According to a new study, re-infection with the new coronavirus may not be as rare as previously thought.
The researchers found that among the young Marine Corps recruits who had previously tested positive, more than 10 percent had a second positive test during a six-week follow-up.
In addition, the re-infected group had lower antibody levels than those who were first infected. and most lacked detectable neutralizing antibodies against COVID-19.
The team, from the Naval Medical Research Center in Silver Springs, Maryland, and the Icahn School of Medicine in Mount Sinai, New York City, says the findings provide evidence that antibodies are induced by an initial infection. they are largely protective, but do not guarantee immunity against a subsequent infection.
The researchers examined 3,249 Marine Corps recruits between the ages of 18 and 20 over a 14-day quarantine and a six-week basic training, 189 of whom had previously been infected with COVID-19 and 2,247 who had not. Pictured: U.S. Marine Recruits Receive Coronavirus Health Tests at Marine Corps Recruitment Depot in San Diego, California, April 2020
More than 10% of the previously infected group had a second positive test during basic training (yellow line) and 48% of the uninfected group tested positive (black line)
For the study, published on the prepress site medRxiv.org, the team used data from the COVID-19 Health Action Response for Marines (CHARM) study.
The study examined Navy newcomers since May 4, testing them weekly for the first two weeks and then every two weeks.
A total of 3,249 mostly male male recruits between the ages of 18 and 20 were tested for coronavirus antibodies on arrival for 14 days. quarantine.
The virus was tested before, in the middle and at the end of the quarantine and then monitored for six weeks, with a fortnightly test.
The researchers say the three negative tests during quarantine helped ensure that the infections diagnosed during basic training were not persistent infections, but new infections.
Neutralizing antibodies were not detectable in one-third of the reinfected group (left) and more than 80% in those that tested positive (right) before quarantine, but not again.
Among the recruits, 189 had been previously infected with COVID-19 before reaching the quarantine period and 2,247 had not.
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 well above the general public rate, in which only three well-known people in the U.S. over 32 million have tested positive twice.
In comparison, 1,079 recruits from the uninfected group, equivalent to 48%, tested positive during the follow-up period.
“Our results indicate that while infection-induced antibodies are largely protective, they do not guarantee effective immunity against subsequent infection,” the authors wrote.
The team then tested viral loads and antibody levels between the two groups.
They found that recruits from the newly infected group who tested positive for the first time had 10 times higher viral loads than those who tested positive again.
In addition, 84.2% of the reinfected group was asymptomatic compared to 67.8% of the newly infected group.
But, surprisingly, antibody levels were the highest among the groups that tested positive for the first time.
The results of the antibody tests used different dilutions set at 1: 150, 1: 450, 1: 1350, 1: 4050 or 1: 12150, with each score indicating the number of times a scientist can dilute the blood. of a patient and still be able to detect the presence of antibodies.
Titles of 1: 150 were classified 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.
In comparison, in the newly infected group, 3.5% were in the low range, 76.4% in the moderate range, and 20% in the high range.
Neutralizing antibodies were also not detected in six of the 19 recruits (31.6%) who were reinfected.
Even among 54 patients who tested positive before basic training and did not become infected again, 83.3 percent had undetectable neutralizing antibodies.
The team says this study demonstrates the importance of vaccinating both those who have never been infected and those who have not been.