A 3rd Dose of the COVID-19 Vaccine Could be Required for Certain Immunocompromised Individuals


Montreal, August 14, 2021 – While vaccine booster campaigns are being planned in certain countries around the world for at-risk populations, researchers at the University of Montreal Hospital Research Centre (CRCHUM) have measured humoral responses elicited by the COVID-19 vaccine in people living with HIV. In an article published on the pre-print server bioRxiv, the research team headed by Dr. Cécile Tremblay and Andrés Finzi present preliminary results indicating that immunocompromised people respond variably to the vaccine depending on their level of CD4+ T cells.

Messenger RNA vaccines have proven to be extremely effective in protecting against severe forms of the disease, hospitalizations and deaths. Even though these vaccines continue to be effective against emerging variants, including Delta, a higher level of antibodies is needed to provide optimal protection. Many studies have assessed vaccine responses in immunocompromised patients, mostly in transplant patients or patients with auto-immune disease, cancer, or on dialysis, but fewer studies have measured the reaction of HIV-positive individuals.

“We have known for a long time that people living with HIV have weaker responses to certain types of vaccines and that the responses depend on the number of CD4+ T cells. These cells have a significant impact on the production of antibodies and play an essential role in the immune response. In the context of the emergence of more resistant variants, we wanted to measure whether this category of the population had an adequate response to vaccination,” explained Dr. Cécile Tremblay, a microbiologist and infectious disease specialist and researcher at the CRCHUM.

About a hundred HIV-positive people were recruited for this study and their immunogenicity was measured 4 weeks after receiving a first dose of the Moderna vaccine.

“Looking at the overall results, the response to the vaccine is similar to that of the general population. However, when we stratify by CD4 T cell counts, we noticed a weaker response in the group of individuals with a low level of CD4+ T cells. If the trend continues after the second dose, these data would support the hypothesis that a booster dose might be required for this population,” indicated Andrés Finzi, a researcher at the CRCHUM and Université de Montréal professor.

While other studies found no association between age and immune response to the vaccine in this population, the research team’s data hints at a correlation after a single dose. The test group will be followed over a period of one year to evaluate the durability and quality of these responses.

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About the CRCHUM

The University of Montreal Hospital Research Centre (CRCHUM) is one of North America’s leading hospital research centres. It strives to improve adult health through a research continuum covering such disciplines as the fundamental sciences, clinical research and public health. Over 1,850 people work at the CRCHUM, including more than 550 researchers and more than 460 graduate students.

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SOURCE: Centre hospitalier de l'Université de Montréal (CHUM)

For further information:
Andrée-Anne Toussaint, communications advisor, media relations
514-890-8000, ext. 23675
andree-anne.toussaint.chum@ssss.gouv.qc.ca