Phase 3 trial of Ad5-nCoV vaccine shows no increased short-term HIV infection risk in 44,247 participants.

This Phase 3 randomized controlled trial was conducted across 66 clinical sites in Argentina, Chile, Mexico, Russia, and Pakistan. The study population comprised 44,247 participants who were HIV-negative at baseline, confirmed by self-report and testing. Of the enrolled participants, 43,780 were included in the final analysis after ensuring valid HIV baseline testing. The primary objective was to assess whether the adenovirus type 5 vector-based COVID-19 vaccine (Ad5-nCoV) increases the risk of HIV infection compared to a placebo. The study design allowed for the evaluation of HIV incidence over a six-month period post-vaccination.

The intervention involved administration of the Ad5-nCoV vaccine, with some participants receiving additional doses or placebo combinations depending on the specific group allocation (Groups A, B, C, and D). The comparator was a placebo. The primary outcome measured was the risk of HIV infection after vaccination. Secondary outcomes included the association between pre-existing Ad5 neutralizing antibodies and HIV incidence. Safety and tolerability data, including adverse event rates and discontinuations, were not reported in the available evidence.

Regarding the primary outcome, HIV prevalence before vaccination showed no discernible difference between the groups. Specifically, 0.39% of 21,877 participants in the placebo group tested positive, compared to 0.38% of 21,893 participants in the Ad5-nCoV group. Over the six-month follow-up, HIV incidence remained notable similar across all groups. Group A (Ad5-nCoV) reported an incidence of 0.29%, while Group B (Placebo) reported 0.21%. Group A+D (Ad5-nCoV and 1xPlacebo+1xAd5-nCoV) reported 0.27%, Group C (2xAd5-nCoV) reported 0.1%, and Group A+C+D (≥1 dose Ad5-nCoV) reported 0.25%. No increase in HIV incidence was observed in any group receiving the vaccine.

Key secondary outcomes focused on the relationship between pre-existing immunity and infection risk. The study analyzed the association between pre-existing Ad5 neutralizing antibodies (Nab) and HIV infection risk. The presence of pre-existing Ad5 Nab titers greater than 200 ratio ranged from 65.42% to 67.71% across the participating countries, with a sample size of approximately 100 participants per country. The results indicated that a heightened presence of these antibodies did not result in an increased risk of HIV infection. No statistical association was found between the antibody levels and subsequent HIV incidence.

Safety and tolerability findings were not reported in the provided data, meaning specific adverse event rates or serious adverse events could not be detailed. Discontinuations due to adverse events were also not reported. The study notes that results are specific to the Ad5-nCoV vaccine and the short-term risk window of six months. HIV status was assessed via self-report and baseline testing, with incidence measured post-vaccination. These methodological constraints limit the generalizability of the safety profile beyond this specific context.

When compared to prior concerns regarding adenovirus vector vaccines and HIV, this large-scale trial provides reassurance for the short-term safety of Ad5-nCoV in a diverse general population. However, the study does not address long-term risks beyond six months. Methodological limitations include the reliance on self-reported HIV status at baseline and the specific focus on the Ad5-nCoV vector rather than other adenovirus types. Potential biases related to the observational nature of the HIV incidence measurement post-vaccination were acknowledged, though the randomized design mitigates some confounding factors.

Clinical implications suggest that Ad5-nCoV did not increase the short-term risk of HIV infection in the studied population, regardless of pre-existing Ad5 neutralizing antibody status. Practitioners can interpret these findings as evidence that the vaccine does not pose an immediate threat to HIV-negative individuals in this context. However, questions remain regarding long-term HIV incidence beyond six months and the applicability of these results to populations with different baseline characteristics or in settings with varying HIV prevalence. Further data is needed to confirm the durability of this safety signal over longer follow-up periods.

Key takeaway: Consider that Ad5-nCoV shows no short-term HIV risk increase in 44k participants.