Learning from the pandemic in real-time

Three million, four hundred and eighteen thousand, seven hundred and eighty-eight.

Since Imperial’s REACT study began little over two years ago, that’s the number of people up and down the country who’ve taken part in the programme, swabbing their noses for the virus or pricking their fingers to see if they’d likely had it before.

That makes it one of the world’s largest coronavirus surveillance studies, and the biggest unique study participant group in existence in the country.

While lateral flow antigen tests later became a staple in most households, after they were made freely available by the Government for people to check if they were likely infectious, mass antibody testing at the scale REACT achieved had never been attempted before. Soon after REACT-2 was launched, it began testing around 150,000 people every six weeks for coronavirus antibodies. Preceding this was a major public involvement effort to design the information and materials that came with the testing kits, to ensure that people could understand them and carry out the tests correctly. This was run in parallel to a rigorous scientific evaluation of different available testing kits to find out which ones were the most accurate, usable, and available at scale, working with NHS partners.

“This was a magnificent effort, because we were using technology that hadn’t been tested for this purpose before,” Prof Elliott says. “We were able to get information on population antibody levels on hundreds of thousands of people within just a few days; there was no waiting around for test results. This has been a hugely underestimated approach, but we showed its potential as a valuable population surveillance tool.”

REACT-2 yielded insights far beyond tracing the virus’ footsteps in the population, as we will see later.

REACT-1 collected data over a roughly two-week period each month (called a round, of which there were 19 in total). Each of these rounds offered a near real-time snapshot of where the virus was in the population at that time. This provided a vital early warning system, detecting the earliest signals of proceeding surges driven by new variants.

“When things changed very quickly, we picked it up,” Prof Elliott says. “We detected early each successive variant-driven wave, firstly when the Alpha variant began to take over the original strain of the virus. We could see a rise in infections in Essex, Kent and South London as a ‘canary in the coal mine’ marker of what was happening.

“And then when we detected just two cases of the Delta variant, that was one of the first signals that a new wave was coming. Next it was Omicron rapidly taking over from Delta last December, and then most recently the rise of the BA.2 Omicron offshoot in March."

Watch these rises in prevalence from December 2021 to March 2022 in the heat maps below.

“Each time, we could see these trends happening in our data in real-time," he adds. "And if there’s one thing we’ve learnt from this, it’s that the virus is really unpredictable. Continued surveillance is vital to stay on top of the numbers and spot the next variant if and when it comes along.”

Watch Omicron taking over from Delta below.

By rapidly feeding this information to Government, REACT helped enable policymakers to make evidence-based public health decisions in a timely way. Similarly, by quickly getting findings out to the public, REACT helped people make informed decisions about their behaviours and weigh up the risks of their actions.

Early in the pandemic, it soon became clear that the burden of the virus was not falling on everyone equally. Not just in the UK but in other countries too. People from minority ethnic communities were disproportionately impacted by COVID-19, with hospitalisation and death rates higher in Black and Asian people compared with White people in the UK. This led to speculation about the underlying reasons. Was this because White people had better access to care, or perhaps some biological differences that meant people from ethnic minority backgrounds experienced the disease differently? Both of these ideas were touted, but REACT helped to show that neither were likely explanations.

Antibodies offer a long-lasting record of past exposure to the virus, enabling analyses of the timing and extent of the epidemic. As vaccines weren’t available at this stage of the pandemic, the presence of antibodies indicated past infection and not immunisation. So the team could use data from their REACT-2 antibody survey to look at the burden of infection, and link this to both their questionnaire data covering important demographic information like occupation and household size, and also to hospitalisation and death rates.

Using data until mid-July 2020, the team discovered that the rate of infected people dying – infection fatality ratio – was similar across ethnicities, yet people of Black or Asian ethnicity had two-three-times higher infection rates compared to White people. This was a hugely important finding, suggesting that rather than down to different experiences of the disease or care, the higher burden in minority ethnic communities was likely due to higher exposure to the virus. These trends could be linked to other factors such as people from minority ethnic communities being more likely to live in larger households, or be employed as key workers.

These findings were significant, not only because they challenged the idea of some underlying biological differences, but also because they highlighted the need to work with at risk groups to identify appropriate and effective strategies to reduce these inequalities.

“We’ve been able to identify people at risk and empower people to make decisions on their own behaviours, including whether or not they choose to get vaccinated,” says REACT scientist Professor Christl Donnelly from the School of Public Health.