The next few months will be an important time for researchers who are developing vaccines to protect against the novel coronavirus. But health experts warn that people should not get their hopes up too high for such a vaccine any time soon.

About 15 COVID-19 vaccine studies are taking place worldwide. Vaccines train the body to recognize and fight off invading germs. Yet scientists do not know just how strong of an immune response is needed to protect people. Nor do they know the best way to develop a vaccine against the virus.

Currently, only China is developing "inactivated" vaccines: ones made by growing the new coronavirus and killing it. Inactivated vaccines, considered to be somewhat old-fashioned, are dependable but require high-security laboratories to produce. Polio shots and some influenza vaccines are made in this way.

Most other possible vaccines target not the whole germ but a major piece of it -- the "spike" protein. This protein is on the surface of the coronavirus and helps it invade human cells.

Researchers at Britain's University of Oxford have another idea. They have genetically engineered a chimpanzee cold virus so that it will not spread. But the genetically engineered virus can carry the gene for the spike protein into just enough cells to trick the human immune system into thinking that an infection is coming.

In the United States, biotechnology company Moderna and the National Institutes of Health are working on a vaccine that carries a piece of the coronavirus genetic code. This information tells the body to produce harmless spike copies that the immune system learns to recognize.

Doctor Anthony Fauci heads the U.S. National Institutes of Health, or NIH. He told The Associated Press that researchers must test thousands of people not where infection rates are rising, but where the virus is found at low levels.

The reason is that scientists need to be able to study the health of vaccine volunteers several weeks after the virus starts spreading through their community.

Because there are too few new infections locally to get clear answers, some researchers are testing vaccines in other countries. For example, British and Chinese researchers are testing possible vaccines in Brazil and the United Arab Emirates.

The United States is set to open the largest vaccine trials in July -- about 30,000 individuals. Those men and women likely will be divided among U.S. citizens and volunteers in other countries, such as Brazil or South Africa, Fauci said.

While he is hopeful, the NIH chief remains cautious. "We've been burned before," he said.

About a month after the U.S. trial begins, British researchers will launch tests that are expected to involve another 30,000 people.

Animal research suggests COVID-19 vaccines could prevent serious disease but may not completely block infection. One study showed vaccinated animals avoided being infected with pneumonia but had some virus left in their noses and throats. Whether it was enough to spread to the unvaccinated is not known.

Yet anything to avoid or even reduce symptoms 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 Drew Weissman, a doctor at the University of Pennsylvania.

The first vaccines might be replaced with later, better replacements, as historically happens in medicine, noted David Ridley, a health economist with Duke University in North Carolina.

And while injections in the arm are the fastest to make, those for respiratory diseases require virus-fighting antibodies to make their way into the lungs. Oxford lead researcher Sarah Gilbert said her team will eventually explore delivery of a vaccine through the nose.

Many vaccine successes around the world are needed.

"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 is time to set public expectations. Many scientists do not expect a coronavirus vaccine to be nearly as protective as the measles shot.

But if the best COVID-19 vaccine is only 50% effective, "that's still to me a great vaccine," said the University of Pennsylvania's Weissman.

"We need to start having this conversation now," he added, so people will not be surprised.

I'm John Russell.

Lauran Neergaard reported on this story for the Associated Press. John Russell adapted her report for VOA Learning English. George Grow was the editor.

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immune – n. of or relating to the body's immune system

response – n. reaction

old-fashioned – adj. out of date; older; opposite of modern

trial – n. a kind of testing and research that aims to show that vaccines work and are safe

cautious – adj. careful; watchful

pneumonia – n. medical a serious disease that affects the lungs and makes it difficult to breathe

symptom – n. a change in the body or mind which shows that a disease is present

respiratory – adj. medical of or relating to breathing or the organs of the body that are used in breathing

antibody – n. medical: a substance produced by the body to fight disease

delivery – n. the action of supplying or moving something

conversation – n. a talk involving two people or more people

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