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Over 60,000 people in Canada are living with HIV.  Numerous studies early in the COVID-19 pandemic indicated that people living with HIV (PLWH) may be at risk of more severe outcomes and COVID-19 vaccination was therefore strongly recommended in this group.  However, there is evidence that HIV infection can reduce vaccine-induced immune responses and it was not clear whether this may also be the case for COVID-19 vaccines.  Therefore, this project aimed to examine the immune responses to COVID-19 vaccination in PLWH and to identify other factors (such as socio-demographic or clinical factors) which may affect immune responses, to inform public health decision-making.

Samples were taken from study participants before their first vaccination and then after their first, second and third doses. Their immune responses were analyzed using these samples.  The team found that after two vaccine doses, HIV status did not significantly impact the level of immune response. Rather, older age, chronic health conditions, and having received two AstraZeneca vaccine doses (as opposed to mRNA vaccinations) were associated with lower responses after two vaccine doses.

As expected, it was observed that immunity naturally declined over time in all participants (regardless of HIV status), and that a third vaccine dose boosted antibody responses to levels higher than after two doses.  The study also found that vaccination offered less protection against Omicron than against the original variant, even after three doses, providing strong evidence for the use of bivalent boosters, which target Omicron as well as the original variant.  Data was shared with public health authorities, community groups and the general public throughout the study, and work is ongoing to follow up with participants after their fourth dose.