Substantial Impact of School Closure on the Transmission Dynamics during the Pandemic Flu H1N1-2009 in Oita, Japan

Abstract

Background: School closure is considered as an effective measure to prevent pandemic influenza. Although Japan has implemented many class, grade, and whole school closures during the early stage of the pandemic 2009, the effectiveness of such a school closure has not been analysed appropriately. In addition, analysis based on evidence or data from a large population has yet to be performed. We evaluated the preventive effect of school closure against the pandemic (H1N1) 2009 and examined efficient strategies of reactive school closure.

Materials and methods: Data included daily reports of reactive school closures and the number of infected students in the pandemic in Oita City, Japan. We used a regression model that incorporated a time delay to analyse the daily data of school closure based on a time continuous susceptible-exposed-infected-removed model of infectious disease spread. The delay was due to the time-lag from transmission to case reporting. We simulated the number of students infected daily with and without school closure and evaluated the effectiveness.

Results: The model with a 3-day delay from transmission to reporting yielded the best fit using R2 (the coefficient of determination). This result suggests that the recommended period of school closure is more than 4 days. Moreover, the effect of school closure in the simulation of school closure showed the following: the number of infected students decreased by about 24% at its peak, and the number of cumulative infected students decreased by about 8.0%.

Conclusions: School closure was an effective intervention for mitigating the spread of influenza and should be implemented for more than 4 days. School closure has a remarkable impact on decreasing the number of infected students at the peak, but it does not substantially decrease the total number of infected students.

Fig 1. Structure of the transmission model that incorporates a time delay.

Diagram of the relationship between the day of infection, the day of becoming infectious, and the day a case is reported, in the case of d = 3. The symbol of a virus indicates transmission. $\widehat{S}$ and $\widehat{I}$ are observed values of daily reports. S and I are theoretical values. I ₄(t + 1) is derived from S(t − 3), infected by I ₃(t − 3), becomes infectious at t, and is reported as a case at (t + 1). I ₁ and I ₂ indicate exposed students (i.e., I ₁ = E ₁ and I ₂ = E ₂). I ₄ is not infectious because it is absent from school.

Fig 2. Time course of pandemic (H1N1) 2009 in Oita City, Japan.

From September 2009 to March 2010, (A) a comparison of infected raw values of students and the moving average for 7-day values, (B) comparison of the number of absent students under school closure and students reported as a case, and (C) comparison of absolute humidity (AH) and the number of students reported as a case. The grey dashed line indicates AH of 11 g/m³. The number of absent students under school closure, number of students reported as a case, and AH are shown as a moving average for 7 days.

Fig 3. Sentinel reports by age group in Oita City, Japan from September 2009 to March 2010.

Data were collected from 16 randomly chosen hospitals in Oita City and provided by Oita City Health Care Centre. The general age distribution in Japanese schools is 4–6 years for kindergarten, 7–12 years for elementary school, 13–15 years for junior high school, and 16–18 years for high school students.

Fig 4. Simulated time course with various degrees of delay d = 1–5 in Oita City, Japan.

From September 2009 to March 2010, (A) the number of newly infected students and (B) cumulative number of infected students. The parameters we used for each d are shown in Table 1.

Fig 5. Simulated time course with and without school closure in d = 3 in Oita City, Japan.

From September 2009 to March 2010, (A) the number of newly infected students and (B) cumulative number of infected students.