When the UK went into lockdown in March 2020, there were many unknowns about how SARS-CoV-2 would spread through the population. But what scientists did know was that effective surveillance would be critical to understanding disease rates and spread, and to mitigating the impact of the virus. We spoke to Graham Blakoe, a Project Manager at Imperial College London, who is working closely on the REal-time Assessment of Community Transmission (REACT) Programme, one of the national studies to which COG-UK has contributed.
In the early days of the COVID-19 pandemic, infection rates in the population were mostly based on people who developed symptoms and as a result, underwent testing to detect SARS-CoV-2. But that only provided part of the picture. What the UK Government also needed to know to make informed public health decisions was the prevalence of COVID-19 in the asymptomatic population – those who were infected and at risk of spreading the virus but showed no symptoms.
As a result, in April 2020 Imperial College London and Ipsos MORI were commissioned to carry out the REal-Time Assessment of Community Transmission (REACT) programme.
The programme initially focused on measuring the prevalence of COVID-19 in the general UK population, by randomly selecting and inviting up to 800,000 individuals to achieve a sample size of at least 100,000 who provided a swab for a PCR test (REACT-1). In all, over 3 million people took part in REACT-1 over the 19 discrete rounds of the study.
“The key differentiator for REACT is that we chose a sample of the population that was truly representative”, says Graham. “The sampling method ensured the data generated accurately represented the whole population.”
Data from REACT-1 were used to estimate how many people in England were infected with the virus, which in turn told us how quickly the virus was spreading. The data were also used to look at infection trends by geography and other risk factors – such as age, ethnicity and occupation.
“As time went on, it became increasingly important to step up genome sequencing of positive samples, especially as more variants of concern began to circulate”, says Graham. Genome data are key to tracking any changes in transmission or disease severity of variants. Then, as vaccines became available, REACT-1 also began to estimate the effectiveness of vaccination against SARS-CoV-2infection. The relationship with COG-UK was critical in obtaining rapid viral genome sequencing, which gave real-time information on emerging variants as they appeared in the population.
A second workstream, REACT-2, also a collaboration between Imperial College London, Ipsos MORI and the UK Government, took things further. Where the original study looked at the distribution of the virus in real time, scientists now sought to measure the prevalence of antibodies to SARS-CoV-2 in a representative sample of the adult population in England.
“This would show who had been infected since the beginning of the pandemic, helping to identify people that may not have known they had been infected,” explains Graham.
From June 2020 to May 2021, over 900,000 people took part in REACT-2, which helped indicate how many people in the UK had already been infected with the virus – and identify those most at risk. It also highlighted the waning of antibodies against SARS-CoV-2 over time, and the impact of vaccination on antibody prevalence in the population.
Ahead of the vaccine rollout there were hopes that a large proportion of the population would already have some level of immunity to the virus from natural infection, but the study found that only 7% of the population had measurable antibodies against SARS-CoV-2 after the first wave of infections.
“The data collected as part of REACT-1 and REACT-2 were instrumental in the UK Government making informed decisions, and fed directly into public health efforts”, says Graham. The two studies also highlighted the unequal burden of COVID-19, with individuals living in deprived areas, or not being able to work from home, found to be more likely to have been infected.
The REACT programme has since been extended to include two further workstreams REACT GE and REACT Long COVID.
These studies look for biological ‘signatures’ in over 10,000 people that may explain why some people experience severe symptoms of COVID-19, while some do not. REACT Long COVID is an extension of REACT GE, which will involve more than 120,000 people to understand why some will have persistent symptoms for prolonged periods of time – now commonly known as ‘long COVID’.
“What we have from across the REACT programme is a cohort of around 2.5 million people, who have agreed to be contacted for future research and link their health data to our records,” says Graham. “With the linkage of health data, we can monitor people as part of the long COVID study and contact them for future programmes.”
To find out more about the REACT programme, please click here.
