Volunteers had yet to test a variety of COVID-19 vaccines

Two COVID-19 vaccines may be close to the finish line, but scientists warn it’s critical that enough people volunteer to help finish the study of other candidates in the United States and around the world.

Moderna Inc. and competitor Pfizer Inc. recently announced preliminary results showing their vaccines appear to be more than 90 percent effective, at least for short-term protection against COVID-19.

If those early results hold up and U.S. regulators agree the shots are safe, the emergency use of small rationed stocks could begin in late December. Other countries with early-dose contracts would undertake their own reviews.

But more vaccines will be needed to meet global demand and help end the pandemic, raising concerns that studies that have yet to enroll thousands of volunteers could be ending soon if people wait for an already OK option instead.

“We don’t want that to happen,” said Dr. James Cutrell, an infectious disease expert at UT Southwestern Medical Center in Dallas.

Aside from supplies, other COVID-19 vaccines in development may work differently in different populations and “we will likely benefit from having a menu of vaccine options,” Cutrell said.

“We still need volunteers,” said National Institutes of Health director Francis Collins, urging Americans to enroll.

Additionally, the participants in the Moderna and Pfizer studies who originally had sham injections would almost certainly have offered the real vaccine if the U.S. Food and Drug Administration allowed it for emergency use. But no one knows how long the protection will last, which means that even those studies must continue to monitor recipients in some way.

“It’s one thing to be effective two months after your last vaccination and another thing to be effective a year later,” said Dr. Jesse Goodman of Georgetown University, former director of the FDA’s vaccines division. “It will be really important to complete these clinical trials and the studies of the other vaccines so that comparisons can be made.”

Promising news from Moderna and Pfizer bodes well for some of their competitors, said Dr. Anthony Fauci, the U.S. government’s leading infectious disease expert whose NIH team helped develop the Moderna candidate.

Those shots target the surface-fixing “spike” protein of the coronavirus, and early results show it’s enough to generate “a protective response,” Fauci said. “Conceptually this looks good” for other spike-focused vaccines made in different ways.

Here is a table of the scores of the top players in the global vaccine race:

GENETIC CODE VACCINES

The Moderna-NIH vaccine and the candidate developed by Pfizer and its German partner BioNTech are not made with the coronavirus itself, meaning there is no chance anyone could catch it from the shots.

Instead, the vaccines are made with brand new technology that injects a piece of genetic code for the spike protein. That messenger RNA, or mRNA, instructs the body to make a harmless spike protein, enough to trigger the immune system to react if it later encounters the real virus.

There are no licensed mRNA vaccines for people, so scientists had no idea whether or how well COVID-19 candidates might work.

Both manufacturers are working to increase production at plants in the United States and Europe. They can’t just partner with other vaccine companies to take on some of the work because the technology is so different from how most shots are made today.

“It’s not a very quick or easy exchange,” said Stephane Bancel, CEO of Moderna.

VACCINES FOR TROJAN HORSES

A different way to target the spike protein: use another harmless virus to carry the spike gene around the body. Again, the body produces some peak proteins and triggers the immune system.

The British University of Oxford and AstraZeneca are making their own version of this “viral vector” vaccine with a cold virus, or adenovirus, that normally infects chimpanzees. Studies on tens of thousands of people are ongoing in the UK, the US and many other countries.

Johnson & Johnson is using a human adenovirus for its version and is the only option in advanced US tests that aim to show if a single dose instead of two would be enough.

The Chinese government has cleared the emergency use of CanSino Biologics’ adenovirus shots in the military before any final testing. Likewise, Russia has started offering an adenovirus vaccine ahead of late stage testing.

PROTEIN VACCINES

Novavax makes its vaccine candidate by culturing harmless copies of the coronavirus spike protein in the lab and packing them into virus-sized nanoparticles.

There are protein-based vaccines against other diseases, so it’s not as new as some of its competitors. Novavax has started a large final phase study in Britain and will soon begin another in the United States

“KILLED” VACCINES

Spike-focused vaccines aren’t the only option. Making vaccines by growing a virus that causes disease and then killing it is a tried and tested approach – that’s how Jonas Salk’s famous polio shots were made.

China has three so-called “inactivated” COVID-19 vaccine candidates in final testing in several countries and allowed emergency use in some people before the results. An Indian company is testing its inactivated candidate.

Preparing the virus safely and then killing it takes longer than new technologies. But inactivated vaccines give the body a preview of the germ itself rather than just that single peak protein.

The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Education. The AP is solely responsible for all content.