Changing risk factors for developing SARS-CoV-2 infection from Delta to Omicron

Abstract

Background: One of the few studies to estimate infection risk with SARS-CoV-2 in the general population was the UK Office of National Statistics Infection Survey. This survey provided data that allowed us to describe and interpret apparent risk factors for testing positive for SARS-CoV-2 in a period when variants and COVID-19 controls experienced large changes.

Method: The ONS published estimates of likelihood of individuals testing positive in two week monitoring periods between 21st November 2021 and 7th May 2022, relating this positivity to social and behavioural factors. We applied meta-regression to these estimates of likelihood of testing positive to determine whether the monitored potential risk factors remained constant during the pandemic.

Results: Some risk factors had consistent relationship with risk of infection (always protective or always linked to higher risk, throughout monitoring period). Other risk factors had variable relationship with risk of infection, with changes seeming to especially correlate with the emergence of Omicron BA.2 dominance. These variable factors were mask-wearing habits, history of foreign travel, household size, working status (retired or not) and contact with children or persons age over 70.

Conclusion: Relevance of some risk factors to likelihood of testing positive for SARS-CoV-2 may relate to reinfection risk, variant infectiousness and status of social distancing regulations.

Fig 1. Risk of testing positive for SARS-CoV-2 by household size compared to households with just a single person.

a. 2 people in household, b. 3 people in household, c. 4 people in household, d. 5 or more people in household.

Fig 2. Risk of testing positive for SARS-CoV-2, with respect to ages of other household members.

a. Adults living with someone age 16 years or younger, b. Adults aged under 70 years and living with someone age 70 years or older.

Fig 3. Risk of testing positive for SARS-CoV-2 when never wearing a face covering, compared to always wearing one.

a. School children in enclosed spaces, b. School children in school, c. Adults in enclosed spaces, d. Adults at school or at work.

Fig 4. Risk of testing positive by rurality, retirement status or recent travel history.

a. Living in urban city or town compared to major urban area, b. Being retired compared to being employed and going to work, c. Travelled abroad in recent 28 days compared to no foreign travel in last 28 days.