Young people who have already tested positive for coronavirus are not fully protected against reinfection, new research suggests.
A study of 3,000 members of the US Marine Corps, mostly aged between 18 and 20, showed that 10% of participants (19 out of 189) who had contracted COVID-19 before tested positive again.
This is compared with 50% of people who had not had coronavirus previously (1,079 out of 2,247).
The researchers behind the study, which was carried out between May and November 2020 and published in The Lancet Respiratory Medicine journal, say it highlights the risk of COVID reinfection in young people.
They added that only vaccination will help reduce severe disease or death from the virus – and possibly transmission.
But they stressed that there were limitations to the study, including the crowded living conditions of the military base where it was carried out and close contact required to carry out participants’ training.
This could have contributed to a higher reinfection rate than in the rest of the population, they said.
Professor Stuart Sealfon, of Icahn School of Medicine at Mount Sinai, New York, and senior author of the study, said: “As vaccine rollouts continue to gain momentum it is important to remember that, despite a prior COVID-19 infection, young people can catch the virus again and may still transmit it to others.
“Immunity is not guaranteed by past infection, and vaccinations that provide additional protection are still needed for those who have had COVID-19.”
Similar studies in other countries have shown high levels of protection against reinfection from past infections.
In Denmark, for example, a study of four million people showed that only 0.65% of those who tested positive during the country’s first wave contracted the virus again in the second wave.
The research suggested that risk of infection was five times higher (3.3%) for people who had not already had the disease.
A UK study of NHS workers also showed that they were five times more likely to get coronavirus if they hadn’t already tested positive.
All the participants in the US Marine study had no underlying health conditions.