Key epidemiological drivers and impact of interventions in the 2020 SARS-CoV-2 epidemic in England

Abstract

A SARS-CoV-2 transmission model fitted to surveillance data estimates virus transmissibility, infection severity, and the impact of interventions. COVID in the community Understanding factors related to the initial spread and control of SARS-CoV-2 is important in light of emerging variants. Knock et al. retrospectively examined differences in SARS-CoV-2 transmission and related mortality in care homes, hospitals, and the community in England since the virus was first introduced in December 2020, stratified by age and geographical region over time. They found that lockdown was by far the most effective control measure and also estimated that mortality in England at this time could have been roughly halved if a lockdown had been introduced 1 week earlier. We fitted a model of SARS-CoV-2 transmission in care homes and the community to regional surveillance data for England. Compared with other approaches, our model provides a synthesis of multiple surveillance data streams into a single coherent modeling framework, allowing transmission and severity to be disentangled from features of the surveillance system. Of the control measures implemented, only national lockdown brought the reproduction number (Rteff) below 1 consistently; if introduced 1 week earlier, it could have reduced deaths in the first wave from an estimated 48,600 to 25,600 [95% credible interval (CrI): 15,900 to 38,400]. The infection fatality ratio decreased from 1.00% (95% CrI: 0.85 to 1.21%) to 0.79% (95% CrI: 0.63 to 0.99%), suggesting improved clinical care. The infection fatality ratio was higher in the elderly residing in care homes (23.3%, 95% CrI: 14.7 to 35.2%) than those residing in the community (7.9%, 95% CrI: 5.9 to 10.3%). On 2 December 2020, England was still far from herd immunity, with regional cumulative infection incidence between 7.6% (95% CrI: 5.4 to 10.2%) and 22.3% (95% CrI: 19.4 to 25.4%) of the population. Therefore, any vaccination campaign will need to achieve high coverage and a high degree of protection in vaccinated individuals to allow nonpharmaceutical interventions to be lifted without a resurgence of transmission.