Previous Covid-19 Infection Rather Than Vaccination Improves Performance Of Antibodies

Covid no longer a Global Threat

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 rather than vaccination, according to a new study.

The new research is to be presented at this year’s European Congress of Clinical Microbiology & Infectious Diseases (ECCMID 2022, Lisbon, 23-26 April). The study, by Dr Carmit Cohen of the Sheba Medical Center, Ramat Gan, Israel, and colleagues, also found that previously infected patients with obesity had a higher and more sustained immune response than overweight and normal weight range patients.


The researchers note that protection against re-infection lasts for a long time in SARS-CoV-2 recovered patients. However, breakthrough infections are increasingly common six months after vaccination, they added. The authors in the study 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. Those previously infected in this study had been infected by the original and alpha variants (and some cases of beta) of SARS-CoV-2, although it is not known which variant for each patient as the laboratory only gained the ability to sequence variants long after the study began.


The researchers followed-up of 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 were reinfected across the study period. Data were collected on acute (during infection and immediately after) as well as long term (after 6 weeks) symptoms. They compared anti-spike protein IgG and neutralising antibodies of these 130 recovered patients to 402 age and body mass index (BMI), matched individuals who were double-vaccinated with the Pfizer vaccine but who had never had COVID-19. These double-vaccinated patients also remained uninfected across the study period; however, evidence had begun to emerge in Israel at this time (the second quarter of 2021) that double vaccinated, never infected healthcare workers were experiencing breakthrough’ infections at around six months after their second dose, whereas previously infected individuals that had not been vaccinated were not being reinfected.


Further, the researchers found 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 significantly change in vaccinated individuals, whereas it gradually increased in recovered patients and potentially protected them from reinfection.

Among the all recovered patients, the study notes down that 42 (36%) experienced long COVID symptoms including mental health (5%), neurological (9%), cardiovascular (5%) and respiratory (31%) manifestations.

This team of researchers is now following a cohort of people recovered from the delta variant (specifically focused on families) and also a separate cohort recovered from the omicron variant. In these newer studies, they are examining both the humoral and innate immune responses (different parts of the immue system). This team of researchers is now following a cohort of people recovered from the delta variant (specifically focused on families) and also a separate cohort recovered from the omicron variant.


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