Association of SARS-CoV-2 Seropositive Antibody Test With Risk of Future Infection

As we transition from an active phase of the COVID-19 pandemic to an active phase of vaccination, our attention is appropriately focused on immunity. During the former, our immunity is acquired through infection and recovery; in the latter, we hope for immunity based on response to an ever-growing array of vaccines. Two nagging questions that often surface are aimed at the level of protection and the durability of protection. If I have been infected, am I protected, and how long does my adaptive immunity last? Likewise, if I am vaccinated, for how long will I be protected? (Fortunately, we already know that there is impressive initial protection from the phase III clinical trials.)

The questions emerging from prior infection are addressed by a large, retrospective cohort study that evaluated over 3 million unique patients who had an initial SARS-CoV-2 antibody (Ab) test.¹ By coupling de-identified data across a commercial laboratory, medical and pharmacy claims, electronic health records, and hospitals, the research team identified patients who were subsequently assessed for SARS-CoV-2 using nucleic acid amplification testing (NAAT). A total of four time windows were utilized, including 0–30, 31–60, 61–90, and >90 days.

The majority (88.3%) of patients in this cohort had a negative Ab test at the onset; 11.7% had evidence of prior SARS-CoV-2 infection. The NAAT positivity of the Ab-negative group was relatively stable, at about 3%, across the four time periods, indicating a stable rate of acquiring infection. In contrast, the Ab-positive group demonstrated a steady decline in NAAT-positivity. Initially, the Ab-positive group had higher rates of NAAT-positivity, likely due to the prolonged shedding of viral RNA. The ratio of NAAT-positivity between the Ab-positive and Ab-negative groups declined from 2.85 at 0–30 days to 0.10 at >90 days. In other words, after 90 days, those patients who were initially Ab-negative had a 10-fold higher level of NAAT-positivity than patients who were Ab-positive. 

This study helps us understand the short-term dynamics of protection. At >90 days from initial detection of SARS-CoV-2–specific antibody, the relative protection from adaptive immunity from infection appears to be quite good. If infected and recovered, we are likely to be protected over the 3 subsequent months. We still do not know about persistence over a longer time frame, but this is a good start. Additional studies are needed to extend the time frame and address the important question of durability of vaccine-induced immunity.

Reference

1. Harvey RA, Rassen JA, Kabelac CA, et al. Association of SARS-CoV-2 seropositive antibody test with risk of future infection. JAMA Intern Med. 2021 Feb 24. doi: 10.1001/jamainternmed.2021.0366. Online ahead of print. https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2776810