COVID-19, one year on: persistence of protective antibodies and significantly reduced risk of reinfection

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A study conducted by the University Hospital of Strasbourg (HUS) in collaboration with the Institut Pasteur, published as a preprint on medRxiv, has led to a significant advance in knowledge about COVID-19.

In connection with the SeroCoV-HUS study led by Professor Samira Fafi-Kremer (University Hospital of Strasbourg (HUS) – University of Strasbourg – INSERM UMR1109), the team at Strasbourg Regional University Hospital, in collaboration with the Institut Pasteur, monitored 1,309 hospital staff – 393 who had had a mild form of SARS-CoV-2 and 916 who had not contracted the infection – for one year. The scientists demonstrated that in those who had tested positive for COVID-19, the antibodies directed against the virus spike protein (anti-S) fell more quickly in men than in women, but that they persisted in nearly everyone until 13 months after infection. After administration with a single vaccine dose, the rate of antibodies increased significantly, regardless of the pre-vaccine rate and the type of vaccine administered. A comparison of the two cohorts demonstrated that the incidence of reinfection was reduced by 96.7% in convalescent COVID-19 patients.

These results demonstrate the long-term persistence of anti-S antibodies, which can help protect against reinfection. A single-dose vaccination strengthens protection against variants by significantly increasing protective antibody titers. Evaluating the kinetics of anti-SARS-CoV-2 antibodies is vital in predicting levels of protection against reinfection and the durability of vaccine protection.

The team from Strasbourg University Hospital monitored 393 hospital staff who had contracted a mild form of COVID-19 up to 422 days after the onset of symptoms. From the first to the ninth month (M), anti-SARS-CoV-2 antibodies fell moderately, with a sharper fall in IgG anti-spike (anti-S) antibodies in men than in women. One year after infection, 97% of individuals still had anti-S antibodies, with a median titer of 2.3 log AU/mL, while just 20% still had anti-nucleocapsid antibodies (anti-N).

An analysis of 916 hospital staff over the same period revealed 69 new infections, 32 during the third wave, while only one case of asymptomatic reinfection was observed in the group previously infected with SARS-CoV-2. This indicates that the risk of reinfection was reduced by 96.7% in the individuals that had previously been infected.

In collaboration with the Institut Pasteur team, a live-virus neutralization assay was performed. This demonstrated that the initial virus and the so called “UK variant” (B.1.1.7, now termed variant Alpha, but not the “South African variant” (B.1.351) (or variant Beta), are sensitive to anti-S antibodies at 2.3 log AU/mL, while an antibody titer of ≥ 3 log AU/mL neutralizes all three variants. This antibody level was reached by all the vaccinated convalescent individuals, regardless of their pre-vaccine rate and the type of vaccine administered.

Better protection against variants

These results demonstrate the long-term persistence of anti-S antibody titers, which can protect convalescent COVID-19 patients against reinfection with the initial strain and the British variant. By increasing the level of neutralizing antibodies, the SARS-CoV-2 vaccine can strengthen their protective capacity, especially against variants with antibody escape mutations like the South African variant.

Future research will help determine whether vaccine-induced antibodies evolve in the same way and whether their kinetics vary between men and women.

The SeroCoV-HUS team would like to extend its sincere thanks to all the participants in the study and to all those who contributed in any way to making sure it ran smoothly.

"This large cohort study has provided crucial information for the first time about the persistence of antibodies against SARS-CoV-2 after a mild case of COVID-19 and the long-term risk of reinfection. The results also revealed a correlation between the levels of anti-S antibodies (measured with a commercial quantitative assay) and neutralizing antibodies (measured with a live-virus neutralization assay), which will be highly valuable in interpreting serological results and assessing the rate of protection in future. The research will make a significant contribution to our understanding of the natural history of COVID-19 and the evolution of the pandemic. We intend to extend the study so that we can monitor patients at 18 and 24 months and gain a more long-term overview of antibody dynamics," explains Professor Samira Fafi-Kremer, Head of the Virology Department at the University Hospital of Strasbourg.



Anti-SARS-CoV-2 Antibodies Persist for up to 13 Months and Reduce Risk of Reinfection, MedRxiv, 17 mai 2021

Floriane Gallais1,2, Pierre Gantner1,2 Timothée Bruel3,4,5, Aurelie Velay1,2, Delphine Planas3,4,5, Marie-Josée Wendling1, Sophie Bayer6, Morgane Solis1,2, Elodie Laugel1,2, Nathalie Reix6, Anne Schneider7, Ludovic Glady6, Baptiste Panaget1,2, Nicolas Collongues8, Marialuisa Partisani9, Jean-Marc Lessinger6, Arnaud Fontanet10,11, David Rey9, Yves Hansmann12, Laurence Kling-Pillitteri13, Olivier Schwartz3,4,5, Jérome De Sèze8, Nicolas Meyer14, Maria Gonzalez12, Catherine Schmidt-Mutter8, Samira Fafi-Kremer1,2

1 Virology Laboratory, Strasbourg University Hospital, Strasbourg, France;
2 Strasbourg University, INSERM, IRM UMR-S 1109, F-67000 Strasbourg, France;
3 Virus & Immunity Unit, Department of Virology, Institut Pasteur, Paris, France;
4 CNRS UMR 3569, Paris, France;
5 Vaccine Research Institute, Creteil, France;
6 CHU de Strasbourg, Laboratoire de Biochimie Clinique et Biologie Moléculaire, F-67091 Strasbourg, France;
7 CHU de Strasbourg, Département de Génétique Moléculaire du cancer, F-67091 Strasbourg, France;
8 Centre d'investigation Clinique INSERM 1434, CHU Strasbourg, France;
9 CHU de Strasbourg, Trait d’Union, F-67091 Strasbourg, France;
10 Emerging Diseases Epidemiology Unit, Department of Global Health, Institut Pasteur, Paris, France;
11 PACRI Unit, Conservatoire National des Arts et Métiers, Paris, France ;
12 CHU de Strasbourg, Service des infectieuses et tropicales, F-67091 Strasbourg, France;
13 CHU de Strasbourg, Service de Pathologies Professionnelles, F-67091Strasbourg, France;
14 CHU de Strasbourg, Service de santé Publique, GMRC, F-67091 Strasbourg, France

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