Varicella outbreak at nursery school under routine immunization in Japan in 2017 and 2018 and vaccine effectiveness.

BACKGROUND: In Japan, routine administration to one-year-old children of two-dose immunization for varicella was introduced in October 2014. Object The object of this study was to report outbreaks of varicella under routine immunization at a nursery school and in its surrounding area using data of surrounding areas from the (Nursery) School Absenteeism Surveillance System. Then, we measured the effectiveness of routine two-dose immunization for varicella to onset. We tentatively assessed its severity in a nursery school. METHOD: The study period extended from April 2017 through March 2018. The study area comprised Nursery school B and other nursery schools, and elementary and junior high schools in City A. Subjects in Nursery school B were 120 children. We analyzed vaccine effectiveness (VE) as an observational study and assessed severity using Fisher's exact test. We also assessed VE for severity using linear regression. Severity was defined as the length of nursery school absence attributable to varicella infection. RESULTS: During the one month preceding a period of two weeks before the initial case at Nursery school B, there were 16 cases of varicella infection in nursery schools, 45 cases in elementary schools, and one case in junior high schools in City A. For children who had received one vaccine dose or more, VE was 48.1% for all ages and 49.2% among children three years old and older. No significant VE against infection was found. Vaccination using one dose or more can reduce severity significantly. DISCUSSION AND CONCLUSION: Because many nursery school children who had received two doses of vaccine were infected, VE was estimated as low in the nursery school and not significant. Although VE for severity with more than one dose was confirmed, a second dose might not reduce severity compared to one dose.

Susceptibility of nursery teachers to measles, rubella, varicella and mumps in Japan.

BACKGROUND: A guideline published in 2018 by the Ministry of Health, Labour and Welfare stipulated confirmation of the vaccine history of nursery staff members. OBJECT: This study was conducted to elucidate nursery teachers' vaccine and infection histories for measles, mumps, rubella, and varicella through survey responses. METHOD: After sending questionnaires through the mail to 5000 nursery teachers in November 2022, we received responses through December 2022. We measured the proportion of susceptibility in three ways. Additionally, we compared the proportions of susceptibility by disease by age class. RESULTS: After receiving 1620 responses in all, the data of 1229 respondents under 50 years old were analyzed. Under the broad definition by which "no answer" was also regarded as unvaccinated or uinfected as well as "unknown," the proportions of susceptibility for measles, rubella, and varicella were higher: 22-23%. For mumps, the proportion was 42%. For varicella, they were 31% for respondents in their 30 s, and 14% for respondents in their 40 s. For mumps, the respective values were 58% and 26%. DISCUSSION: Respondents assessed for this study were less susceptible and unknown in comparison with earlier studies investigating health care workers, school teachers, university students, and pregnant women. CONCLUSION: The survey revealed that measles and rubella susceptibility was higher among respondents in their 30 s. However, it was higher for varicella and mumps among respondents in their 20 s.

Nursery school absenteeism surveillance system and infection control measures in nursery schools.

INTRODUCTION: The Nursery School Absenteeism Surveillance System (NSASSy), which includes 40% of all nursery schools in Japan, has a degree of effectiveness that is difficult to prove: nursery schools and areas without NSASSy cannot be evaluated for their incidence of infectious diseases as precisely as those with NSASSy. Instead, we examine nursery school countermeasures against infectious diseases by considering the endogeneity bias of NSASSy. METHOD: After sending questionnaires to 500 Tokyo metropolitan and nearby nursery schools in November 2022, we received their responses through the end of 2022. Questionnaires asked about infection control measures of nursery schools: (1) cooperation with public health centers; (2) cooperation with staff; (3) cooperation with children's parents; (4) precautions among children; (5) countermeasure systems; (6) precaution systems; (7) recording of health conditions of children; (8) usefulness of studying while students; and (9) usefulness of training at nursery schools. Ordered probit with inverse probability weighted adjustment was used as the estimation procedure. The explanatory variable was a dummy variable for using NSASSy. Probability in weight was estimated using the first-step probit for NSASSy. Explanatory variables were a dummy variable for publicly funded nursery schools and a dummy variable for local governments that had adopted NSASSy. RESULTS: We analyzed 193 nursery schools. NSASSy was negative and associated significantly with (3) cooperation with children's parents and (7) recording of health conditions of children. These countermeasures were more likely to have been taken by NSASSy nursery schools.