Background
High prevalence of SARS-CoV-2 virus in many northern hemisphere populations is causing
extreme pressure on healthcare services and leading to high numbers of fatalities. Even
though safe and effective vaccines are being deployed in many populations, the majority of
those most at-risk of severe COVID-19 will not be protected until late spring, even in
countries already at a more advanced stage of vaccine deployment.

Methods
The REal-time Assessment of Community Transmission study-1 (REACT-1) obtains throat
and nose swabs from between 120,000 and 180,000 people in the community in England at
approximately monthly intervals. Round 8a of REACT-1 mainly covers a period from 6th
January 2021 to 15th January 2021. Swabs are tested for SARS-CoV-2 virus and patterns of
swab-positivity are described over time, space and with respect to individual characteristics.
We compare swab-positivity prevalence from REACT-1 with mobility data based on the GPS
locations of individuals using the Facebook mobile phone app. We also compare results
from round 8a with those from round 7 in which swabs were collected from 13th November
to 24th November (round 7a) and 25th November to 3rd December 2020 (round 7b).

Results
In round 8a, we found 1,962 positives from 142,909 swabs giving a weighted prevalence of
1.58% (95% CI, 1.49%, 1.68%). Using a constant growth model, we found no strong
evidence for either growth or decay averaged across the period; rather, based on data from
a limited number of days, prevalence may have started to rise at the end of round 8a.
Facebook mobility data showed a marked decrease in activity at the end of December 2020,
followed by a rise at the start of the working year in January 2021. Between round 7b and
round 8a, prevalence increased in all adult age groups, more than doubling to 0.94%
(0.83%, 1.07%) in those aged 65 and over. Large household size, living in a deprived
neighbourhood, and Black and Asian ethnicity were all associated with increased
prevalence. Both healthcare and care home workers, and other key workers, had increased
odds of swab-positivity compared to other workers.

Conclusion
During the initial 10 days of the third COVID-19 lockdown in England in January 2021,
prevalence of SARS-CoV-2 was very high with no evidence of decline. Until prevalence in
the community is reduced substantially, health services will remain under extreme pressure
and the cumulative number of lives lost during this pandemic will continue to increase
rapidly.