Preliminary data generated from a study funded by the Government of Canada through the COVID-19 Immunity Task Force (CITF) reveals subtle differences between the immune responses of long-term care residents receiving the Pfizer-BioNTech or Moderna vaccines. Nevertheless, having as many people vaccinated as possible may also reduce the risk of ongoing circulation of the virus and the emergence of future variants.

The research, which is in pre-print and therefore not yet peer-reviewed, was led by Lunenfeld-Tanenbaum Research Institute (LTRI) senior scientists Dr. Anne-Claude Gingras and Dr. Allison McGeer and reveals that long-term care (LTC) residents in Ontario who received the Pfizer vaccine had lower antibody responses to Alpha, Beta and Gamma than those vaccinated with the Moderna vaccine. The Delta variant was not assessed.

Anne-Claude Gingras

 Senior investigator Anne-Claude Gingras

“Our study does raise concerns about the response to vaccination in some residents of long-term care homes in Ontario who overall responded more weakly to vaccination,” says Dr. Gingras, who is also the Functional Genomics & Structure-Function of VOCs Pillar Lead for the Coronavirus Variants Rapid Response Network (CoVaRR-Net). “In this population, the Moderna vaccine permitted more residents to generate an antibody response capable of neutralizing several SARS-CoV-2 variants.”

These results demonstrate immunogenicity, or antibody responses, to inform policies for highly vulnerable population and COVID-19 vaccine strategies.

The study examined total and neutralizing antibodies produced before and after vaccination, comparing 198 LTC residents to 78 caregivers and LTC staff. All vaccines were given three to four weeks apart and samples were taken 14 to 28 days after the second dose of vaccine.

It showed that the differences between resident responses to the two vaccines were more common against variants of concern (VOCs): neutralizing antibodies against the Beta variant were undetectable in nearly 38 per cent of residents vaccinated with the Pfizer vaccine, compared to 11.5 per cent of residents vaccinated with the Moderna vaccine. When it came to the Gamma variant, 29 per cent of those vaccinated with Pfizer did not neutralize the variant, whereas only five per cent of those vaccinated with Moderna did not neutralize Gamma. It is unknown how these laboratory assays compare to real life protection.

Dr. Allison McGeer

 Senior clinician scientist Dr. Allison McGeer

The study also showed that caregivers and staff, with a median age of 47, produced more neutralizing antibodies compared to residents, whose median age was 89. This is consistent with what is known about immune responses and age.

“The first two waves of the pandemic had a devastating impact on LTC home residents, staff and families,” says McGeer. “As we may face a fourth wave of the pandemic, we need to be sure that we are using all the tools we have to ensure that we protect residents and staff from further harm. This includes considering whether a third vaccine dose should be offered to residents.”

The scientists note they only looked at one facet of the immune response — the production of antibodies — adding residents who do not mount strong neutralizing antibody responses may still be protected by other facets of their immune system, like their T cells. It is also not known what level of antibody is needed to protect against Infection, severe disease or hospitalization.

“These are valuable findings,” says Dr. Catherine Hankins, CITF Co-Chair. “The question of booster strategies for vulnerable people who may not mount as strong an immune response and who have had a suboptimal reaction to two doses of mRNA vaccines is drawing lots of attention and debate. The effect of the higher antigen dose in Moderna is clearly part of the puzzle. The CITF is currently organizing a meta-analysis of data from seven studies that we’ve supported in long-term care settings, and we expect to have additional insights in the near future.”