It is important to note, however, that a recent survey in Japan reported that only 21.3% of men had actually been tested for rubella antibody . So, while our study indicates that the government’s promotion activities have been reaching the targeted populations, there are still insufficient numbers of people taking the necessary preventive action to eliminate rubella in the very short term (originally 2020). Further strategies involving, for example, the annual medical check-ups, collaborations in occupational health activities, and encouragement to share experiences with friends through SNS are needed to promote action among those at high risk of rubella infection as well as hard-to-reach and left-behind populations.
Our study had some limitations. First, because data were obtained from a randomly selected online survey population, our findings cannot be considered representative of the general Japanese population as a whole. Second, self-report bias and selection bias may have resulted in overestimation of the results, although given that the targeted age group in their 20s to 40s tends to be familiar with information technology and to have internet access, we believe this did not adversely affect our primary objective of identifying factors associated with their participation in the SIAs. Third, this was a cross-sectional study, so we cannot infer causal relationships. Lastly, we did not consider the potential influence of the relationship between the rubella outbreaks and variation in efficacy of the live rubella vaccine across years. However, Japan does have strict quality control standards in place for vaccines . Despite these limitations in study design, we believe that our up-to-date survey results are important to policy makers in deciding how to further accelerate measures for the elimination of rubella in Japan.