As the race to develop an effective vaccine against COVID-19 surges forward, China’s entry dropped behind after results showed that older patients in its Phase II trials didn’t respond as well as expected. China’s CanSino Biologics reported preliminary results Monday that revealed that older trial participants had significantly weaker immune responses to the vaccine.

The Oxford University-AstraZeneca coronavirus vaccine candidate, another top contender in the race, also published Phase II results Monday in the journal The Lancet that showed it’s safe and induces a strong immune response, according to The Week.

According to Yahoo, the disappointing results from the CanSino Biologics vaccine may be because the vaccine is made from the adenovirus that causes the common cold in humans. On the other hand, the Oxford University-AstraZeneca vaccine uses an adenovirus found in chimpanzees.

Experts say that the weakened response to the CanSino vaccine candidate was probably caused by the immune systems of the study's participants attacking the familiar component of the vaccine, the cold virus, instead of the new coronavirus.

Both CanSino and Oxford-AstraZeneca are planning large scale Phase III drug trials and experts say that overall, Monday’s results show that that “each of these vaccines is worth taking all the way through to a Phase III study,” Dr. Peter Jay Hotez, an expert on vaccine development at Baylor College of Medicine, told The New York Times. “That is all. All it means is ‘worth pursuing.’”