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NEW YORK, NEW YORK – SEPTEMBER 15: People in masks carry groceries as they cross the street as … [+]
There is a question that has gone through all of our minds at some point, but it does not have a satisfactory answer: if I am infected with SARS-CoV-2, the virus that causes Covid-19, how long am I immune? A more technical way of asking the same question is: How long do anti-SARS-CoV-2 antibodies that bind to the spike protein persist?
While a new study on anti-SARS-CoV-2 antibodies, published yesterday in JAMA, doesn’t have much to offer in terms of definitive answers, it does provide a disturbing perspective on our natural immunity, or lack thereof, to Covid. 19. Complemented by recent reports of reinfection, this study and others like it give us much to think about when it comes to how we are progressing in our response to the pandemic.
By taking samples from healthcare personnel who work directly with Covid-19 patients at Vanderbilt University Medical Center in Nashville, Tennessee, researchers found that 58 percent of those who tested positive for anti-SARS antibodies- CoV-2 in April tested negative only two months later. His antibody levels had dropped so precipitously that they were no longer detectable. Even the 42 percent of staff whose antibody levels remained above the threshold still experienced a significant decline (see Figure 1).
FIGURE 1: Tracking graph of the decrease in antibody levels. Each line represents one patient.
The researchers’ assay targets, in other words, the specific antibodies they were measuring, were anti-SARS-CoV-2 antibodies raised against the viral spike protein. Previous research suggests that these antibodies are critical to the body’s ability to neutralize the virus in patients with mild or severe illnesses. It is not certain if their disappearance leaves the body totally unprotected, but it raises the question of what immune mechanisms protect us if these antibodies cannot.
We ask this question knowing, thanks to two scientific case studies published last month on Covid-19 patients in Hong Kong and the United States, respectively, that it is possible to be re-infected with Covid-19 within a few months of first having it. While the United States case study, which focuses on a 25-year-old man in Nevada, is still being peer-reviewed, it is in our collective interest to take these reports very seriously.
Reinfection is something of a signature move in the coronavirus family, and documentation of this ability dates back to the late 1970s and 1980s. If SARS-CoV-2 is more lethal and more transmissible than its seasonal cold-causing cousins, it would be naive to assume that it wouldn’t be more adept at putting together its oldest, dirtiest stunt as well. A six-year study of the human coronavirus NL63 (HCoV-NL63), published in 2018, found that people who had contracted the virus in homes and hospitals on the Kenyan coast were sometimes infected not just once or twice, but three times. .
The authors of the Kenyan study speculate that the antibodies may have enhanced the infection, rather than prevented it, commenting that this was found to have occurred with SARS-CoV, the virus that caused the first deadly coronavirus pandemic. Such a possibility further complicates our understanding of the role of anti-SARS-CoV-2 antibodies and our immunity to coronaviruses in general. Even its tendency to be short-lived is not a fact. A recent Icelandic study of population antibody levels found that about 91 percent of participants who tested positive for Covid-19 retained anti-SARS-CoV-2 antibodies two months after their initial diagnosis.
The reasons such inconsistencies persist remain elusive, but their implications for how we control and contain Covid-19 are ultimately the same. We cannot rely on natural immunity to protect us from this virus. As long as we don’t have a vaccine, we must use evidence-based testing, assisted isolation, and other public health measures to build effective and long-lasting defenses. The stakes are too high for us to sit back and wait.
