July 20 (UPI) -- A vaccine against COVID-19 developed in China appears to be safe and effective at fostering an immune response against the virus in a small trial, a study published Monday by The Lancet shows.
Ninety-five percent of study participants who received a high dose of the experimental vaccine and 91% of those given a lower dose had immune responses to the new coronavirus, SARS-CoV-2, within 28 days of receiving a shot, according to the researchers.
The vaccine is based on a weakened human common cold virus, or adenovirus, that can infect human cells but is incapable of causing disease, the researchers said.
The adenovirus is designed to deliver genetic material for the coronavirus' spike protein to human immune cells, which can then create antibodies capable of recognizing the spike protein and fighting off the coronavirus, they said.
Phase 3 trials -- which assess safety and effectiveness in larger numbers of participants and must be completed before a vaccine or drug can be approved for widespread use -- are already underway, they said.
"This is an important step in evaluating this early-stage experimental vaccine," Feng-Cai Zhu, of the Jiangsu Provincial Center for Disease Control and Prevention in China, said in a press release.
An ideal vaccine against the new coronavirus would be effective after one or two vaccinations, work in target populations -- including older adults and those with underlying health conditions -- and offer protection for a minimum of six months, he said.
The Phase 2 trial of the experimental vaccine was conducted in Wuhan in April, Zhu and his colleagues said.
In all, 253 people received a high dose of the vaccine, developed by Chinese drugmaker CanSino Biologics, while 129 received a low dose, they said.
About 70% of participants in both groups reported mild side effects, including fever, fatigue and injection-site pain, according to the researchers.
However, compared with younger participants, older participants generally had significantly lower immune responses after receiving the vaccine, the researchers said.
"Since elderly individuals face a high risk of serious illness and even death associated with COVID-19 infection, they are an important target population for a vaccine," Wei Chen, one of the researchers involved in the study, said in a press release.
"It is possible that an additional dose may be needed in order to induce a stronger immune response in the elderly population, but further research is underway to evaluate this," said Chen, of the Beijing Institute of Biotechnology in China.