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.

Passengers line up for the first trains out of the city
Zhang Chang | China News Service | Getty Images

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.”

-Advertisement-