Assessing herd immunity against rubella in Japan: a retrospective seroepidemiological analysis of age-dependent transmission dynamics

Abstract

ObjectiveWe aimed to epidemiologically assess rubella herd immunity as a function of time, age and gender in Japan, with reference to the recent 2012–2014 rubella epidemic.DesignThis study is a retrospective seroepidemiological analysis.Main outcome measuresThe susceptible fraction of the population was examined as a function of age and time. The age at infection was assessed using reported case data.ResultsWhereas 30 years ago rubella cases were seen only among children, the median (25–75th centiles) age of cases in 2014 was elevated to 32.0 (17.0–42.0) years among males and 27.0 (7.0–37.0) years among females. Susceptible pockets among male birth cohorts 1989–1993 and 1974–1978 were identified, with seropositive proportions of 70.0% and 68.0%, respectively. The majority of female age groups had greater seropositive proportions than the herd immunity threshold, with a minor susceptible pocket for those born from 1989 to 1993 (78.3% seropositive). The age-standardised seronegative proportion decreased to 18.3% (95% CI 16.8% to 19.8%) among males and 15.6% (95% CI 10.0% to 21.2%) among females in 2013, and the immune fraction was not sufficiently below the herd immunity threshold. While the number of live births born to susceptible mothers in 1983 was estimated at 171 876 across Japan, in 2013 it was reduced to 23 698.ConclusionsAn elevated age at rubella virus infection and the presence of susceptible pockets among adults were observed in Japan. Although, overall, the absolute number of rubella cases has steadily declined in Japan, the elevated age of rubella cases, along with increased numbers of susceptible adults, contributed to the observation of as many as 45 congenital rubella syndrome (CRS) cases, which calls for supplementary vaccination among susceptible adults. Assessing herd immunity is considered essential for routinely monitoring the risk of future rubella epidemics and CRS cases.

Reconstructing the transmission dynamics of rubella in Japan, 2012-2013

“…Japan experienced a nationwide rubella epidemic from 2012 to 2013, which involved many infections among adults with a total of 45 reported CRS cases. While the country has clearly been on its way to achieve sufficient herd immunity to prevent any additional major epidemics, a seroepidemiological analysis of rubella revealed a “pocket” of susceptible individuals among males aged 30–49 years [ 2 ].…”

“…The metapopulation epidemic model is a suitable tool to capture spatiotemporal dynamics over discrete patches, which are in line with the actual spatial distribution of a total of 47 prefectures in Japan [ 9 ]. Given that a substantial fraction of adults remains susceptible in the present day population in Japan [ 2 ], it is essential to explore possible vaccination strategies. The present study aimed to capture the spatiotemporal patterns of rubella using a parsimonious metapopulation epidemic model and examine the potential usefulness of a vaccination program that focuses on spatial heterogeneity.…”

History repeats itself in Japan: Failure to learn from rubella epidemic leads to failure to provide the HPV vaccine

“…Sadly, the history of vaccine crisis repeats itself in Japan. According to the previous studies, 3,6 the presence of disease-susceptible pockets was observed among the Japanese population, as shown in Fig. 1 .…”

“…As a result, there are susceptible pockets among female birth cohorts 1989–1993, with seropositive proportions of 78.3%. 3 …”

Rubella seroprevalence using residual samples from the South African measles surveillance program: a cross-sectional analytic study

“…[9][10][11] and in other WHO regions. [12][13][14] When planning RCV introduction, serosurveys provide insight into the population subgroups that should be targeted for vaccination and provide data for modeling rubella transmission dynamics [15][16][17] including estimation of the burden of congenital rubella syndrome (CRS). Individuals of reproductive age are of particular interest since susceptibility to rubella in this age group has a direct impact on occurrence of CRS, which is the main target of the RCV.…”