CanSino’s Early Phase II COVID-19 Vaccine Data Shows Promise

CanSino Biologics, along with China’s military research unit, reported early data on its Phase II trial for its COVID-19 vaccine, Ad5-nCOV. The results in 508 patients showed antibody and T-cell immune responses. There were no reported serious side effects. The data was published in the journal The Lancet.

However, there are indications that a single dose will not be enough. This is fairly consistent with what is being seen with other COVID-19 vaccines, including Moderna’s and the vaccine being developed by the University of Oxford and AstraZeneca.

“With one dose, CanSino’s human adenovirus vector-based vaccine elicited receptor-binding and neutralizing antibodies in 508 patients peaking after 28 days,” wrote Philipp Rosenbaum, senior infectious diseases analyst at GlobalData. “However, in the 52% of study participants that had a high pre-existing immunity to the viral vector, both types of antibodies were only at half the level than in the group with low-pre-existing immunity. A second dose of the vaccine might solve this issue, but on the other hand reduce the number of people who can be vaccinated.”

The CanSino vaccine uses a modified common cold virus as a vector to deliver the genetic material. This is a method also being utilized by the University of Oxford and AstraZeneca. Vaccines being developed by Moderna and the team of Pfizer and BioNTech, are using mRNA delivered in lipid nanoparticles.

Naor Bar-Zeev and William Moss, with the International Vaccine Access Center at Johns Hopkins Bloomberg School of Public Health, wrote an accompanying editorial in The Lancet discussing both the University of Oxford/AstraZeneca results, also published in the journal, and the CanSino study.

“These trial reports are hugely anticipated. The results of both studies augur well for Phase III trials, where the vaccines must be tested on much larger populations of participants to assess their efficacy and safety. Overall,” they wrote, “the results of both trials are broadly similar and promising, notwithstanding differences in the vector, in the geographical locations of the populations studies, and the neutralization assays used.”

They noted that the important of the studies looking at associations of age and sex with adverse events and immunogenicity by the Chinese group and longevity of response by the British groups, particularly “given the differential burden of severe outcomes in older adults, and the emerging science around differential sex-specific vaccine effects. These COVID-19 vaccine trials are small so inferential caution is warranted, but the explorations are laudable. Ethnic diversity in both these trials was very limited.”

They also point out that the safety results seen in the two trials are reassuring. “But when things are urgent, we must proceed cautiously. The success of COVID-19 vaccines hinges on community trust in vaccine sciences, which requires comprehensive and transparent evaluation of risk and honest communication of potential harms.”

The CanSino trial also had participants older than 55 years of age. They generally showed lower antibody responses than younger patients, which may correlate with higher pre-existing Ad5 immunity. Rosenbaum points out that this “is a serious issue since older people are particularly vulnerable to SARS-CoV-2 infections. Additionally, the percentage of trial participants who produced neutralizing antibodies was low with 48% in the low-dose and 52% in the high dose group.”

Typically, higher doses of the vaccines in all the trials to date have resulted in more adverse events. GlobalData notes that one possible solution might be for the elderly to typically receive two doses while younger people could receive only one. This would likely require additional testing of pre-existing Ad5-vector antibodies in order to decide whether a booster shot was required.

“Nevertheless,” Rosenbaum wrote, “the results are promising and warrant studies with more participants, longer observation of antibody levels and multiple vaccine doses—given the urgent need for a COVID-19 vaccine. Since CanSino is the first company to publish Phase II results, it has to be seen how the level of antibodies and T-cells will compare to results of COVID-19 vaccine candidates from other companies. However, it is still unclear which antibody levels will provide protection against SARS-CoV-2 and for how long this protection will last.”