Improving vaccination coverage and offering vaccine to all school-age children will allow uninterrupted in-person schooling in King County, WA: Modeling analysis
Authors: Bracis Chloe , Moore Mia , Swan David A. , Matrajt Laura , Anderson Larissa , Reeves Daniel B. , Burns Eileen , Schiffer Joshua T. , Dimitrov Dobromir 
Published: October 2021

Background

The mass rollout of COVID vaccination in early 2021 allowed local and state authorities to relax mobility and social interaction regulations in spring 2021 including lifting all restrictions for vaccinated people and restoring in-person schooling. However, the emergence and rapid spread of highly transmissible variants combined with slowing down the pace of vaccination created uncertainty around the future trajectory of the epidemic. In this study we analyze the expected benefits of offering vaccination to children age 5-11 under differing conditions for in-person schooling.

Methods

We adapted a mathematical model of SARS-CoV-2 transmission, calibrated to data from King County, Washington, to handle multiple variants with increased transmissibility and virulence as well as differential vaccine efficacies against each variant. Reactive social distancing is implemented driven by fluctuations in the number of hospitalizations in the county. We simulate scenarios offering vaccination to children aged 5-11 with different starting dates and different proportions of physical interactions (PPI) in schools being restored. The impact of improving overall vaccination coverage among the eligible population is also explored. Cumulative hospitalizations, percentage reduction of hospitalizations and proportion of time at maximum social distancing over the 2021-2022 school year are reported.

Findings

In the base-case scenario with 85% vaccination coverage of 12+ year-olds, our model projects 4945 (median, IQR 4622-5341) total COVID-19 hospitalizations and 325 (median, IQR 264-400) pediatric hospitalizations if physical contacts at schools are fully restored (100% PPI) for the entire school year compared to 3675 (median, IQR 2311-4725) and 163 (median, IQR 95-226) if schools remained closed. Reducing contacts in schools to 75% PPI or 50% PPI through masking, ventilation and distancing is expected to decrease the overall cumulative hospitalizations by 2% and 4% respectively and youth hospitalizations by 8% and 23% respectively. Offering early vaccination to children aged 5-11 with 75% PPI is expected to prevent 756 (median, IQR 301-1434) hospitalizations and cut hospitalizations in the youngest age group in half compared to no vaccination. It will largely reduce the need of additional social distancing over the school year. If, in addition, 90% overall vaccination coverage is reached, 60% of remaining hospitalizations will be averted and the need of extra mitigation measures almost certainly avoided.

Conclusions

Our work highlights that in-person schooling is possible if reasonable precaution measures are taken at schools to reduced infectious contacts. Rapid vaccination of all school-aged children will provide meaningful reduction of the COVID health burden over this school year but only if implemented early. Finally, it remains critical to vaccinate as many people as possible to limit the morbidity and mortality associated with the current surge in Delta variant cases.