In a new study published in Nature’s Scientific Reports, a group of Canadian chemists led by the Université de Montréal examined the lab samples of patients who had recovered from a mild case of COVID-19.
The goal was to determine whether natural infection or vaccination resulted in the generation of more protective antibodies. When someone who has had a mild case is vaccinated, the antibody level in their blood doubles compared to someone who was infected and is unvaccinated.
Thirty-two SARS-CoV-2-positive and non-hospitalized Canadian adults were enrolled in the study two to three weeks post-diagnosis in 2020 prior to the emergence of the beta, delta and gamma variants.
Blood serum was collected from the patients four and 16 weeks after diagnosis and the participants were divided into four age-based cohorts.
Antibody levels were measured with variant spike proteins and the group reported a “sustained humoral response” against the variant spike proteins among the non-hospitalized Canadian adults.
Additionally, the response hindered the interaction between the variant spike proteins and the ACE-2 receptor – which acts as a receptor for the virus – for greater than 16 weeks post-diagnosis, with the exception of individuals aged 18-49 years old who showed no inhibition of the interaction between the receptor protein and the variant spikes.
The relationship measured between the variant spike proteins and antibodies from the serum of those who had been infected and vaccinated remained unchanged.
While antibodies produced by the native strain of the virus also reacted to variants, they did so to a lesser extent.
“On average, individuals in the 70 + years group exhibited ELISA and SPR responses 15% (native) to 30% (VOCs [variants of concern]) above the mean of the overall cohort, those aged 50–59 or 60–69 years exhibited responses within 10% of the mean, and those aged 18–49 years exhibited responses 18% (native) to 30% (VOCs) below the mean,” the authors wrote.
Surface plasmon resonance, or SPR, is a sensing technique used to conduct serological tests and measure biochemical parameters influencing humoral response that provides biochemical data to enzyme-linked immunosorbent assay (ELISA), a technique used to detect antigens.
Lastly, the serum from vaccinated individuals who received either the Pfizer/BioNTech or AstraZeneca vaccine was found to have higher antibody levels and more efficiently hinder the variant spike and ACE-2 receptor protein interactions – even among individuals aged 18–49 years old – which the scientists wrote showed the effectiveness of vaccination.
“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,” Joelle Pelletier, who led the research team, said in a statement.
“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,” she added. “We didn’t observe the same phenomenon with the other variants.”