The older you are, the more antibodies you have: Study

With the emergence of SARS-CoV-2 variants worldwide, the pandemic's spread is accelerating. A research team led by Joelle Pelletier and Jean-Francois Masson, both professors in Universite de Montreal's Department of Chemistry, wanted to find out whether natural infection or vaccination led to more protective antibodies being generated.

In their study published in Scientific Reports, they observe that those who received the Pfizer BioNTech or AstraZeneca vaccine had antibody levels that were significantly higher than infected individuals. These antibodies were also effective against the Delta variant, which wasn't present in Quebec when the samples were collected in 2020.

Masson, a biomedical instruments specialist, and Pelletier, a protein chemistry expert, 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.

Consequently, 32 non-hospitalized COVID-19 positive Canadian adults were recruited by the Centre Hospitalier de l'Universite Laval 14 to 21 days after being diagnosed through PCR testing. This was in 2020, before the Beta, Delta, and Gamma variants emerged.

"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 Masson.

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 per cent.

"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. We didn't observe the same phenomenon with the other variants," he added.

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, 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," said Masson.

Both scientists believe more research should be conducted to determine the best combination for maintaining the most effective level of antibodies reactive to all variants of the virus.