Group B strep vaccine in pregnancy worked as well with HIV as without

Design

double-blind, randomised, placebo-controlled phase 2 trial, stratified by maternal HIV status, followed to 12 months post-delivery

Population

300 pregnant women aged 18-40 in Kampala, Uganda (150 living with HIV, 150 without), 27+0 to 35+6 weeks, low-risk singleton pregnancy

Primary outcome

maternal and infant safety after vaccination

Effect

no significant difference in antibody response by HIV status for any serotype (e.g. Ia 12.02 vs 9.38, p=0.575); no serious adverse event attributed to the vaccine

A double-blind placebo-controlled phase 2 trial at five antenatal facilities in Kampala randomised 300 pregnant women — half living with HIV, half not — to 20 µg of the hexavalent group B streptococcus conjugate vaccine GBS6 or saline, given between 27 and 36 weeks. Mother-infant pairs were followed to 12 months after delivery.

Antibody responses at one month showed no significant difference by HIV status for any of the six serotypes: for example, serotype Ia geometric mean concentration 12.02 in women living with HIV against 9.38 in women without (p = 0.575), serotype III 4.38 against 5.64 (p = 0.469). Antibody declined over the year but stayed above placebo at 12 months, and HIV-exposed infants responded like unexposed ones. Solicited reactions were mild to moderate. Of 86 serious adverse events, none was attributed to the vaccine; stillbirths were 1 of 74 among vaccinated women living with HIV against 3 of 76 among those given placebo.

Maternal immunisation programmes routinely have to answer the question this trial was built for: does the vaccine still work in women whose immune systems are compromised, and is it safe in them. For group B streptococcus — a leading cause of early neonatal sepsis in settings with no intrapartum prophylaxis — the answer here is that HIV status did not change either. That is the finding that lets a future programme be universal rather than stratified.

• This is immunogenicity and safety, not protection — no efficacy endpoint was measured
• Serotype V responses were low in both groups, which matters for a hexavalent formulation
• Where intrapartum antibiotic prophylaxis is not feasible, maternal vaccination is the realistic route to preventing early-onset disease
• Indian data on group B streptococcus colonisation and early-onset sepsis remain patchy; do not assume the Ugandan serotype distribution applies

Why it matters

It removes the main uncertainty blocking maternal group B strep vaccination in the settings with the highest neonatal sepsis burden.

Don't overread it

Phase 2, 300 women, antibody endpoints — this does not show that infant disease is prevented.

The statistics, in plain English

Geometric mean concentrations are used because antibody titres are skewed; comparing them with p values, as here, asks only whether a difference was detected, not whether the levels protect. No protective threshold is established for group B streptococcus antibody, so a higher number is not yet a promise. With 300 women, small differences in safety events cannot be ruled out.

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