In a new study from Sheba Medical Center, researchers found that although over time the number of SARS-CoV-2 antibodies falls in both previously infected and vaccinated patients, the performance of antibodies improves only after previous infection (and not vaccination).
This difference could explain why previously infected patients are better protected against a new infection than those who have only been vaccinated.
The team 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.
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.
In the study, the team analyzed the antibody-induced immune response in COVID-19 recovered but unvaccinated people 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 researchers followed up on 130 patients diagnosed with SARS-COV-2 using PCR testing.
They also tested 402 individuals who were double-vaccinated with the Pfizer vaccine but who had never had COVID-19.
The researchers found that the numbers of antibodies a month after vaccination were higher than those in the COVID-19 recovered patients. However, these numbers also declined more steeply in the vaccinated group.
The avidity (antibody performance quality) index was higher in vaccinated individuals than in recovered patients initially.
However, up to six months avidity did not strongly change in vaccinated individuals, whereas it gradually increased in recovered patients and potentially protected them from reinfection.
The team also found people with obesity who had been previously infected were better protected against future infection than those who were overweight or normal weight and had been previously infected.
They say while the number of antibodies decreases 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.
People with obesity have a much higher and sustained antibody-induced immune response following infection.
These results may explain the differential protection against COVID-19 in previously infected compared with only-vaccinated individuals.
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The study was presented at the European Congress of Clinical Microbiology & Infectious Diseases and was conducted by Dr. Carmit Cohen et al.
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