The rapidly spreading coronavirus may have already infected half the UK population — but that is encouraging news, according to a new study by the University of Oxford.

The modeling by researchers at Oxford's Evolutionary Ecology of Infectious Disease group indicates the COVID-19 virus reached the UK by mid-January at the latest, spreading undetected for more than a month before the first official case was reported in late February, the Financial Times reports.

But even though this suggests the spread is far worse than scientists previously estimated, it also implies that only one in a thousand people infected with COVID-19 requires hospitalization.

The researchers say this shows that herd immunity — the idea that the virus will stop spreading when enough of the population builds up resistance through becoming infected — can help fight the highly-contagious disease.