It is important for young people to have the Covid vaccine even if they have previously been infected, in order to stop reinfection and onward transmission, researchers have stressed.
A Lancet study involving over 3,000 US Marine recruits aged 18-20, found those who had already had Covid-19 had a 10% risk of reinfection. This compared to an infection rate of 48% among study participants who had not previously had Covid.
The vast majority (84%) of those who were reinfected were asymptomatic or only mildly symptomatic, but the same was also the case for 68% of the study participants who were infected for the first time. None were hospitalised from either group.
The researchers concluded that although antibodies induced by the initial infection are ‘largely protective’, they ‘do not guarantee’ immunity against subsequent infection.
They concluded therefore that ‘vaccination might still be necessary to boost the natural immune response and prevent reinfection and reduce transmission’.
The researchers acknowledged the high rate of infection may not compare with infection levels in wider society given the Marines crowded living conditions and demanding training which ‘might also suppress immunity’.
Senior study author Professor Stuart Sealfon, of Icahn School of Medicine at Mount Sinai, New York, said: ‘Despite a prior Covid-19 infection, young people can catch the virus again and may still transmit it to others. This is an important point to know and remember as vaccine rollouts continue.
‘Young people should get the vaccine whenever possible, since vaccination is necessary to boost immune responses, prevent reinfection, and reduce transmission.’
A large study of NHS staff, published in January, found that antibodies from past Covid-19 infection provide 83% protection against reinfection for at least five months, though the evidence from Public Health England suggested that ‘some of those with antibodies may still be able to pass the virus on’.
In February, a study found that patients who previously had Covid are far more likely to suffer side effects from the Pfizer jab. The researchers said indicated Covid survivors may only need one dose of the vaccine, rather than the current two-dose schedule.
The news comes as the UK has now embarked on the second phase of the Covid vaccination campaign, which will include healthy adults aged 18-49 in order of descending age.