A man walks through fallen leaves beside a wall covered in hand-drawn hearts and messages commemorating COVID victims in London

A wall in London commemorates people who died of COVID-19.Credit: Toby Melville/Alamy/Reuters

The COVID-19 pandemic in the United Kingdom has often foreshadowed what came later elsewhere. The highly contagious Alpha variant was first detected there, and the country then reported high caseloads of the more-contagious Delta strain before this variant dispersed around the rest of the world. The United Kingdom also saw a wave of infections that seems to have preceded a similar glut now sweeping Western Europe.

Furthermore, England was among the first regions in Western Europe to lift almost all of its COVID-19 restrictions, following one of the world’s fastest vaccine roll-outs. It ended the legal requirements for social distancing and mask use on 19 July, with Wales and Scotland — which set their own public-health policies — lifting most of their restrictions on 7 and 9 August, respectively. Northern Ireland followed on 31 October.

As one of the first countries to trust high vaccine coverage and public responsibility alone to control the spread of SARS-CoV-2, the United Kingdom has become a control experiment that scientists across the world are studying. “We are watching the increase in cases closely, trying to dissect what is going on and how that might influence our situation right now,” says Rafael Radi, a biochemist and coordinator of Uruguay’s COVID-19 Scientific Advisory Group.

Nature spoke to scientists around the world about what they hope to learn from the UK experience.

Can vaccines alone prevent infections from surging?

The United Kingdom was hit by three million infections between July and October this year — comparable to when the country was under a strict lockdown in late 2020. This is despite 79.5% of those aged 12 years and older having received two vaccine doses as of 31 October.

UK infection rates are higher than those in countries in continental Europe, where COVID-19 restrictions were relaxed later or remain in place. In the 7 days between 17 October and 23 October, Spain recorded 286 infections per one million people, and Germany 1,203. The United Kingdom registered 4,868 over the same week.

The surge in infections shows that vaccines alone cannot contain the virus, say scientists calling for the introduction of ‘soft’ public-health measures to avoid another lockdown.

“The vaccines are amazing and doing exactly what they’re supposed to do,” says Susan Butler-Wu, director of medical microbiology at the LAC+USC Medical Center in Los Angeles, California. “But why don’t we want to give them the best chance by combining them with other measures?”

Was the behaviour of individuals responsible for the recent surge?

The surge in infections is not the result of the public suddenly abandoning caution, researchers say. “We have not seen a continuous rise [in social interaction], but rather a small increase and then fluctuations driven by whether schools are open and how many people are attending work,” says Christopher Jarvis, a statistician who heads the London School of Hygiene & Tropical Medicine’s CoMix Social Contact Survey.

The average adult now has contact with three to four other people per day, compared with more than ten before the pandemic. For children, the numbers are much higher now that schools have reopened. Mask use dropped once the mandate was lifted, but this is harder to measure.

The gradual pace of behaviour readjustment could explain why the country has experienced a sustained high level of infections rather than the spike that models predicted in August or September. Ongoing high transmission suggests that measures such as free rapid COVID-19 testing will not contain infections while high-risk events in crowded indoor environments are permitted, says William Hanage, an epidemiologist at the Harvard T. H. Chan School of Public Health in Boston, Massachusetts.

“This shows how cautious we need to be with the return to normality,” says Radi. “Increasing human interactions, even with a high proportion of the population fully vaccinated, may lead to new surges, hospitalizations and death.” Uruguay is using the United Kingdom’s rise in infections as a cautionary tale to warn people of the risk of easing restrictions prematurely, Radi says.

Is vaccine protection waning?

The United Kingdom had one of the fastest COVID-19 vaccination campaigns in Europe. But that strength now seems to be its Achilles heel. The country’s first COVID-19 vaccines were administered ten months ago, and antibodies have had time to decline.

Vaccine effectiveness against infection, hospitalization and death fell considerably after six months, particularly in older people, a UK-based study has found1. A separate study in Israel — another country that deployed vaccines early — found similar results2.

One of the driving forces behind this might have been dropping antibody levels, says Paul Hunter, who studies health protection and medicine at the University of East Anglia in Norwich, UK. Despite high infection rates and the ongoing vaccination campaign, antibody levels plateaued in May and then began to drop, according to the UK Office for National Statistics.

A decline in infection-blocking, or ‘neutralizing’, antibodies does not mean that someone is susceptible to infection, because memory immune cells also play a part, “but we do know that the level of neutralizing antibodies early on is a good indicator of protection”, Hunter says.

But are vaccines are still holding up against death and serious illness?

The Delta variant’s mutations — combined with waning vaccine antibodies — are causing more breakthrough infections. But vaccines are still offering remarkable protection against hospitalization and death. A study at the University of Edinburgh, UK, found that the Pfizer–BioNTech and Oxford–AstraZeneca vaccines were 90% and 91% effective, respectively, at preventing death3. Furthermore, around 75,000 people required hospital treatment for COVID-19 in the United Kingdom between the start of July and early October this year, compared with 185,000 between October 2020 and January 2021, when the number of infections was comparable but vaccines were less available.

Relative to the size of its population, the United Kingdom has around three times as many infections as the United States, but only two-thirds the daily deaths. “The amount of infection that is currently going on in the UK would be expected to have much worse consequences if replicated elsewhere,” says Hanage.

Can boosters help to control future surges?

UK authorities began offering a third dose of the COVID-19 vaccines to residents aged 50 years and older, and to those in high-risk groups, on 16 September. Although the precise impact of booster doses has not been established, “the emerging evidence is that they are a lot more effective at reducing infections than we were expecting”, says Hunter.

A study at the Weizmann Institute of Science in Rehovot, Israel, found that people who received a third dose of the Pfizer–BioNTech vaccine were almost 20 times less likely to get seriously ill from COVID-19, and 10 times less likely to be infected, than were people who had received their second and last dose at least 5 months before4.

The World Health Organization has criticized the roll-out of third doses in wealthy nations when many people in poorer ones are yet to receive their first. But boosters could get the United Kingdom through the coming winter without new restrictions being imposed, says Marc Baguelin, who models COVID-19 infections for the UK government at Imperial College London. His team’s most optimistic models — based on assumptions regarding behaviour and the effectiveness of immunity — predict a sustained high number of infections between October 2021 and March 2022, leading to around 43,000 hospital admissions and more than 5,000 deaths.

High circulation of the virus, as the cold pushes people indoors where the virus spreads more easily, and as immunity wanes, means that marginal increases in vaccine protection should have “a significant impact on hospitalizations and deaths”, Baguelin says. “Now everything relies on the boosters.”