We're still in the early stages of the vaccine race

New clinical trial data from two experimental coronavirus vaccines — one from Oxford University and AstraZeneca in the United Kingdom, and the other from CanSino Biologics in China — are providing cautious optimism in the race to combat the pandemic.

The big picture: Science has never moved this fast to develop a vaccine. And researchers are still several months away from a clearer idea of whether the leading candidates help people generate robust immune responses to this virus.

Driving the news: The Oxford and CanSino vaccines didn't lead to any severe adverse reactions or hospitalizations, according to the results released yesterday.

• Safety — not efficacy — was the main thing these studies were supposed to be testing. And they performed well enough to move on to further trials.
• Competing candidates from Moderna and Pfizer/BioNTech have also performed well in safety trials.

Yes, but: Future trials will be the ones that tell us whether any of these potential vaccines actually trigger patients' immune systems to respond to the virus.

• In the results released yesterday, Oxford researchers gave their vaccine to 543 people but only tested 35 for "neutralizing antibodies." A separate, nonrandomized group of 10 people got a booster dose of the Oxford vaccine a month after the initial dose.
• Preliminary antibody responses from CanSino's vaccine were "disappointing" to several experts.

"It's a lot of hype," said Paul Offit, a physician and vaccine expert at Children's Hospital of Philadelphia. "It's just trying to read the tea leaves of what will be a large phase three trial."

The bottom line: There are 23 coronavirus vaccines in clinical testing right now, according to the World Health Organization.

• We now have data on the first four, but the studies mostly are confirming that the vaccines aren't severely harmful and that large-scale studies are warranted — not that they definitely work yet.
• "It is good and hopeful news indeed, but we'll only know when the large trials are done," tweeted Robert Califf, a former FDA commissioner under Barack Obama.

Go deeper: Read more about the state of the global race for a vaccine