Even young and relatively healthy people who have had Covid-19 before should still get a vaccine to prevent re-infection and to slow down the spread of the disease, new research suggests.
The study, published Thursday in the journal the Lancet Respiratory Medicine, found that about 10% of those who had previous infections in the study became reinfected, compared to the 50% of new infections among those who had not had Covid-19 before.
The study was conducted among more than 3,000 otherwise healthy US Marines between May and November of 2020. Most of the people in the study were men between the age of 18 and 20.
For the study, the Marines had an unsupervised two-week quarantine at home before going into a Marine facility that had a supervised quarantine for another two weeks.
The Marines underwent antibody tests at the start of camp to determine if they had prior infection. Nearly 200 had indicators that they had a prior Covid-19 infection, more than 2,200 had no signs of prior infection.
The Marines were given a biweekly PCR test throughout their time in basic training that lasted about six weeks. Across both groups there were more 1,098 new infections during the study, 19 of which had a prior infection.
“Immunity is not guaranteed by past infection, and vaccinations that provide additional protection are still needed for those who have had COVID-19,” said study co-author Dr. Stuart Sealfon, a professor of neurology and pharmacological sciences at the Icahn School of Medicine at Mount Sinai.
There are limits to the study. Researchers were unable to determine the severity of infection among those who had Covid-19 before. Some infections may also have been missed in the period between the bi-weekly PCR testing during the program. Researchers also believe the risk of reinfection would be about the same for other demographics, although the exact rates may vary. Earlier studies among populations that don’t live in such crowded conditions found lower reinfection rates.
A commentary that accompanied the research said that the study showed some “interesting insights” about reinfection.
“These data confirm that seropositive individuals have a significant albeit limited protection for new infections,” the commentary written by Maria Velasco, a researcher at Hospital Universitario Fundación Alcorcón, Spain, said. “Second, the rate of new SARS-CoV-2 PCR detection among seropositive Marines cases is not negligible (1·1 cases per person-year), even in the young and healthy population. Globally, these results indicate that COVID-19 does not provide an almost universal and long-lasting protective immunity such as measles.”
Read More: April 15, 2021 coronavirus news