Definition of the protection threshold against SARS-CoV-2 infection is essential for future vaccines and therapeutic strategies. A study from Toulouse University Hospital established a relationship between antibody concentration and protection against infection or reinfection. It also highlights that natural infection alone is much less protective than vaccination. In fact, it would only protect 12.4% to 79% of non-vaccinated infected people who were followed.
Published in the scientific journal on September 21, 2021 “journal of infection» The study, conducted by the Departments of Virology, Occupational Health and Infectious Diseases, was conducted on a group of hospital workers.
Safety less than 140 units / ml, 1700 units / ml . full protection above
This study is based on SARS-CoV-2 serology conducted from June 2020 to July 2021 with 8,758 caregivers, of whom 276 (3%) were seropositive as part of the initial screening.
The aim was to establish the relationship between the concentration of neutralizing antibodies and the total antibodies measured (by an enzyme immunoassay) and protection against infection or reinfection by SARS-CoV-2.
Based on 365 days of follow-up, the researchers obtained:
– 76.8% safety with a detectable neutralizing antibody titre strictly less than 64;
– 94% protection with a neutralizing antibody titre equal to 64 or 128;
– 100% protection with a neutralizing antibody titre greater than or equal to 256;
– 12.4% safety with total antibody concentration greater than 13 and less than 141 units/mL;
– 89.3% safety with total antibody concentration between 141 and 1700 units/mL;
– 100% protection with a total antibody concentration greater than or equal to 1700 units/mL.
Vaccination alone provides better protection against natural infection
These thresholds made it possible to evaluate natural infection alone (not after vaccination) and the protection provided by vaccination. After two doses of vaccines, 15 days after their second dose, none of the individuals had low concentrations of total antibodies, so they were all safe at 89.3%. In contrast, 79.3% of those previously infected but not vaccinated had a total antibody concentration less than 141 units/mL and had a level of protection against re-infection of only 12.4%.
Chloe DiMeglio, Biostatistician at the Virology Laboratory of the University Hospital of Toulouse, Prof. directed by Jacques Isopet : «The definition of these protection thresholds in relation to antibody response following vaccination or natural infection is needed today to refine vaccine protocols (third dose) or therapeutics (use of monoclonal antibodies), particularly for those who have not been exposed to classic vaccination. giving bad feedback. Schedules.»