A new study out of China suggests that it should be possible to develop a safe vaccine against COVID-19, though the effectiveness of a single shot remains unclear.
In a paper in The Lancet Friday, Chinese researchers revealed that their candidate vaccine has so far been tested in 108 healthy adults ages 18 to 60 in Wuhan, China, where the pandemic began.
One-third of the participants received a low dose, one-third a medium dose and one-third a high dose of the candidate vaccine, referred to as Ad5-nCoV. None of the participants reported serious reactions to the vaccine, though some did suffer pain at the injection site, fever, fatigue, headache and muscle pain.
Within two weeks of getting the vaccine, the immune systems of people receiving all three doses showed some level of response, with most developing a type of antibody that can attach to the virus, though not necessarily destroy it. Some also developed so-called neutralizing antibodies, which can block the virus.
The key outstanding question is whether this vaccine or other similar ones can generate enough of these neutralizing antibodies to protect people against the virus, said Peter Jay Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine in Houston.
“It looks overall like the level of neutralizing antibody, which is a special type of antibody needed for protection, is relatively low,” Hotez said.
But no one knows what level of neutralizing antibodies will be needed to protect against infection with SARS-CoV-2, the virus that causes COVID-19.
Another option, Hotez said, will be to boost the effectiveness of this type of vaccine with a second type of vaccine.
Other researchers echoed Hotez’ words of cautious optimism.
“It is exciting to see” that the vaccine triggered an immune response, said Bruce Walker, director of the Ragon Institute of MGH, MIT and Harvard, which studies the immune system and recently shifted its focus to COVID-19. “But the investigators are appropriately cautious about interpretation since we don’t know if these levels are what is needed for protection.”
There are several different types of vaccines being tested against the coronavirus that causes COVID-19. The one in this trial is called an adenovirus vaccine, because it uses a weakened cold virus to deliver genetic material to cells in the body. These cells then make a protein found on the surface of the coronavirus, spurring the immune system to create antibodies that will recognize and hopefully destroy it.
One challenge with this Ad5-nCoV vaccine, Walker said, is that it uses adenovirus 5 to deliver its payload — a cold virus that roughly half the population has been exposed to before. In those people, the immune system will clear out the cold virus before it can deliver its payload, and therefore the vaccine won’t work as well or at all.
Older people are more likely to have been exposed to the Ad5 cold virus, simply because they’ve been alive longer, meaning the vaccine is least likely to work in the people who need it the most, Walker said via email.
Other adenovirus vaccines currently being developed to fight COVID-19 use different cold viruses, including Ad26 and a chimpanzee virus, to avoid this problem, he noted.
Roughly 100 teams worldwide are currently developing vaccines, including Moderna Therapeutics of Cambridge, Mass., and the Oxford Vaccine Group, which have also reported early results from testing in people.
In the newly published trial, researchers checked for adverse reactions both one and four weeks after vaccination. One patient in the highest-dose group reported severe fatigue and joint pain, but no complaints met the most serious category of complaint.
This early-stage trial is intended to ensure safety, as well as suggest which dose should be used for larger, later-stage trials that will check again for safety and look more closely at effectiveness.
The research was funded by the National Key R&D Program of China, National Science and Technology Major Project, and CanSino Biologics.
In a statement released with the study, one of the scientists described the results as “an important milestone,” though he cautioned that a lot more research remains to be done.
“The challenges in the development of a COVD-19 vaccine are unprecedented, and the ability to trigger these immune responses does not necessarily indicate that the vaccine will protect humans from COVID-19,” said Wei Chen from the Beijing Institute of Biotechnology, who is responsible for the study. “This result shows a promising vision for the development of COVID-19 vaccines, but we are still a long way from this vaccine being available to all.”