Study: Antibodies appear to provide protection against COVID-19 reinfection

Patients with COVID-19 antibodies appear to be protected against reinfection for at least a few months, according to research published JAMA Internal Medicine.

In the study, researchers observed lower rates of positive nucleic acid amplification tests (NAATs) among patients who previously tested positive for COVID-19 antibodies than those who tested negative.

“The data from this study suggest that people who have a positive result from a commercial antibody test appear to have substantial immunity to SARS-CoV-2, which means they may be at lower risk for future infection,” Lynne Penberthy, MD, MPH, associate director of the National Cancer Institute’s Surveillance Research Program, who led the study, said in a press release. “Additional research is needed to understand how long this protection lasts, who may have limited protection, and how patient characteristics, such as comorbid conditions, may impact protection. We are nevertheless encouraged by this early finding.”

Penberthy and colleagues conducted a retrospective observational descriptive cohort study using deidentified data from commercial laboratory tests, medical and pharmacy claims, EHRs and hospital charging accounts. The researchers examined patient records from December 2018 through August 28, 2020, to identify patients who received SARS-CoV-2 antibody tests from January 2020 through the end of the study period.

Patients were categorized based on the timing of their first SARS-CoV-2 antibody test result. They were followed through the end of the study period, during which time the researchers identified additional antibody tests or NAATs.

The researchers noted that a positive NAAT result within 30 days of a positive SARS-CoV-2 antibody test is likely caused by viral shedding. But because most viral shedding is expected to end after 90 days, positive NAAT results during this period may indicate a new infection.

The researchers identified 3,257,478 patients who completed an antibody test. Among them, 88.3% initially had negative index antibody results, 11.6% initially had positive index antibody results and 0.1% had inconclusive antibody test results. Of the patients with positive antibody test results, 18.4% became seronegative during the follow-up period.

In patients who initially had positive antibody results, 11.3% had positive diagnostic NAAT results within 30 days of their antibody test. This percentage dropped to 2.7% after 31 to 60 days of the antibody test, 1.1% after 61 to 90 days, and 0.3% more than 90 days after the antibody test.

Among patients who initially had negative antibody results, 3.9% had positive NAAT results within 30 days. According to Penberthy and colleagues, the proportion of patients who initially tested negative for SARS-CoV-2 antibodies and later tested positive with a NAAT was approximately 3% throughout the follow-up period, even past 90 days.

Penberthy and colleagues determined that, compared with those who initially tested negative for antibodies, the ratio of positive NAAT results among those who had positive antibody test results decreased from 2.85 (95% CI, 2.73-2.97) at 0 to 30 days to 0.67 (95% CI, 0.6-0.74) at 31 to 60 days, 0.29 (95% CI, 0.24-0.35) at 61 to 90 days, and 0.10 (95% CI, 0.05-0.19) after more than 90 days of the initial test.

In an editor’s note published alongside the study, Mitchell H. Katz, MD, wrote that the findings are consistent with previous research among health care workers who received antibody testing, but these studies cannot determine how long antibody protection stemming from a natural infection will last. This, he said, is why COVID-19 vaccination is recommended regardless of whether a person has antibodies.

“How long the antibody protection provided by vaccines will last is also unknown,” Katz wrote. “To know how long protection will last with antibodies because of natural infection or vaccination is something only time will tell.”

References:

Harvey RA, et al. JAMA Intern Med. 2021;doi:10.1001/jamainternmed.2021.0366.
Katz M, et al. JAMA Int Med. 2021;doi:10.1001/jamainternmed.2021.0374.