Researchers at the University of Hong Kong have recorded what they said was the first genetically proven case of Covid-19 reinfection, four and a half months after the patient originally caught the virus.

The 33-year-old man was hospitalised with moderate Covid-19 symptoms in Hong Kong in March, then tested positive again in August when he was screened at Hong Kong airport on returning from a trip to Spain. On the second occasion he displayed no symptoms of infection.

The researchers proved that he had been reinfected — and that the coronavirus had not simply remained in his body — by taking genetic fingerprints on each occasion. These showed that the second virus had 24 differences from the first — more than could have occurred through mutations within one individual.