China has announced the completion of a Phase 1 clinical trial for a replication-competent HIV vaccine candidate that uses the Tiantan vaccinia strain, originally developed for the country’s smallpox vaccination program.
The trial, conducted in 2025 and involving 48 healthy adult participants, reported that the vaccine was safe and generated HIV-specific immune responses.
According to researchers, the vaccine employs a “DNA prime and replicating vaccinia boost” strategy. In this approach, participants first receive a DNA-based primer designed to introduce HIV antigens to the immune system.
This is followed by a booster shot using the replication-competent Tiantan vaccinia vector, which is intended to amplify and prolong the immune response.
The Tiantan strain has historical significance in China’s public health system, as it was widely used during the country’s smallpox eradication campaign.
Its established safety profile made it an attractive platform for modern vaccine development. By leveraging a replicating viral vector, scientists aim to stimulate stronger and more durable immunity compared to non-replicating approaches.
Phase 1 trials are primarily designed to evaluate safety and immunogenicity rather than effectiveness.
In this case, researchers reported no serious safety concerns among the 48 participants and confirmed that the vaccine triggered measurable HIV-specific immune responses. However, these early results do not demonstrate that the vaccine can prevent HIV infection.
Developing an effective HIV vaccine has been one of the most complex challenges in modern medicine. Since the 1980s, more than 300 HIV vaccine trials have been conducted worldwide.
The vast majority have not progressed beyond early-stage testing due to the virus’s high mutation rate and its ability to evade immune defenses. HIV’s genetic diversity and rapid evolution make it particularly difficult to design a vaccine that provides broad and lasting protection.
The replication-competent vector approach used in this Chinese study is seen by some researchers as a way to enhance immune durability, potentially overcoming some of the limitations observed in previous candidates. Still, experts caution that promising immune responses in early trials often fail to translate into real-world protection in larger, later-stage studies.
The next steps would typically involve Phase 2 trials to further evaluate safety and immune responses in a larger group, followed by Phase 3 trials to assess efficacy in preventing infection. Whether this candidate advances will depend on regulatory approvals and additional funding, as well as continued positive results…See More
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