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The question of immunity to COVID-19 is on everyone’s lips. The answer could make or break hopes for vaccines and have a major impact on governments’ response to the pandemic.
Without a clear understanding of the nature and longevity of immunity acquired after infection with SARS-CoV-2, the feasibility of vaccines and the possibility of using them to achieve herd immunity, thus nullifying the threat of the virus, is unknown. . To solve this problem, a team of researchers from the University of Arizona Health Sciences (AZ, USA), led by Deepta Bhattacharya and Janko Nikolich-Zugich, studied the production of antibodies in almost 6000 people.
The study began with the development of a blood test for SARS-CoV-2 by Bhattacharya, Nikolich-Zugich, and their team. This test was developed to identify antibodies generated to attack two separate sites on the SARS-CoV-2 spike protein, S1 and S2, the first of these sites includes the receptor-binding domain and is the target of most tests. .
The test requires the presence of both antibodies to give a positive result. Trials for the trial began in April 2020 and involved 5,882 asymptomatic and afebrile volunteers. 61 people in the cohort were found to be seropositive for sites S1 and S2, with only one false positive result recorded. This level of precision led to the approval of the test by the FDA (MD, USA) in August.
Bhattacharya and Nikolich-Zugich then decided to track antibody levels in those deemed positive by their test over the course of several months. This revealed that antibodies to the virus are observed at levels capable of neutralizing the virus for at least 5 to 7 months.
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Exclaiming the importance of these findings, Michael D. Dake, co-author of the paper, stated that, “This research has not only provided us with the ability to perform accurate antibody tests against COVID-19, but has also armed us with the knowledge that durable immunity is a reality. “
Bhattacharya also emphasized that immunity could last longer than the 5-7 months described in this study. “The last time points that we tracked in infected people were the last seven months, so this is the longest period that we can confirm that immunity lasts,” he said.
“That said, we know that people who were infected with the first SARS coronavirus, which is the virus most similar to SARS-CoV-2, still have immunity 17 years after infection. If SARS-CoV-2 looks like the first one, we expect the antibodies to last at least 2 years, and something much shorter would be unlikely to happen. “
The authors explain that the difference in the results of this study highlights the fact that most studies on immunity to SARS-CoV-2 have extrapolated the decrease in antibody production after the initial infection to determine the duration of immunity.
However, there are two key stages of antibody-based immunity. The first involves the rapid production of antibodies from short-lived plasma cells. These cells are then gradually replaced by long-lived plasma cells that produce high-quality antibodies at a much lower rate and quantity. Extrapolating the long-term antibody decline using data from the first few weeks of infection therefore ignores the impact of long-lived plasma cells, which can provide misleading results.
Importantly, this study would need to contain a larger cohort of HIV-positive participants to be considered conclusive and until challenge trials begin in January, it will be difficult to be fully definitive on the question of immunity to COVID-19. But one thing is for sure, this study reinforces hopes for a positive impact of vaccines against the virus.
