Respiratory syncytial virus (RSV) is the leading cause of hospitalization in young infants in Canada. While most babies recover, RSV can cause severe breathing problems and place major stress on families and the health system. Infants born to pregnant women and people with HIV, even if they do not acquire the virus, face higher risks of RSV illness. This is partly because HIV increases the chance of preterm birth and can reduce the amount of protective antibodies passed to the baby during pregnancy.

Two new tools now exist to prevent RSV. One is a vaccine given in late pregnancy (RSVpreF), which boosts antibodies that cross the placenta and protect the baby at birth. The other is a long-lasting antibody (nirsevimab) given directly to infants after delivery. Both work well in the general population, but pregnant people living with HIV were excluded from the original studies. Health care providers therefore do not know if perinatal vaccination provides enough protection for these babies.

This study will follow 20 pregnant women/people with HIV at BC Women's Hospital who receive the RSVpreF vaccine. Antibody levels will be measured before and after vaccination from the pregnant recipient, and in infant blood sample, to see how well protection is transferred to infants. We will also assess vaccine safety, birth outcomes, and parental views on RSV immunization. Findings will guide Canadian policies to ensure that all infants, including those exposed to HIV, have equitable access to RSV protection.

Inclusion Criteria:

1. Pregnant women/people aged ≥19 years
2. Confirmed diagnosis of HIV
3. Gestational age between 28 and 34 weeks at enrollment (to allow scheduling of vaccination at 32-36 weeks)
4. Able to provide informed consent

Exclusion Criteria:

1. Contraindications to RSVpreF vaccine per product monograph
2. History of severe allergic reaction to any vaccine component
3. Planned delivery outside of British Columbia
4. Received RSVpreF in current or previous pregnancy
5. Received immunoglobulins (except Rh (D) immuneglobulin) within 1 year of enrollment
6. Unable to complete in-person follow-up for infant at the Oak Tree Clinic