Vaccination against COVID-19 and societys return to normality in England: a modelling study of impacts of different types of naturally acquired and vaccine-induced immunity

Objectives: To project impacts of mass vaccination against COVID-19, and investigate possible impacts of different types of naturally acquired and vaccine-induced immunity on future dynamics of SARS-CoV-2 transmission from 2021 to 2024 in England. Design: Deterministic, compartmental, discrete-time Susceptible-Exposed-Infectious-Recovered (SEIR) modelling. Participants: Population in England. Interventions: Mass vaccination programmes. Outcome measures: Daily and cumulative number of deaths from COVID-19. Results: If vaccine efficacy remains high (85%), the vaccine-induced sterilising immunity lasts ≥182 days, and the reinfectivity is greatly reduced (by ≥60%), annual mass vaccination programmes can prevent further COVID-19 outbreaks in England. Under optimistic scenarios, with annual revaccination programmes, the cumulative number of COVID-19 deaths is estimated to be from 130 000 to 150 000 by the end of 2024. However, the total number of COVID-19 deaths may be up to 431 000 by the end of 2024, under scenarios with compromised vaccine efficacy (62.5%), short duration of natural and vaccine immunity (365/182 days) and small reduction in reinfectivity (30%). Under the assumed scenarios, more frequent revaccinations are associated with smaller total numbers and lower peaks of daily deaths from COVID-19. Conclusions: Under optimistic scenarios, mass immunisation using efficacious vaccines may enable society safely to return to normality. However, under plausible scenarios with low vaccine efficacy and short durability of immunity, COVID-19 could continue to cause recurrent waves of severe morbidity and mortality despite frequent vaccinations. It is crucial to monitor the vaccination effects in the real world, and to better understand characteristics of naturally acquired and vaccine-induced immunity against SARS-CoV-2.