Many countries around the world are currently experiencing a new wave of COVID-19 infections caused by the Delta variant.

As a result, disease experts are working quickly to learn whether the latest version of coronavirus is making people - mainly the unvaccinated - sicker than the earlier version.

The Delta variant was first identified in India. Now, it is the main type of SARS-CoV-2 virus worldwide.

The U.S. Centers for Disease Control and Prevention warned that the Delta variant is "likely more severe" than earlier versions of the virus. This CDC report was made public on July 30.

In this report, the U.S. health agency used research in Canada, Singapore, and Scotland. This research showed that people infected with the Delta variant were more likely to be hospitalized than patients earlier in the pandemic.

In addition, it is likely that the Delta variant spreads more easily. This is also adding to a greater number of severe cases arriving at hospitals, the experts said.

In interviews with Reuters, disease experts said the research suggests a greater risk from the Delta variant. However, the study populations were limited. And the findings have yet to be reviewed by outside experts.

Doctors treating patients infected with Delta said COVID-19 symptoms appeared more quickly. And in many areas, there was an overall increase in serious cases. But experts said more work is needed to compare outcomes among larger numbers of individuals.

Shane Crotty is a virologist at the La Jolla Institute for Immunology in San Diego, California. Crotty said the clearest sign that the Delta variant may cause more severe disease comes from the Scotland study. That study found that Delta roughly doubled the risk of hospitalization compared to an earlier version of the virus.

The majority of hospitalizations and deaths from coronavirus in the United States are happening to people who have not been vaccinated. There is also evidence, however, that the vaccines do not work as well for people with poor immune systems, including the elderly.

Healthy, vaccinated individuals who contract COVID-19 will most likely experience a weak form of the disease, said Dr. Gregory Poland. He is an infectious disease expert at the Mayo Clinic, a not-for-profit healthcare provider and research center in the U.S. Or, he added, they might be asymptomatic. "But," Poland warned, "they can pass it on to family members and others who may not be so lucky."

He said people will "have to be vaccinated and masked or we will, for the fourth time now," have to suffer through another wave of the virus.

Poland said that "out of that will come worse variants." That is because the virus mutates as it spreads, producing new variants.

Other doctors said patients infected with Delta appear to become ill more quickly. They added that, in some cases, the symptoms are more severe than earlier in the pandemic.

"We are seeing more patients requiring oxygen sooner," said Dr. Benjamin Barlow. He is chief medical officer at American Family Care, a collection of urgent healthcare facilities in the U.S.

Dr. Michelle Barron is a senior medical director of infection prevention and control at Colorado's UCHealth. She compares the Delta variant to a dangerous wildfire that is spreading quickly.

Research from China suggests that the Delta variant copies itself much faster and makes 1,000 times more virus in the body compared to the original strain. This, Barron said, is the biggest danger of this new wave.

David Montefiori is director of the Laboratory for AIDS Vaccine Research and Development at Duke University Medical Center in the U.S. He said the Delta variant is more infectious and symptoms appear faster, especially for the unvaccinated.

Montefiori said on a webcast last week, "It (is) not just easier to transmit, it makes you sicker."

I'm Anna Matteo.

This story was reported for Reuters by the following: Deena Beasley in Los Angeles; Josephine Mason in London; and Julie Steenhuysen in Chicago. Anna Matteo adapted it for VOA Learning English. Susan Shand was the editor.

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variant – n. one that exhibits variation from a type, norm, or wild type : mutation

symptom – n. a noticeable change in the body or its functions that indicates the presence of a disease or other disorder : asymptomatic – medical adj. having or showing no symptoms of disease

contagious – adj. able to be passed from one individual to another through contact

immune system – n. the system that protects your body from diseases and infections

mutate – v. to cause (a gene) to change and create an unusual characteristic in a plant or animal : to cause mutation in (a gene)

original – adj. happening or existing first or at the beginning

strain – n. a group of closely related living things that look similar but possess one or more unique characteristics

transmit – v. to give or pass (information, values, etc.) from one person to another