This is a summary, written by members of the CITF Secretariat, of:

Matveev VA, Mihelic EZ, Benko E, Budylowski P, Grocott S, Lee T, Korosec CS, Colwill K, Stephenson H, Law R, Ward LA, Sheikh-Mohamed S, Mailhot G, Delgado-Brand M, Pasculescu A, Wang JH, Qi F, Tursun T, Kardava L, Chau S, Samaan P, Imran A, Copertino Jr DC, Chao G, Choi Y, Reinhard RJ, Kaul R,  Heffernan JM, Jones RB,  Chun TW, Moir S, Singer J, Gommerman J, Gingras AC, Kovacs C, Ostrowski M. Immunogenicity of COVID-19 vaccines and their effect on the HIV reservoir in older people with HIV. bioRxiv 2023.06.14.544834; doi:

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

A CITF-funded study, published in preprint and not yet peer-reviewed, found older people living with HIV require at least three doses of COVID-19 vaccines to maximize immune responses against SARS-CoV-2. Vaccines, however, may increase HIV reservoirs in people with HIV who have low-level persistent viremia. The study was led by Dr. Mario Ostrowski (University of Toronto) in collaboration with other CITF-funded researchers Drs. Anne-Claude Gingras (Lunenfeld-Tanenbaum Research Institute, Sinai Health), Jennifer Gommerman (University of Toronto), and Jane Heffernan (York University).

68 people living with HIV (PLWH) aged 55 and older and 23 age-matched HIV-negative individuals were followed for 48 weeks from the first vaccine dose, after a total of three doses. All PLWH were on antiretroviral therapy but their immune status differed and included immune responders (IR)HIV-infected individuals in whom the administration of antiretroviral therapy is successful in suppressing viral replication and fully reconstituting patient circulating CD4+ T-cell numbers to immunocompetent levels., immune non-responders (INR)HIV-infected individuals in whom the administration of antiretroviral therapy, although successful in suppressing viral replication, does not fully reconstitute patient circulating CD4+ T-cell numbers to immunocompetent levels., and people with low-level viremia (LLV)People living with HIV with a persistent viral load of 50-200 copies/ml, even after receiving antiretroviral therapy. This has been linked to inferior treatment outcomes..

Key findings:

  • Various regimens of Pfizer, Moderna, and AstraZeneca vaccines elicited equally strong anti-spike IgG responses in serum and saliva among PLWH and HIV-negative participants at all time points.
  • Antibody responses peaked at four weeks after the third dose in both cohorts. The half-lifeThe length of time required for the concentration of a particular substance (in this case, antibodies) to decrease to half of its starting dose in the body. of IgG antibodies increased after the third dose in both groups.
  • Salivary spike IgA responses were modest in PLWH relative to the HIV-negative participants. Weaker spike IgA responses were observed in INRs, compared to IRs but the differences were not statistically significant.
  • PLHW had markedly lower live virus-neutralizing titers after two vaccine doses when compared with HIV-negative participants. The live virus-neutralizing titers in PLWH were similar to those in HIV-negative controls after a booster.
  • Most breakthrough infections occurred after the third vaccine dose, however this was during the spread of Omicron. Breakthrough infections were less frequent among PLWH than in HIV-negative participants.
  • Anti-spike T-cell immunity was enhanced in IRs, even in comparison to HIV-negative participants, while in INRs it was the lowest.
  • Anti-spike B-cell immunity was enhanced after the third vaccine dose in both PLWH and HIV-negative participants.
  • Increased frequency of viral blips – a temporary spike in the viral load – in PLWH was seen post-vaccination. However, vaccines did not affect the size of the intact HIV reservoir in CD4+ T cells in most PLWH, except in LLVs.

Overall, the study suggested that despite suboptimal initial immune responses in PLWH, the third doses seemed to have rescued their immune responses, rendering them similar to those of HIV-negative individuals.