by Xinhua writer Tan Jingjing
WASHINGTON, May 27 (Xinhua) -- The results of China's COVID-19 vaccine trial, the first such vaccine to reach phase 1 clinical trial, are "very impressive," a leading U.S. epidemiologist told Xinhua in a recent interview.
China's vaccine trial has been found to be safe, well-tolerated, and able to generate an immune response against SARS-COV-2 in humans, according to a study published online last Friday by medical journal The Lancet.
"The vaccine seemed to be well tolerated at the three doses tested, and vaccine recipients generated potent immune responses against the coronavirus as measured both in tests of neutralizing antibodies and T-cells," said Robert Schooley, a professor of medicine with the Division of Infectious Diseases and Global Public Health at the University of California, San Diego.
The Chinese research team conducted the open-label, non-randomised, phase 1 trial of an Ad5 vectored COVID-19 vaccine in Wuhan, China. A total of 108 healthy adults aged between 18 and 60 were recruited and allocated to three different dose groups to receive the vaccine.
The trial demonstrates promising results after 28 days and the final results will be evaluated in six months, according to a statement of The Lancet.
"Everyone had a T-cell response and most had an over 4 fold increase in neutralizing antibodies by day 28," said Schooley, adding that the immunogenicity results from the study are very impressive.
There is evidence that those who have clear pre-existing immunity to the adenovirus type 5 vector used to deliver the coronavirus antigens made less vigorous neutralizing antibody responses than those with lower levels of pre-existing immunity to adenovirus, said Schooley.
"This has been seen with other vaccines that use this approach and is one of the reasons that they don't work in all people and one of the things that limits using them repetitively in the same person -- as in providing what we commonly call 'booster' shots," he noted.
Further research is needed to observe whether there are differences in the strength of the responses in older volunteers, and whether the fall-off in T-cell immunity seen at day 28 continues, said Schooley, also editor-in-chief of Clinical Infectious Disease, a peer-reviewed medical journal published by Oxford University Press.
A randomized, double-blinded, placebo-controlled phase 2 trial of the Ad5-nCoV vaccine has been initiated in Wuhan to determine whether the results can be replicated, and if there are any adverse events up to six months after vaccination, in 500 healthy adults -- 250 volunteers given a middle dose, 125 given a low dose, and 125 given a placebo as a control, according to The Lancet.
Schooley said one of the challenges is that adenovirus type 5-based vaccines generally cannot be given repetitively as immunity to the coronavirus falls off, because the immunity to adenovirus persists and it makes subsequent responses to the vaccine less and less potent.
"Next steps here will be to see whether there are differences in immunogenicity in older people and how long the immunity persists," he said.
Immunity to natural coronavirus infection also declines rather quickly, which is one of the contributors to recurring waves of infection in the human population.
"If the vaccine immunity wanes as rapidly, and it is necessary to re-vaccinate every couple of years, they will likely need to develop a non-adenovirus type 5 based vaccine for the repeated vaccine," Schooley said.
He also stressed the importance of global cooperation in COVID-19 vaccine development, adding that collaboration across companies, countries and research groups will be essential to get different vaccine approaches into patients. Enditem
