Over 50s Produce Higher SARS-CoV-2 Antibody Levels After Prior Infection Than Younger Adults

Antibody proteins attacking coronavirus, illustration
Immunoglobulin, or antibody proteins, attacking a coronavirus, 3d illustration.

In a study published today in Scientific Reports, researchers in Canada observed that those who received the Pfizer BioNTech or AstraZeneca vaccine have antibody levels significantly higher than those of individuals who have been previously infected. These antibodies were also effective against the Delta variant, which wasn’t present in Quebec when the samples were collected in 2020.

The research team was led by Joelle Pelletier and Jean-François Masson, both professors in Université de Montréal’s Department of Chemistry. They wanted to find out whether natural infection or vaccination led to generation of more protective antibodies. In particular, they were interested in an understudied group: people who have been infected by SARS-CoV-2 but were not hospitalized as a result of the infection.

This study looked at 32 non-hospitalized, COVID-19 positive Canadian adults who were recruited by the Centre Hospitalier de l’Université Laval 14 to 21 days after being diagnosed through PCR testing. This was in 2020, before the Beta, Delta and Gamma variants emerged.  Sera were collected 4 and 16 weeks post-diagnosis. Antibody levels and pseudo-neutralization of the ectodomain of SARS-CoV-2 spike protein/human ACE-2 receptor interaction were analyzed with native, B.1.351, B.1.617.2 and P.1 variant spike proteins.

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

Antibodies produced after an infection by the original, “native” strain of the virus also reacted to SARS-CoV-2 variants that emerged in subsequent waves, namely Beta (South Africa), Delta (India) and Gamma (Brazil), but to a lesser extent: a reduction of 30 to 50 percent.

“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, ” said Pelletier.

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

When someone who has had a mild case of COVID is vaccinated, the antibody level in their blood doubles compared to an unvaccinated person who has been infected by the virus. Their antibodies are also better able to prevent spike-ACE-2 interaction.

“But what’s even more interesting,” said Masson, “is that we have samples from an individual younger than 49 whose infection didn’t produce antibodies inhibiting spike-ACE-2 interaction, unlike vaccination. This suggests that vaccination increases protection against the Delta variant among people previously infected by the native strain.”

The study was done in collaboration with Université Laval, the Centre hospitalier de l’Université Laval, Héma-Québec and the National Research Council of Canada. It was funded by the Canadian Institutes of Health Research, the Natural Sciences and Engineering Research Council of Canada, the National Research Council of Canada’s Pandemic Response Challenge Program and the Canada Foundation for Innovation.

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