Abstract
The dynamics of immunity are crucial to understanding the long-term patterns of the SARS-CoV-2 pandemic. Several cases of reinfection with SARS-CoV-2 have been documented 48–142 days after the initial infection and immunity to seasonal circulating coronaviruses is estimated to be shorter than 1 year. Using an age-structured, deterministic model, we explore potential immunity dynamics using contact data from the UK population. In the scenario where immunity to SARS-CoV-2 lasts an average of three months for non-hospitalized individuals, a year for hospitalized individuals, and the effective reproduction number after lockdown ends is 1.2 (our worst-case scenario), we find that the secondary peak occurs in winter 2020 with a daily maximum of 387 000 infectious individuals and 125 000 daily new cases; threefold greater than in a scenario with permanent immunity. Our models suggest that longitudinal serological surveys to determine if immunity in the population is waning will be most informative when sampling takes place from the end of the lockdown in June until autumn 2020. After this period, the proportion of the population with antibodies to SARS-CoV-2 is expected to increase due to the secondary wave. Overall, our analysis presents considerations for policy makers on the longer-term dynamics of SARS-CoV-2 in the UK and suggests that strategies designed to achieve herd immunity may lead to repeated waves of infection as immunity to reinfection is not permanent.This article is part of the theme issue ‘Modelling that shaped the early COVID-19 pandemic response in the UK’.
Highlights
As of the 1st of July 2020, SARS-CoV-2 has infected at least 10 million people worldwide and resulted in over 500 000 deaths [1,2]
We predict that surveys to detect waning immunity at the population level would be most effective when carried out in the period between the end of lockdown and autumn 2020, as after this point an upsurge in cases is expected that will increase the proportion of the population with immunity to SARS-CoV-2
This will allow evaluation of whether specific antibodies generated against the virus are short-lived if reductions in antibody prevalence are observed at the population level
Summary
As of the 1st of July 2020, SARS-CoV-2 has infected at least 10 million people worldwide and resulted in over 500 000 deaths [1,2]. Recent studies have considered this question for SARS-CoV-2 [27,28], with Britton et al [28] noting that the disease-induced population immunity threshold could be closer to 40% in an age-structured population when R0 is 2.5, rather than the 60% ‘classic’ population immunity threshold This phenomenon is driven by individuals who have more contacts, or greater susceptibility to the virus, getting infected earlier on and leaving the susceptible population, decelerating the growth of the epidemic. The case of reinfection in the USA, in a 25-year-old male from Nevada, was notable for the second infection causing more severe symptoms than the first, and led to the patient requiring supplemental oxygen and hospitalization While these reported cases confirm the biological plausibility of reinfection with SARS-CoV-2, the data are too sparse to infer an expected duration of immunity at the population level
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