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Background: Measles outbreaks are still routine, even in countries where vaccination coverage exceeds the guideline of 95%. Therefore, achieving ambitions for measles eradication will require understanding of how unvaccinated children interact with others who are unvaccinated. It is well established that schools and homes are key settings for both clustering of unvaccinated children and for transmission of infection. In this study, we evaluate the potential for contacts between unvaccinated children in these contexts to facilitate measles outbreaks with a focus on the Netherlands, where large outbreaks have been observed periodically since the introduction of mumps, measles and rubella (MMR). Methods and findings: We created a network of all primary and secondary schools in the Netherlands based on the total number of household pairs between each school. A household pair are siblings from the same household who attend a different school. We parameterised the network with individual level administrative school and household data provided by the Dutch Ministry for Education and estimates of school level uptake of the MMR vaccine. We analysed the network to establish the relative strength of contact between schools and found that schools associated with low vaccine uptake are highly connected, aided by a differentiated school system in the Netherlands (Coleman homophily index (CHI) = 0.63). We simulated measles outbreaks on the network and evaluated the model against empirical measles data per postcode area from a large outbreak in 2013 (2,766 cases). We found that the network-based model could reproduce the observed size and spatial distribution of the historic outbreak much more clearly than the alternative models, with a case weighted receiver operating characteristic (ROC) sensitivity of 0.94, compared to 0.17 and 0.26 for models that do not account for specific network structure or school-level vaccine uptake, respectively. The key limitation of our framework is that it neglects transmission routes outside of school and household contexts. Conclusions: Our framework indicates that clustering of unvaccinated children in primary schools connected by unvaccinated children in related secondary schools lead to large, connected clusters of unvaccinated children. Using our approach, we could explain historical outbreaks on a spatial level. Our framework could be further developed to aid future outbreak response. Using Dutch household networks, James Munday and team investigate the risk of measles spreading in populations with high MMR uptake. Author summary: Why was this study done? ○ The measles, mumps and rubella (MMR) vaccine is very effective at protecting against measles infection; however, outbreaks are still possible especially when larger numbers of unvaccinated people group together allowing longer transmission chains to form. ○ In the Netherlands, 2 groups in particular are associated with low vaccine uptake, and these groups are associated with particular schools in the differentiated school system, creating clusters of unvaccinated children in these schools. ○ We wanted to understand if these schools are also well connected to each other through relationships in shared households (e.g., siblings that attend 2 separate schools) and what this means for outbreak risk in the Netherlands. What did the researchers do and find? ○ We constructed a network of all the schools in the Netherlands and quantified how connected each pair of schools is by counting the number of children in one school that share a household with a child in the other school. ○ We used this data to assess how connected the schools that were associated with low vaccine uptake were to each other and constructed a model of disease transmission between schools to assess the implications of this connectivity. ○ We found that these schools were more connected to each other than would be expected based on the patterns of connectivity in the rest of the network (Coleman homophily index (CHI) of 0.63) and that this additional connectedness was important in explaining the nature of a past measles epidemic. What do these findings mean? ○ Our findings highlight the role of the structure of the differentiated school system in allowing large outbreaks to occur and offer an explanation for why outbreaks in the Netherlands tend to be so large compared to other countries with similar vaccine uptake. ○ The framework we use can be adapted to evaluate ongoing risk of measles outbreaks by re-parameterising with updated school-connectivity and renewed estimates of susceptibility in each school by combining historical outbreak and vaccine uptake data. ○ The main limitation of our approach is that it only considers schools and household contexts and does not account for infectious transmission outside of these settings. [ABSTRACT FROM AUTHOR]

The spread of viral respiratory infections is intricately linked to human interactions, and this relationship can be characterized and modelled using social contact data. However, many analyses tend to overlook the recurrent nature of these contacts. To bridge this gap, we undertake the task of describing individuals' contact patterns over time by characterizing the interactions made with distinct individuals during a week. Moreover, we gauge the implications of this temporal reconstruction on disease transmission by juxtaposing it with the assumption of random mixing over time. This involves the development of an age-structured individual-based model, using social contact data from a pre-pandemic scenario (the POLYMOD study) and a pandemic setting (the Belgian CoMix study), respectively. We found that accounting for the frequency of contacts impacts the number of new, distinct, contacts, revealing a lower total count than a naive approach, where contact repetition is neglected. As a consequence, failing to account for the repetition of contacts can result in an underestimation of the transmission probability given a contact, potentially leading to inaccurate conclusions when using mathematical models for disease control. We, therefore, underscore the necessity of acknowledging contact repetition when formulating effective public health strategies. [ABSTRACT FROM AUTHOR]

Background In the Netherlands, the number of mpox cases started declining before mpox vaccination was initiated. Most cases were men who have sex with men (MSM). We investigated whether the decline in mpox could be attributed to infection-induced immunity or behavioral adaptations. Methods We developed a transmission model and accounted for possible behavioral adaptations: fewer casual partners and shorter time until MSM with mpox refrain from sexual contacts. Results Without behavioral adaptations, the peak in modelled cases matched observations, but the decline was less steep than observed. With behavioral adaptations in the model, we found a decline of 16%–18% in numbers of casual partners in June and 13%–22% in July 2022. Model results showed a halving of the time before refraining from sex. When mpox vaccination started, 57% of MSM with very high sexual activity in the model had been infected. Model scenarios revealed that the outbreak could have waned by November 2022 even without vaccination. Conclusions The limited duration of the mpox outbreak in the Netherlands can be ascribed primarily to infection-induced immunity among MSM with high sexual activity levels. The decline was accelerated by behavioral adaptations. Immunity among those most sexually active is essential to impede mpox resurgence. [ABSTRACT FROM AUTHOR]

Mpox has spread rapidly to many countries in nonendemic regions. After reviewing detailed exposure histories of 109 pairs of mpox cases in the Netherlands, we identified 34 pairs where transmission was likely and the infectee reported a single potential infector with a mean serial interval of 10.1 days (95% credible interval, 6.6–14.7 days). Further investigation into pairs from 1 regional public health service revealed that presymptomatic transmission may have occurred in 5 of 18 pairs. These findings emphasize that precaution remains key, regardless of the presence of recognizable symptoms of mpox. [ABSTRACT FROM AUTHOR]