A seroepidemiological study across age groups before and after the 2010-2011 mumps epidemic in Japan

In Japan, large-scale mumps epidemics recur every 4-6 years because of low vaccination coverage. This study aimed to describe the seroprevalence of mumps in the Japanese population and identify the age groups most affected. The prevalence of anti-mumps antibodies was evaluated based on 1000 serum samples obtained from the Japanese National Serum Reference Bank. These samples consisted of 50 sera for each of 10 different age groups, collected during 2007-2008 (pre-epidemic period) and 2012-2013 (post-epidemic period). Seropositivity was lowest in the 6-11 months subgroup (3% and 0% in pre- and post-epidemic periods, respectively) and highest in the 10-14 years group (66% and 72% in pre- and post-epidemic periods, respectively). A comparison of anti-mumps antibody prevalence throughout the two periods considered revealed a large rise in seropositivity among the 2004-2008 birth cohort, using that of the 1-4 years group as representative in the pre-epidemic period (from 22% in pre- to 58% in post-epidemic periods; p = 0.0002). These results indicate that most people likely gain antibodies to the mumps virus during their childhood, especially during the first epidemic that they experience after their second year of life. Therefore, children should be vaccinated against mumps soon after their first birthday for effective prevention.

The optimal age of vaccination against dengue in Brazil based on serotype-specific forces of infection derived from serological data

In this paper, we study a single serotype transmission model of dengue to determine the optimal vaccination age for Dengvaxia. The transmission dynamics are modelled with an age-dependent force of infection. The force of infection for each serotype is derived from the serological profile of dengue in Brazil without serotype distinction and from serotype-specific reported cases. The risk due to an infection is measured by the probability of requiring hospitalization based on Brazilian Ministry of Health data. The optimal vaccination age is determined for any number and combination of the four distinct dengue virus serotypes DENv1-4. The lifetime expected risk is adapted to include antibody dependent enhancement (ADE) and permanent cross-immunity after two heterologous infections. The risk is assumed to be serostatus-dependent. The optimal vaccination age is computed for constant, serostatus-specific vaccine efficacies. Additionally, the vaccination age is restricted to conform to the licence of Dengvaxia in Brazil and the achievable and minimal lifetime expected risks are compared. The optimal vaccination age obtained for the risk of hospitalization varies significantly with the assumptions relating to ADE and cross-immunity. Risk-free primary infections lead to higher optimal vaccination ages, as do asymptomatic third and fourth infections. Sometimes vaccination is not recommended at all, e.g. for any endemic area with a single serotype if primary infections are risk-free. Restricting the vaccination age to Dengvaxia licensed ages mostly leads to only a slightly higher lifetime expected risk and the vaccine should be administered as close as possible to the optimal vaccination age.