According to a new study, although over time the number of SARS-CoV-2 antibodies falls in both previously infected and vaccinated patients, the performance of antibodies improve only after the previous infection.

The researchers, including Carmit Cohen of the Sheba Medical Center, indicated that while protection against re-infection lasts for a long time in SARS-CoV-2 recovered patients, breakthrough infections are increasingly common six months after vaccination. "While the number of antibodies decrease with time in both COVID-19 recovered (but never vaccinated) patients and vaccinated (but never infected) individuals, the quality of antibodies increases the following infection but not after vaccination," the researchers said.

The study also found that, contrary to expectations, previously infected patients with obesity had a higher and more sustained immune response than overweight and normal weight range patients. For the study, to be presented at this year's European Congress of Clinical Microbiology and Infectious Diseases, the team analysed the humoral (antibody-induced) immune response in COVID-19 recovered but unvaccinated individuals for up to a year and compared it with those who had received two doses of the Pfizer vaccine (but no previous infection) over eight months.

The study recruited previously infected-unvaccinated and double vaccinated never infected individuals from March 25 to November 25 2020 and closed in April 2021, just before the Delta variant arrived in Israel. The researchers followed up on 130 patients diagnosed with SARS-COV-2 using PCR testing. These patients had not been vaccinated and remained unvaccinated during the study. None of these patients was reinfected during the study period.