The company Johnson & Johnson has begun the final part of its trial of a single-treatment, COVID-19 vaccine. The study will be one of the world's largest, testing the injection in 60,000 volunteers in the United States, South Africa, Argentina, Brazil, Chile, Colombia, Mexico and Peru.

Several other vaccines, including vaccines from drug companies Moderna and Pfizer, are already in the final part of testing.

Also Wednesday, U.S. coronavirus task force officials appeared before a committee of the U.S. Senate for questioning about the health crisis. The nation's top infectious diseases expert Anthony Fauci and the head of the U.S. Centers for Disease Control and Prevention were among those attending.

Both officials suggested that they expect a vaccine will be widely available by spring.

"We feel cautiously optimistic that we will be able to have a safe and effective vaccine, although there is never a guarantee of that," Dr. Fauci said.

News reports suggest that President Donald Trump is pushing for a speedier process than many experts support. Earlier Wednesday, Trump posted on Twitter a link to news about the new Johnson & Johnson vaccine study. The Food and Drug Administration "must move quickly," Trump wrote in the tweet.

The FDA is the government agency responsible for approval or rejection on drug candidates, including vaccines. Its chief Stephen Hahn also appeared at the senate hearing. He told the committee that FDA scientists, not politicians, will decide whether any coronavirus vaccine meets clearly stated standards that it works and is safe.

"Science will guide our decisions. FDA will not permit any pressure from anyone to change that," Hahn said. "I will put the interest of the American people above anything else."

Speaking about the vaccine candidates, Fauci added: "There is no cutting corners."

The Centers for Disease Control and Prevention, or CDC, has asked state governments to be prepared to provide vaccinations. CDC announced Wednesday that it was providing $200 million to help begin setting up operations.

The number of coronavirus-related deaths in the United States topped 200,000 this week

I'm Caty Weaver.

The Associated Press reported this story. Caty Weaver adapted it for VOA Learning English. Mario Ritter, Jr. was the editor.

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cautiously –adv. careful about avoiding danger or risk

optimistic –adj. having or showing hope for the future: expecting good things to happen

standard –n. a level of quality, achievement, etc., that is considered acceptable or desirable

cutting corners –idiom to save money or time by not following the correct procedures or rules for doing something