Study assess prevalence of SARS-CoV-2 in England after third national lockdown

The alarmingly high infection rate of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the causal agent of the coronavirus 2019 (COVID-19) pandemic, has had an enormous impact on healthcare in many parts of the world. The surge in the rate of hospitalization, especially intensive care unit admissions, has placed an overwhelming burden on healthcare systems worldwide. Among many initiatives to contain the spread of the virus, social distancing, nationwide lockdowns, and vaccine deployments have taken the front seat.

Many European countries, as of spring 2021, are undergoing the third wave of the COVID-19 pandemic. These nations have started following stringent social distancing measures in response. In England, researchers found that since January 2021, the country's third national lockdown, the rate of hospitalization and deaths owing to COVID-19 has been consistently decreasing. On the 8^th of March 2021, the first significant relaxation of lockdown was announced, whereby schools were re-opened. Since then, researchers observed that the rate of decline of new cases had slowed considerably. Following the re-opening of schools, large-scale COVID-19 testing for school children and their families has been conducted with the help of lateral flow devices.

Study: REACT-1 round 10 report: Level prevalence of SARS-CoV-2 swab-positivity in England during third national lockdown in March 2021. Image Credit: NIAID / Flickr

The Real-time Assessment of Community Transmission-1 (REACT-1) is an ongoing study that is helping monitor the rate of SARS-CoV-2 infection in England over time. REACT-1 has significantly boosted the surveillance data in England. It involves the detection, via swab-positivity for SARS-CoV-2, among a random sample of the community irrespective of individuals' COVID-19 symptoms. A new study published on the medRxiv* preprint server focuses on the results from round 10 of REACT-1, which is based on the swabs collected between the 11^th and 30^th of March 2021. In this study, researchers have compared the results of round 10 with round 9, for which samples were collected between the 4^th and 23^rd of February 2021.

While studying the prevalence of infection, the tenth round showed a reduction by around 60%, in comparison to the ninth round. These rounds happened during England's third national lockdown, after the second wave of COVID-19 in the country.

The current research found that the national R number over the period of study was below one, indicating the epidemic had decelerated from February to March. However, the newest data revealed that following the re-opening of school in March, the rate of decline slowed. Further, the frequency of COVID-19 positive individuals plateaued at 1 in 500 (0.20%) people.

Researchers observed the highest prevalence in children belonging to primary and early secondary school, aged between 5-12 years. On the contrary, individuals above the age of 65 years showed the lowest prevalence of COVID-19. Scientists believe that the infection rate is consistently lower among older adults owing to being the primary group to be vaccinated. Further, a decrease in mortality rate and the number of individuals requiring hospitalization, after the onset of vaccination programs, was observed. Scientists also highlighted that post-vaccination, the rate of severe COVID-19 has decreased significantly in the older adult population.

In this study, scientists observed a close proximity between the incidence of COVID-19 measured by the recent rounds of REACT-1 and the data obtained from publicly available sources on the rate of hospital admission and mortality. They found that the relationship, between the prevalence of infections and mortality (suitably lagged) has diverged. Such a divergence could be owing to the vaccination program. This result is consistent with the studies conducted in Israel and Scotland. These countries have also reported high efficiency of vaccines against severe COVID-19.

Scientists believe that in the future, the association between infections, deaths, and hospitalizations in England should be closely monitored. This is because if the approximation of the infection and mortality curves falls back to the previous pattern, it would mean an increase in the emergence of SARS-CoV-2 variants that are evading the vaccine-induced immune response. In the preliminary rounds of REACT-1, the correlation between infections and mortality had appeared to be weaker, possibly owing to the lack of community transmission.

The current study reported swab positivity to be over 30-times higher in participants who were in direct contact with a confirmed COVID-19 patient than in individuals who were not in direct contact. This observation emphasizes the value of COVID-19 testing. Researchers believe that manual contact tracing might not be sufficient to achieve an R number less than 1. Additionally, owing to a consistently higher rate of infection in deprived neighborhoods, REACT-1 recommended highly local interventions even when the number of cases is low.

The government in England is following a new cautious approach for easing the national lockdown. They have adopted the strategy to ease lockdown gradually by implementing an approximate gap of five weeks after each step towards "normalization." This approach ensures time to assess the effect of each step based on the rate of transmission of the virus and the R number. Subsequent REACT-1 surveys will test the efficacy of this strategy.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Dr. Priyom Bose

Priyom holds a Ph.D. in Plant Biology and Biotechnology from the University of Madras, India. She is an active researcher and an experienced science writer. Priyom has also co-authored several original research articles that have been published in reputed peer-reviewed journals. She is also an avid reader and an amateur photographer.