CanSino Bio Photo:VCG

Chinese vaccine producer CanSino's single-dose COVID-19 vaccine Ad5-nCoV showed 90.98 percent efficacy rate in preventing severe disease in interim analysis, and is effective to prevent 65.7 percent of symptomatic diseases in clinical trials conducted in multiple countries including Pakistan, Faisal Sultan, Special Assistant to the Pakistani Prime Minister on Health, announced on Monday. It became China's third vaccine to release specific efficacy data in final-stage trials.

The interim analysis in Pakistan showed 100 percent efficacy at preventing severe disease, and 74.8 percent for symptomatic diseases, Sultan said.

No severe adverse cases related to the vaccine had occurred in trials across the world.

It did not report any serious safety concerns in the trials that finally found 101 confirmed COVID-19 cases among 30,000 volunteers in the placebo-controlled trials.

Experts said the efficacy rate is "good" considering it is one of the few single-dose vaccines available in the world so far. "Normally speaking, it is difficult for a dose to achieve high antibody levels without the second dose to enhance the immunology," a Beijing-based immunological professor who asked not to be named told the Global Times on Monday.

"A 70 percent effective single-dose vaccine may be more valuable than a two-dose regimen with 90 percent efficacy," the WHO Ad-hoc Expert Group previously said in the New England Journal of Medicine. Under the same efficacy rate and capacity conditions, the single-shot vaccine doubles the amount of people being immunized.

"The single dose can vaccinate as many people as possible in the short term compared to traditional two-dose inactivated vaccines. Moreover, it relieves the pressure on production capacity and reduces the cost of administration and transportation," Shanghai-based vaccine observer Tao Lina told the Global Times on Monday.

Whether a second shot is needed to boost immunity is still being studied, and the conclusions will be released in the future, a source close to CanSino told the Global Times on Monday. Some of the volunteers in Phase I and II clinical trials of the Ad5-nCoV had already received a second booster dose, the Global Times learned.

According to CanSino's previous announcement, the Ad5-nCoV has successfully met its pre-specified primary safety and efficacy criteria at the interim analysis.

The Phase III clinical trials of Ad5-nCoV saw more than 40,000 volunteers, aged 18 and above, who were administered with the vaccine in 78 clinical trial sites across five countries in three continents, according to a notice CanSino sent to the Global Times on Monday.

The Ad5-nCoV vaccine is a recombinant adenovirus vector vaccine jointly developed by CanSino Biologics and researchers from the Institute of Military Medicine under the Academy of Military Sciences led by Chen Wei.

Unlike inactivated vaccines, CanSino's vaccine is effective with a single dose and can bring dual protection - humoral and cellular immunity - at the same time. 

Ad5-nCoV's Phase II and III trials all involved aged participants and saw no serious adverse reactions, demonstrating that it is safe for the elderly, the Global Times learned from a source close to CanSino on Monday.

The vaccine can be stored and transported at temperatures of between 2 and 8 C, and production does not require biosafety level three laboratories, which is the case with inactivated vaccines. Experts said this makes it more accessible for developing countries with limited facilities.

CanSino's global multi-center clinical trials in countries like Russia, Mexico, Pakistan, Argentina and Chile used uniform standards and organizational plans. Each center had a principal investigator and a contract research organization as partners.

The COVID-19 vaccines developed by Russia's Sputnik V, British-Swedish pharmaceutical and the US' AstraZeneca and Johnson & Johnson use a similar approach as CanSino.

The only other single-dose vaccine, produced by Johnson & Johnson, reported 66 percent overall efficacy against moderate and severe cases 28 days after vaccination. However, it did not release trials results on mild cases.