The world’s biggest COVID-19 vaccine study is under way with the first of 30,000 planned volunteers helping to test shots created by the US government – one of several candidates in the final stretch of the global vaccine race.

There’s still no guarantee that the experimental vaccine, developed by the National Institutes of Health and Moderna Inc, will really protect.

The needed proof: Volunteers won’t know if they’re getting the real shot or a dummy version.

After two doses, scientists will closely track which group experiences more infections as they go about their daily routines, especially in areas where the virus still is spreading unchecked.

“Unfortunately for the United States of America, we have plenty of infections right now” to get that answer, NIH’s Dr Anthony Fauci recently told The Associated Press.

Several other vaccines made by China and by Britain’s Oxford University earlier this month began smaller final-stage tests in Brazil and other hard-hit countries.

But the US requires its own tests of any vaccine that might be used in the country and has set a high bar: The government-funded COVID-19 Prevention Network will roll out a new study of a leading candidate – each one with 30,000 newly recruited volunteers.

The massive studies aren’t just to test if the shots work – they’re needed to check each potential vaccine’s safety.

And following the same study rules will let scientists eventually compare all the shots.

Next up in August, the final study of the Oxford shot begins, followed by plans to test a candidate from Johnson & Johnson in September and Novavax in October – if all goes according to schedule.

Pfizer Inc. plans its own 30,000-person study.

That’s a stunning number of people needed to roll up their sleeves for science.

But in recent weeks, more than 150,000 Americans filled out an online registry signalling interest.

It normally takes years to create a new vaccine from scratch, but scientists are setting speed records this time around, spurred by knowledge that vaccination is the world’s best hope against the pandemic.

The coronavirus wasn’t even known to exist before late December, and vaccine makers sprang into action on January 10 when China shared the virus’ genetic sequence.

Just 65 days later in March, the NIH-made vaccine was tested on people.

If everything goes right with the final studies, it still will take months for the first data to trickle in from the Moderna test, followed by the Oxford one.

Governments around the world are trying to stockpile millions of doses of those leading candidates so if and when regulators approve one or more vaccines, immunisations can begin immediately.

But the first available doses will be rationed, presumably reserved for people at highest risk from the virus.

-AAP