Most who test positive in UK Covid study had earlier infection

About two-thirds of the participants in a large U.K. Covid-19 study who tested positive this month reported a previous infection with the virus, researchers found. 

Another 7.5% said they suspected they’d had an earlier case, according to the React-1 study led by Imperial College London.

Researchers looked at infections among some 100,000 volunteers from Jan. 5 to Jan. 20.

Cases in England reached a record early this month as omicron became the dominant variant, the study also found. Infections among research participants rose to about 4.4% -- a three-fold increase from December. The high proportion who reported earlier cases adds to evidence that omicron can evade at least some of the defenses generated by infection with previous variants. 

Deaths and hospitalizations were lower than in previous waves, even as the prevalence of the virus reached the highest level since the study began in May 2020. The peak of infections occurred around Jan. 5, before cases declined and then leveled off from the middle of the month.

The U.K. has been easing the "Plan B” Covid restrictions that were implemented across England in December when omicron began spreading quickly through the population. People are no longer being asked to work from home, and rules forcing people to wear face masks in shops and on public transport will be dropped. 

"There is good news in our data in that infections had been rapidly dropping during January, but they are still extremely high and may have recently stalled at a very high prevalence,” said Paul Elliott, director of the React program from Imperial’s School of Public Health.

Children aged five to 11 had the highest prevalence across all age groups at 7.81%, with infections rising as they returned to school in January. Researchers also warned that the almost 12-fold increase in prevalence for those over 75 may still lead to increased hospitalizations.

UK Health Secretary Sajid Javid said "it’s reassuring to see Covid-19 infections beginning to slow across the country” as restrictions are being lifted. He acknowledged that cases are still elevated and urged people to get their booster shots.