A new study directed by Dr. Hélène Decaluwe of CHU Sainte-Justine suggests that a mixed approach, combining intramuscular and mucosal vaccine administration techniques, could be an effective avenue for preventing serious SARS-CoV-2 infections and reducing the transmission of COVID-19. The study was conducted in close collaboration with the Dr. Jennifer Gommerman’s team, at the University of Toronto, and with CoVaRR-Net, a Canadian consortium of researchers and experts who are studying worrisome variants of respiratory viruses, including COVID-19.

Vaccination: Intramuscular or intranasal?

One of the study’s most important discoveries is that the immune system’s stimulation pathway has a significant impact on the efficacy of the immune response. Dr. Decaluwe, who is also a clinical associate professor with the pediatric department of allergy, immunology and rheumatology at Université de Montréal, and her team found that for previously vaccinated people, infection by the Omicron variant through the nasal pathway triggered a more effective immune response than an intramuscular booster injection.

Since mucosal vaccinations tend to mimic natural infection, without the related infectious risk, the results of this new study suggest that a mucosal booster vaccination (intranasal, for example) could improve long-term protection against COVID-19 for vaccinated people.

Although intranasal vaccines against COVID-19 are not yet available in Canada and are undergoing further study, these results pave the way to new approaches to vaccination against COVID-19 for an optimal immune response.

Effects of booster vaccinations and natural immunity against COVID-19

The study, launched in 2021, focused on the period during which the Omicron variant emerged, when boosters were being introduced. The researchers examined the benefits of booster vaccinations and how they could help prevent hospitalization and deaths related to COVID-19. Their objective was to understand how the immune system reacts to COVID-19 and the differences in immune response in people who had been vaccinated, people who had been naturally infected and people who had been both infected with the virus and vaccinated.

For the study, the team recruited two groups of people: 52 who had been infected early during the pandemic (from a larger group of 569 healthcare workers in Montréal, as part of the RECOVER study, led by Caroline Quach-Thanh at CHU Sainte-Justine) and then vaccinated and 71 who had been vaccinated without previously having been infected (part of the CoVaRR-Net cohort). In these groups, the team identified people who had been infected by the Omicron variant and those who had received a booster vaccination. The researchers analyzed the immune response of each group, focusing on the antibodies produced and their capacity to neutralize the virus, as well as on the cellular immune memory response.

Optimal immunization strategies

The results of this study offer a ray of hope in the battle against COVID-19 by suggesting a combined intramuscular and intranasal vaccination approach to reinforce the immune response.

Although intranasal vaccines are not yet available, these discoveries pave the way for new strategies to increase long-term protection against the virus. This promising progress brings us a little closer to gaining control of the pandemic and establishing effective, lasting public health protection.