Testing positive for COVID-19 antibodies confers protection against the virus, an original investigation published online today in Journal of the American Medical Association shows.
“In this cohort study, patients with positive antibody test results were initially more likely to have positive nucleic acid amplification test (NAAT) results, consistent with prolonged RNA shedding, but became markedly less likely to have positive NAAT results over time, suggesting that seropositivity is associated with protection from infection,” the authors concluded. “The duration of protection is unknown, and protection may wane over time.”
Despite all the COVID-19 related research published in recent months, the question of whether testing positive for the antibodies confers protection has lingered. Some people have tested positive for the COVID-19 antibodies without testing positive for the virus. Some developed COVID-19 symptoms after testing positive for the antibodies and some did not.
Some people have not been able to confirm an antibody test with a COVID-19 test due to lack of availability of tests.
“Since the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in late 2019, limited research has shown that the majority of patients who clear their infections develop serum antibodies against the virus that last for at least several months but may decline over time,” the authors explained. “Although it has been speculated that the development of antibodies may be associated with a decreased risk of reinfection, the evidence for this hypothesis is limited and often anecdotal.”
The study published today changed that.
Patients who test positive for antibodies younger
Lead author Raymond Harvey of Aetion, Inc. and colleagues examined records of more than three million Americans tested for antibodies. The tests came from commercially available products.
“In this cohort study of more than 3.2 million US patients with a SARS-CoV-2 antibody test, 0.3 percent of those indexed with positive test results had evidence of a positive nucleic acid amplification test beyond 90 days after index, compared with 3.0 percent indexed with negative antibody test results,” the authors observed.
In other words, “Individuals who are seropositive for SARS-CoV-2 based on commercial assays may be at decreased future risk of SARS-CoV-2 infection,” the authors concluded.
The study sample was 58 percent female with a median age of 48 years. More than 88 percent had a negative antibody result, and 11.6 tested positive.
Patients who tested negative for antibodies were older than those with a positive result (median age of 48 v. 44)
Of those who tested positive, 18.4 percent converted to seronegative over the follow-up periods of 30, 60, and 90 days.
Nobody knows how long protection lasts
In an accompanying editor’s note, Dr. Mitchell Katz discusses how to talk with patients who test positive for antibodies about the study’s results.
“Antibody tests, in this study, appeared accurate and the antibodies protective,” Katz wrote. “Their findings are consistent with a study of health care workers that found that the incidence of SARS-CoV-2 infection in 1,265 workers with anti-spike antibodies was 0.13 per 10,000 days at risk, compared with 1.09 for 11,364 workers who were seronegative for these antibodies.”
Nobody knows how long the protection lasts, however. For that reason, everyone should be vaccinated, Katz said.
“How long the antibody protection provided by vaccines will last is also unknown,” he concluded. “To know how long protection will last with antibodies because of natural infection or vaccination is something only time will tell.”
The study could have implications on future vaccine development. “Understanding the effect of serum antibodies to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on susceptibility to infection is important for identifying at-risk populations and could have implications for vaccine deployment,” the authors concluded.