CanSino Biologics Inc, one of many companies worldwide trying to develop a coronavirus vaccine, needs to conduct late-stage trials overseas if it is to stay in the race, experts say, but it has yet to announce another country willing to help.
Mid-stage trials showed that its vaccine did not work as well in people with immunity to a particular strain of the common cold virus and experts say it needs to broaden its pool of testing in Phase III trials to see if that outcome, described by the company as "the biggest obstacle", is replicated abroad.
With other countries pushing ahead with their own tests and deepening tensions with the United States posing a challenge to international collaboration, time is not on its side.
A Phase II trial on 508 participants from Wuhan, where the coronavirus outbreak was first identified late last year, was promising and safe, inducing an immune response in most of the volunteers who got one dose, the company said.
But the study showed signs that people who had previously been exposed to a particular adenovirus in the shot had a reduced immune response.
The vaccine uses a harmless cold virus known as adenovirus type-5 (Ad5) to carry genetic material from the coronavirus into the body.
"There is a large fraction of people both in the Western world and particularly in the developing world that have the baseline Ad5 neutralizing antibody," said Dr. Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center in Boston.
"And how will that impact the vaccine? It will reduce it... They (CanSino) will need to show that it's immunogenic in the areas of the world with the highest baseline Ad5 titers (levels) if they want to make it a global solution," he said.
CanSino's co-founder said this month that it was in talks with Russia, Brazil, Chile and Saudi Arabia to launch a Phase III trial.
Chilean Science Minister Andres Couve told Reuters that its committee has had meetings to discuss various vaccine candidates, including CanSino's, for "analysis".
CanSino did not respond to a Reuters request for comment on its overseas trial plans.
"The ideal solution would be to make the Phase III trial large and multinational, so involving as many people as they can so that any impact of different previous exposure is sufficiently diluted," said Paul Griffin, a professor at the University of Queensland.
TRUMP AND THE 'CHINA VIRUS'
Research data show that people in the United States have a lower pre-existing immunity to Ad5.
But growing political tension between Washington and Beijing has dimmed prospects for the vaccine being widely used or even tested there as the United States and other countries move ahead with their own research.
U.S. President Donald Trump has expressed a willingness to work with China, but he also blames Beijing for covering up what he calls the "China virus" and faces widespread criticism at home for his mixed messages on the disease.
Anthony Fauci, the leading U.S. expert on infectious diseases, told Reuters this month he hoped China succeeds in finding a vaccine.
"I don't worry about anybody getting there first," he said.
The high prevalence of pre-existing antibodies to Ad5 has prompted some researchers to move away to other types of adenovirus, Barouch said.
Both Johnson & Johnson and the University of Oxford, which is working with AstraZeneca , for example, use different adenoviruses, called Ad26 and Chimp adenovirus respectively, for their vaccine research.
CanSino's candidate became the first in China to move into human testing in March but is running behind other potential vaccines. Two vaccines developed by Sinovac Biotech and a unit of China National Pharmaceutical Group (Sinopharm) have already been approved for Phase III trials overseas. They do not use Ad5.
CanSino's vaccine, being developed with China's military-backed research unit, has been approved for use by the military.
If history is any guide, domestic use-only could be a path for China: An Ebola vaccine, also jointly developed by CanSino and the military research unit and based on Ad5, was approved by Beijing in 2017, but it never made it to the global market.
A China-only inoculation, however, would be a hollow victory.
"There would be no point having one country very well vaccinated if the country next door wasn't," said Danny Altmann, an Immunology professor at Imperial College in London.
"We really want global solutions and global cooperation."