Pharmaceutical company Pfizer has begun testing an experimental vaccine to fight coronavirus in the United States, the company announced Tuesday.

The United States-based company, working alongside German drug maker BioNTech, reported that the first human participants in the United States received the potential vaccine, BNT162. It was tested on humans since the end of last month in Germany.

“With our unique and robust clinical trial program underway, beginning in Europe and now in the United States, we look forward to moving quickly in collaboration with our BioNTech partners and regulatory authorities to bring a safe and effective vaccine to the patients who need it most. They need it, “explained Pfizer President and CEO Albert Bourla in a statement.

“In less than four months we have been able to move from preclinical studies to human testing, that is extraordinary,” he added.

The experimental vaccine contains genetic material called messenger RNA, or mRNA. MRNA is a genetic code that tells cells what to build, in this case, an antigen that can induce an immune response to the virus.

The clinical trial will test the experimental vaccine in adults between the ages of 18 and 55 in the first stage, before moving on to older groups, the company reports, adding that it expects to be tested in up to 360 people.

There are currently no FDA-approved therapies to avoid COVID-19, and drug manufacturers are competing to produce a vaccine, which health officials say is expected to take at least 12 to 18 months.

According to the World Health Organization, there are more than 100 vaccines in development worldwide as of April 30, with at least eight candidate vaccines already in human trials.

Hopes of bringing a vaccine to market are high, but scientists set low expectations for how quickly it can happen. Developing, testing, and reviewing any potential vaccine is a long, complex, and costly effort that could take months or even years, global health experts say.

The Modern biotech firm, in association with the National Institutes of Health, an agency within the Department of Health and Human Services, began the first human test for a possible vaccine in March.

Johnson & Johnson said its goal is to produce between 600 million and 900 million doses of its possible coronavirus vaccine by the end of the first quarter of 2021 if the human trials scheduled to start in September go as planned.

Pfizer expects to produce “millions” of vaccines by the end of this year, the company’s chief scientific officer, Dr. Mikael Dolsten, told CNBC last month. It is expected to increase to “hundreds of millions” of doses next year, the company said Tuesday.

Sites currently administering doses include NYU Grossman School of Medicine and the University of Maryland School of Medicine, Pfizer said. The University of Rochester Medical Center, the Rochester Regional Health Center and the Cincinnati Children’s Hospital Medical Center “will begin enrollment soon,” the company said.

Pfizer and BioNTech will work together to market the vaccine worldwide after regulatory approval.

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