In this part, I will talk about school closures, a non-pharmaceutical intervention at the community level. After completing this part, you should be able to explain why school-age children are important in transmission of some infectious diseases, to describe the potential impact of school closures, and to discuss the practical difficulties associated with closing schools. It is well known that school-age children are of primary importance in the transmission of many respiratory infections in the community. A survey of social contact patterns, in eight European countries, identified children as the group with the greatest frequency of contacts. The heat plot, shown here, indicates the frequency of social contacts, with highest frequency shown in white. We can clearly see the frequency of contacts between children is high. The diagonal band indicates that contacts tend to be most frequent among people of similar ages, and the two off-diagonal bands show the contacts between children and their parents. The investigators considered what would happen if a new pathogen emerged in a completely susceptible population and was spread through close contacts as, for example, a respiratory virus might be. Based on these patterns, the investigators determined that incidence of infections with the new pathogen would be highest in children. Influenza virus spreads through close contact, and rates of infections in children tend to be higher than in other age groups in influenza epidemics and pandemics. That is not to say that children have the greatest burden of severe disease, because influenza virus infections are often milder in children than in adults and the elderly. Because of the high rate of infections in children, and particularly in schools, the closure of schools during epidemics is a non-pharmaceutical intervention with particular promise. Going back a hundred years, the 1918 influenza pandemic had a devastating impact on the world. School closure was a common intervention used in many locations to try to slow transmission, and there is some evidence that early implementation of school closures was effective. School closures were also used in other pandemics and epidemics. In the 21st Century, here where I am in Hong Kong, authorities closed schools for three weeks during the peak of the SARS epidemic in 2003, and, more recently, schools were closed to control influenza epidemics in 2008 and in 2009. In March 2008, at the height of the winter influenza season, and following three pediatric deaths associated with influenza, the government announced that it would close all nurseries, kindergartens, and primary schools the following day, for a week. This would then be followed, immediately, by the scheduled one week Easter break, for a total closure period of two consecutive weeks. We can look at what happened, and try to make some inferences about the impact of school closure. Here we can see the weekly consultation rate of influenza-like illnesses in Hong Kong, and the weekly detection rates of influenza viruses in children and adults. Infections peaked in mid to late February, and incidence rates were declining by the school closure period that started on the 13th of March. Rather than try to directly interpret changes in the epidemic curves, we used a statistical approach to estimate the daily reproductive number. Shown here, the reproductive number dipped below one just before the peak in incidence, and was declining throughout early March, or there was a decline in transmission during and after the closure period, this most likely reflects the waning in the epidemic that would have occurred regardless of the school closures. Since the emergence of avian influenza A (H5N1), the past 10 years have seen intensive preparations for the next influenza pandemic. In the early years of the 21st Century, many plans were based on the potential for another pandemic like 1918, stimulated by the severity of human infections with H5N1. Many local and national administrations included school closures in their plans for the response to a new influenza pandemic, as part of a broader range of measures that could be implemented depending on the local situation and the estimated severity of the new pandemic virus. Those pandemic plans were put to the test in 2009 when swine flu emerged, first in North America, and rapidly spread around the world. Within days of the announcement of the identification of the new H1N1 strain of swine flu, and its potential to cause a pandemic, the administration in Hong Kong announced their plans for responding. Part of the response would include school closures for at least two weeks, once the first non-imported case was identified, indicating that transmission was occurring in the local community. What actually happened is that despite imported cases being identified throughout May and early June, the first non-imported case was not identified until June the 9th and, on June the 10th, the announcement was made that nurseries, kindergartens, and primary schools would all close for two weeks. Secondary schools were only closed if swine flu cases were identified in that school. Subsequently, the school closures were extended to the start of summer vacation in mid July, and lasted for around a month in total. We examined the impact of the school closures on the course of the first wave of pandemic H1N1 in Hong Kong. We constructed a transmission model with three age classes: children less than 12 years of age, children 13 to 17 years of age, and adults 18 years of age or older. In the absence of local data on social contacts, we used the European data to parameterize the relative transmissibility within and between age groups, and we allowed susceptibility to vary by age. We then estimated the changes in the proportion of infections that were notified over time, called the reporting rate, and the change in transmissibility associated with the school closures in younger children and the school vacation in all children. Here are our results. We estimated that transmission within children dropped 70% during the school closures and summer vacation, with a reproductive number of 1.7 before June the 11th, 1.5 between June the 12th and July the 10th, and 1.1 after July the 10th. As part of the model, we estimated that reporting rates began to decline in mid-June and stopped declining on June the 29th, with a final reporting rate of 5.2%. This is very consistent with a separate serological study, in which we estimated that 3.9% of infections were laboratory confirmed. We also estimated that children were 2.6 times as susceptible to infection as adults, consistent with a separate study, in the United States, in which children were twice as susceptible to infection. In conclusion, we demonstrated that school closures reduced overall transmission by 25 percent, and delayed the peak in H1N1 incidence to September, when schools re-opened. Other studies have demonstrated significant impact of school closures in the 2009 pandemic, while simulation studies have shown how this type of intervention can flatten the peak of an epidemic, reducing both the peak attack rate, which can help to prevent hospitals from being overwhelmed, and also reducing the cumulative incidence of infections. Having presented the benefits of school closures, I will finish with a few comments on the limitations of this intervention. In many locations in which it is common for both parents to work, school closures can cause major disruption and economic loss to families because of the need to arrange child care at short notice. In addition, many children in deprived areas are reliant on subsidized school meals. School closures are therefore likely to be considered only in the most serious situations, such as severe influenza pandemics.
