With the race for a COVID-19 vaccine underway, Stanford University professor of pathology, immunology, and microbiology Dr. Bali Pulendran discussed the most promising candidates, the technologies they employ, the risks, and the dynamics of this international race.

There are at least 23 vaccine candidates in human testing, with several in final phase testing. This week the U.S.-based company Moderna shared promising results of its Phase 1 trial, with 45 out of 45 patients developing “robust” amounts of neutralizing antibodies (up to four times the amount found in recovered COVID-19 patients) and a T-cell response, without major safety concerns at a 100 milligrams dose. The fast-tracked vaccine begins a final, Phase 3 trial in 30,000 patients on July 27. Moderna’s president has stated that he expects results before December.

To receive the FDA’s approval, a COVID-19 vaccine must have a 50 percent efficacy rate as compared to a placebo. While that benchmark’s proven controversial, with some concerned it is too low, Pulendran said achieving 50 percent efficacy “on a six- or twelve-month basis” would be a promising first step, adding that the seasonal flu vaccine efficacy rate ranges from 10 percent to 90 percent. (The Centers for Disease Control and Prevention has said last year’s seasonal flu vaccine efficacy rate was 39 percent.) Other countries have not yet disclosed their criteria for approving a vaccine.

This is important because this race is international. The United States now joins China and the United Kingdom in having a vaccine candidate in final-phase testing. China has at least three; the UK’s candidate, developed out of Oxford University, in partnership with pharmaceutical giant AstraZeneca, is now in over 14,000 bodies. Oxford’s candidate uses an adenovirus (a common cold virus) as a viral vector, operating something like a Trojan horse to smuggle in a bit of the coronavirus and fool the body into creating antibodies to COVID-19.

There is an obvious currency in being the first nation to develop a vaccine. While countries like the United States are hedging bets by investing in candidates both within the country (like Moderna’s) and out of the country (like AstraZeneca’s) to ensure primary access there is still lots of hand-wringing about the major economic implications of one country’s inoculation before another.

But Pulendran is optimistic, and realistic, about this global effort.

“We are looking at a vaccine where we need several billion doses, beyond the capacity of any single manufacturing company,” he said. “It should be a collaborative effort, so we have enough coverage to vaccinate the planet.”

And so this coronavirus continues to show us, on a hyperlocal level and a global scale, how intrinsically intertwined we are.