Voluntary risk mitigation behaviour can reduce impact of SARS-CoV-2: a real-time modelling study of the January 2022 Omicron wave in England

• Published in: BMC medicine Vol. 21; no. 1; pp. 25 - 12
• Main Authors: Brooks-Pollock, Ellen, Northstone, Kate, Pellis, Lorenzo, Scarabel, Francesca, Thomas, Amy, Nixon, Emily, Matthews, David A, Bowyer, Vicky, Garcia, Maria Paz, Steves, Claire J, Timpson, Nicholas J, Danon, Leon
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 19.01.2023; BioMed Central; BMC
• Subjects: Age; Behavior; Behavior therapy; Behaviour change; Biobanks; Child; Cohort analysis; Coronaviruses; COVID-19; COVID-19 - epidemiology; COVID-19 - prevention & control; COVID-19 vaccines; Disease transmission; Effectiveness; England - epidemiology; Epidemics; Estimates; Fatalities; Health planning; Households; Humans; Impact prediction; Infections; Infectious disease modelling; Longitudinal Studies; Omicron variant; Pandemics; Patient outcomes; Planning; policy; Probabilistic models; Public health; Real time; Reproduction; Risk management; Risk taking; SARS-CoV-2; Scenario modelling; Severe acute respiratory syndrome coronavirus 2; Shelter in place; Surveys; Uncertainty; United States; Vaccination; Vaccine efficacy; Vaccines; Viral diseases; England; United States; United Kingdom; United Kingdom > UK; Longitudinal cohort studies; Omicron variant; SARS-CoV-2; Interventions; Infectious disease modelling; Scenario modelling; Behaviour change; policy
• ISSN: 1741-7015; 1741-7015
• DOI: 10.1186/s12916-022-02714-5

Predicting the likely size of future SARS-CoV-2 waves is necessary for public health planning. In England, voluntary "plan B" mitigation measures were introduced in December 2021 including increased home working and face coverings in shops but stopped short of restrictions on social contacts. The impact of voluntary risk mitigation behaviours on future SARS-CoV-2 burden is unknown. We developed a rapid online survey of risk mitigation behaviours ahead of the winter 2021 festive period and deployed in two longitudinal cohort studies in the UK (Avon Longitudinal Study of Parents and Children (ALSPAC) and TwinsUK/COVID Symptom Study (CSS) Biobank) in December 2021. Using an individual-based, probabilistic model of COVID-19 transmission between social contacts with SARS-CoV-2 Omicron variant parameters and realistic vaccine coverage in England, we predicted the potential impact of the SARS-CoV-2 Omicron wave in England in terms of the effective reproduction number and cumulative infections, hospital admissions and deaths. Using survey results, we estimated in real-time the impact of voluntary risk mitigation behaviours on the Omicron wave in England, if implemented for the entire epidemic wave. Over 95% of survey respondents (N  = 2686 and N  = 6155) reported some risk mitigation behaviours, with vaccination and using home testing kits reported most frequently. Less than half of those respondents reported that their behaviour was due to "plan B". We estimate that without risk mitigation behaviours, the Omicron variant is consistent with an effective reproduction number between 2.5 and 3.5. Due to the reduced vaccine effectiveness against infection with the Omicron variant, our modelled estimates suggest that between 55% and 60% of the English population could be infected during the current wave, translating into between 12,000 and 46,000 cumulative deaths, depending on assumptions about severity and vaccine effectiveness. The actual number of deaths was 15,208 (26 November 2021-1 March 2022). We estimate that voluntary risk reduction measures could reduce the effective reproduction number to between 1.8 and 2.2 and reduce the cumulative number of deaths by up to 24%. Predicting future infection burden is affected by uncertainty in disease severity and vaccine effectiveness estimates. In addition to biological uncertainty, we show that voluntary measures substantially reduce the projected impact of the SARS-CoV-2 Omicron variant but that voluntary measures alone would be unlikely to completely control transmission.