New evidence suggests that COVID-19 survivors who test positive for antibodies appear to be protected from reinfection for at least a few months.
Researchers found that having coronavirus antibodies gives people a 10 times lower risk of infection compared to those who tested negative for antibodies.
In addition, this protection lasted for at least 90 days after their first antibody test, and in some cases even longer.
The team, from the National Cancer Institute at the National Institutes of Health, the findings are encouraging, but more research is needed to determine how long survivors are protected and whether this protection is threatened by new coronavirus variants spreading across the US.
A new study looked at 3.2 million antibody tests in January 2020 and August 2020 and found that 11.6% tested positive for antibodies against coronavirus and the remaining 88.4% negative. Pictured: A phlebotomist takes blood by finger prick during a COVID-19 antibody test in Pico Rivera, California, February 2021
After at least 90 days, 0.3% of survivors were re-infected with COVID-19 compared to 3% of people who had no antibodies (above, far right)
Antibody tests, also called seropositivity tests, require blood to be drawn through a vein and can only be analyzed in a certified laboratory.
Some tests look for the IgG antibody, a protein that the body makes in the late stages of infection that can persist for months and possibly years after a person has recovered.
Others try to detect the antibody IgM, which is produced by the body a few days after infection.
“The data from this study suggests that people who have a positive result on a commercial antibody test appear to have substantial immunity to SARS-CoV-2, which means they may have a lower risk of future infection,” said lead author Dr. Lynne. Penberthy. , and associate director of NCI’s Surveillance Research Program.
For the study, published in JAMA Internal Medicine, the team looked at data from more than 3.2 million American adults who underwent a COVID-19 antibody test between January 2020 and August 2020.
Of the tests, 11.6 percent, over 378,000, tested positive for antibodies, and the remaining 88.4 percent, over 2.8 million, tested negative.
During a follow-up period of at least 90 days, researchers looked at the data to see how many people had tested positive for a coronavirus infection.
The team noted that a positive antibody test within 30 days of the initial test could be caused by a person still shedding the virus
However, most viral shedding is expected to end after 90 days, so a positive result after three months would likely indicate a new infection.
They found that 0.3 percent of all people who tested positive for antibodies were reinfected with COVID-19, compared to three percent of people who first tested positive and had no antibodies.
“The results of the study are actually a ten-fold reduction, but I would have reservations,” study co-author Dr. Douglas Lowy, chief deputy director of the National Cancer Institute, told CNN.
In other words, it could be an overestimation of the reduction. It could be an underestimate of the reduction.
‘The big message for me is: there is a reduction. The main consideration is that antibody positive after a natural infection is associated with partial protection against a new infection. ‘
The authors say they are encouraged by the results, but that future studies are needed, including how long protection lasts and whether it diminishes over time.
In addition, the study did not compare whether people who were reinfected have high or low levels of antibodies from their first infections.
“Additional research is needed to understand how long this protection lasts, who may have limited protection, and how patient characteristics, such as co-morbid conditions, may affect protection,” Penberthy said.
“Still, we are encouraged by this early finding.”
