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. 2025 Jul 3;20(7):e0327719.
doi: 10.1371/journal.pone.0327719. eCollection 2025.

The effect of policy measures, school holidays and travel on the incidence of SARS-CoV-2 infection in children and adults in Estonia from 2021 to 2022

Affiliations

The effect of policy measures, school holidays and travel on the incidence of SARS-CoV-2 infection in children and adults in Estonia from 2021 to 2022

Hiie Soeorg et al. PLoS One. .

Abstract

Purpose: The policy measures implemented during the COVID-19 pandemic, travel and school holidays could have influenced the spread of SARS-CoV-2 infection in children and adults differently. We aimed to determine the effect of policy measures, school holidays and travel on the incidence of SARS-CoV-2 infection in children and adults.

Methods: The overall SARS-CoV-2 infection incidence between 1 February 2021 and 1 May 2022 was decomposed into the most common lineage-specific incidence per 100,000 by imputing lineage based on the sequencing results of random samples. A phenomenological logistic growth model was fitted to the incidence data in adults (aged ≥15 years) and children (aged <15 years) in four regions in Estonia. Factors influencing the spread of the virus, such as policy measures, school holidays, the number of travel-related cases, and cumulative vaccination or infection rates, were tested as covariates in the model.

Results: The eleven most common lineages (one Alpha, six Delta, two Omicron BA.1, and two Omicron BA.2) caused 84.7% and 85.8% of all SARS-CoV-2 infections in children and adults, respectively, during the study period. According to the final model, the Delta variant had slower growth and a lower maximum cumulative incidence. The number of workplace closures in the previous week and school holidays in the same week decreased, but the number of travel-related cases in the same week increased the incidence growth. No difference between children and adults was observed. The testing rate was lower during school holidays than during school terms (median (IQR) 1964 (1437-2970) vs. 3136 (2476-4417) vs. per 100,000; p < 0.001). In 40.3% of the weeks, travel-related cases were detected, accounting for (IQR) 2.1% (0.9-4.3%) of the incidence of nontravel-related infections.

Conclusion: Our study suggests that the spread of SARS-CoV-2 infection was similar in children and adults. Workplace closures reduced transmission, whereas during school holidays lower testing contributed to a lower reported incidence, and travel-related cases were possibly underreported.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Weekly incidence per 100,000 of SARS-CoV-2 infections in adults (≥15 years) and children (<15 years).
The incidence is decomposed into lineage-specific incidences of the eleven most common lineages and other lineages.
Fig 2
Fig 2. Individual predictions from the final model.
The observed incidences of the most common lineages in the four regions and adults (red) and children (grey) and model-predicted incidences over the time of spread are shown. Solid lines represent individual predictions, and the shaded area around them bounded by dashed lines represents the 95% prediction interval. The grey shaded areas represent the timing of school holidays.
Fig 3
Fig 3. Simulations of cumulative incidence rates.
Simulated total number of infections compared with the actual total number of infections (A) if workplace closure had been at least at the level required for some or all-but-essential sectors and (B) if no travel-related cases or twice as many travel-related cases had occurred.

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References

    1. Koslow W, Kühn MJ, Binder S, Klitz M, Abele D, Basermann A, et al. Appropriate relaxation of non-pharmaceutical interventions minimizes the risk of a resurgence in SARS-CoV-2 infections in spite of the Delta variant. PLoS Comput Biol. 2022;18(5):e1010054. doi: 10.1371/journal.pcbi.1010054 - DOI - PMC - PubMed
    1. Dings C, Selzer D, Bragazzi NL, Möhler E, Wenning M, Gehrke T, et al. Effect of vaccinations and school restrictions on the spread of COVID-19 in different age groups in Germany. Infect Dis Model. 2024;9(4):1250–64. doi: 10.1016/j.idm.2024.07.004 - DOI - PMC - PubMed
    1. Puia A, Pop SR, Manzat BOC, Pintea S, Puia IC, Fadgyas-Stanculete M. Coping Strategies Among Healthcare Workers During the COVID-19 Pandemic: Emotional Responses, Challenges, and Adaptive Practices. Medicina (Kaunas). 2025;61(2):311. doi: 10.3390/medicina61020311 - DOI - PMC - PubMed
    1. Nguyen MH, Nguyen THT, Molenberghs G, Abrams S, Hens N, Faes C. The impact of national and international travel on spatio-temporal transmission of SARS-CoV-2 in Belgium in 2021. BMC Infect Dis. 2023;23(1):428. doi: 10.1186/s12879-023-08368-9 - DOI - PMC - PubMed
    1. Aiewsakun P, Jamsai B, Phumiphanjarphak W, Sawaengdee W, Palittapongarnpim P, Mahasirimongkol S. Spatiotemporal evolution of SARS-CoV-2 in the Bangkok metropolitan region, Thailand, 2020-2022: implications for future outbreak preparedness. Microb Genom. 2023;9(12):001170. doi: 10.1099/mgen.0.001170 - DOI - PMC - PubMed