Vaccinated people have a higher level of antibodies than those who develop antibodies after catching COVID, and those who have recovered and then been vaccinated have an even higher level.

Scientists from the University of Montreal have found that in people who have had a mild COVID-19, after vaccination, the level of antibodies doubles. 

In addition, it was found that many elderly people who underwent COVID-19 at the beginning of the pandemic still retain immunity, which protects well against even the Delta strain.  

Since most of the studies are devoted to assessing the level of antibodies in vaccinated and recovered from COVID-19 in moderate and severe forms, Canadian experts have focused on comparing the immune protection in three groups: those who have recovered after the mild or asymptomatic form, vaccinated and recovered, and then vaccinated. 

It is noted that the study began in 2020. At the Centre hospitalier de l’Université Laval, scientists examined 32 Canadian adults who had been diagnosed with a mild coronavirus two to three weeks ago. 

Then, over the course of a year, they observed changes in the level of antibodies as new strains of coronavirus appeared. 

During this time, some patients were vaccinated. The data were compared with a control group of non-COVID-19 patients. 

The results showed that those vaccinated with Pfizer BioNTech or AstraZeneca had significantly higher antibody levels than those infected, and among those who had recovered, high titers persisted longer in the elderly. 

“Everyone who had been infected produced antibodies, but older people produced more than adults under 50 years of age. In addition, antibodies were still present in their bloodstream 16 weeks after their diagnosis,” said one of the study leaders.

“But the result that surprised us the most was that antibodies produced by naturally infected individuals 50 and older provided a greater degree of protection than adults below 50,” added the study authors.

“This was determined by measuring the antibodies’ capacity to inhibit the interaction of the Delta variant’s spike protein with the ACE-2 receptor in human cells, which is how we become infected,” they added.

“We didn’t observe the same phenomenon with the other variants.”

Université Laval, the Centre hospitalier de l’Université Laval, Héma-Québec, and the National Research Council of Canada collaborated in the research. The Canadian Institutes of Health Research, the Natural Sciences and Engineering Research Council of Canada, the Pandemic Response Challenge Program of the National Research Council of Canada, and the Canada Foundation for Innovation also contributed to the project.

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