Getting infected with the new coronavirus again may not be as rare as previously believed, a new study suggests.
Researchers found that more than ten percent among young Marine Corps recruits who had previously tested positive had a second positive test during a six-week follow-up.
What’s more, the group that became infected again had lower antibody levels than those who were infected for the first time. and most had no detectable neutralizing antibodies against COVID-19.
The team – from the Naval Medical Research Center in Silver Springs, Maryland, and the Icahn School of Medicine at Mount Sinai in New York City – say the findings provide evidence that antibodies caused by an initial infection are largely protective, but does not guarantee. immunity to a subsequent infection.
Researchers looked at 3,249 Marine Corps recruits between the ages of 18 and 20 during a 14-day quarantine and six-week basic training, of which 189 were previously infected with COVID-19 and 2,247 who did not. Pictured: US Marine Recruits Receive Coronavirus Health Examinations at Marine Corps Recruit Depot in San Diego, California, April 2020
More than 10% of the previously infected group underwent a second positive test during basic training (yellow line) and 48% of the non-infected group tested positive (black line)
For the study, published on the pre-print website medRxiv.org, the team used data from the COVID-19 Health Action Response for Marines (CHARM) study.
The study looked at marine newcomers since May 4 and tested them every week for the first two weeks and then every other week thereafter.
A total of 3,249 mostly male marine recruits between the ages of 18 and 20 were tested for coronavirus antibodies upon their arrival for a 14-day period. quarantine.
They were tested for the virus before, in the middle and at the end of the quarantine and then followed up for six weeks and tested fortnightly.
According to researchers, the three negative tests during quarantine helped ensure that infections diagnosed during basic training were not persistent infections, but rather new infections.
Neutralizing antibodies were undetectable in one third of the re-infected group (left) and more than 80% in those who tested positive (right) before quarantine, but not again.
Among the recruits, 189 had previously been infected with COVID-19 before arriving in the quarantine period, and 2,247 had not yet.
The results showed that 19 recruits from the previously infected group, or 10.1 percent, had at least one positive test during the six-week follow-up.
This is much higher than the percentage among the general public, in which only three famous people in the US out of more than 32 million tested positive twice.
By comparison, 1,079 recruits from the uninfected group, equivalent to 48 percent, tested positive during the follow-up period.
“Our results indicate that although antibodies induced by infection are largely protective, they do not guarantee effective immunity against subsequent infection,” the authors wrote.
The team then tested the virus load and the antibody levels among the two groups.
They found that recruits in the newly infected group who tested positive for the first time had ten times higher virus load than those who tested positive again.
In addition, 84.2 percent of the re-infected group was asymptomatic compared with 67.8 percent of the newly infected group.
Surprisingly, perhaps, the antibody levels were the highest among the group for the first time.
The results of the antibody test use different dilutions set at 1: 150, 1: 450, 1: 1350, 1: 4050 or 1: 12150, with each score indicating how many times a scientist can dilute a patient’s blood and still the antibodies.
Titers of 1: 150 were categorized as low; 1: 450 and 1: 350 as moderate; and 1: 4050 or 1: 12150 as high.
The reinfected group had 26 percent in the low range, 57.9 percent in the moderate range, and 15.8 percent in the high range.
By comparison, in the newly infected group, 3.5 percent were in the low range, 76.4 percent in the moderate range, and 20 percent in the high range.
Neutralizing antibodies were also undetectable in six of the 19 recruits – or 31.6 percent – who became infected again.
Even among 54 patients who tested positive before basic training and were not re-infected, 83.3 percent had undetectable neutralizing antibodies.
The team says this study shows the importance of vaccinating those who have never been infected, and those who have been vaccinated before.