An illustration of the new coronavirus that causes the disease COVID-19. Image courtesy of the Centers for Disease Control.

People on six continents already are getting jabs in the arm as the race for a COVID-19 vaccine enters a defining summer, with even bigger studies poised to prove if any shot really works – and maybe offer a reality check.

Already British and Chinese researchers are chasing the coronavirus beyond their borders, testing potential vaccines in Brazil and the United Arab Emirates because there are too few new infections at home to get clear answers.

The U.S. is set to open the largest trials – 30,000 people to test a government-created shot starting in July, followed about a month later with another 30,000 expected to test a British one.

Those likely will be divided among Americans and volunteers in other countries such as Brazil or South Africa, Dr. Anthony Fauci of the National Institutes of Health told The Associated Press.

While he’s optimistic, “we’ve been burned before,” Fauci cautioned.

Multiple successes, in multiple parts of the world, are vital.

“This isn’t a race of who gets there first. This is, get as many approved, safe and effective vaccines as you possibly can,” Fauci said.

Vaccine experts say it’s time to set public expectations. Many scientists don’t expect a coronavirus vaccine to be nearly as protective as the measles shot.

If the best COVID-19 vaccine is only 50 percent effective, “that’s still to me a great vaccine,” said Dr. Drew Weissman of the University of Pennsylvania.

“We need to start having this conversation now,” so people won’t be surprised, he added.

And for all the government promises of stockpiling doses in hopes of starting vaccinations by year’s end, here’s the catch: Even if a shot pans out – and it’s one that your country stockpiled – only some high-risk people, such as essential workers, go to the front of a very long line.

“Will you and I get vaccinated this year? No way,” said Duke University health economist David Ridley.

Animal research suggests COVID-19 vaccines could prevent serious disease but may not completely block infection. One study that dripped the coronavirus into monkeys showed vaccinated animals avoided pneumonia but had some virus lurking in their noses and throats. Whether it was enough to spread to the unvaccinated isn’t known.

Still, that would be a big win.

“My expectations have always been that we’ll get rid of symptomatic disease. From what we’ve seen of the vaccines so far, that’s what they do,” said Weissman.

The initial vaccines might be replaced with later, better arrivals, as historically happens in medicine, Ridley said.

And while shots in the arm are the fastest to make, those for respiratory diseases require virus-fighting antibodies to make their way into the lungs. Oxford University lead researcher Sarah Gilbert said Oxford eventually will explore nasal delivery.