FILE - This March 16, 2020 file photo shows vials used by pharmacists to prepare syringes used on the first day of a first-stage safety study clinical trial of the potential vaccine for COVID-19, the disease caused by the new coronavirus, at the Kaiser Permanente Washington Health Research Institute in Seattle. Announced Thursday, April 16, 2020, a U.S. study of a potential COVID-19 vaccine is being expanded to include older adults, the age group most at risk from the new virus. (AP Photo/Ted S. Warren)

FILE - This March 16, 2020 file photo shows vials used by pharmacists to prepare syringes used on the first day of a first-stage safety study clinical trial of the potential vaccine for COVID-19, the disease caused by the new coronavirus, at the Kaiser Permanente Washington Health Research Institute in Seattle. Announced Thursday, April 16, 2020, a U.S. study of a potential COVID-19 vaccine is being expanded to include older adults, the age group most at risk from the new virus. (AP Photo/Ted S. Warren)

A U.S. study of a potential COVID-19 vaccine is being expanded to include older adults, the age group most at risk from the new coronavirus.

The shot, made by the National Institutes of Health and Moderna Inc., is being tested in healthy young and middle-aged adults in Seattle and Atlanta.

Moderna announced Thursday the study is expanding to include older adults, divided into two age groups -- 51 to 70 and those over 70.

NIH said it is seeking 60 older adults, bringing the total being tested in the initial phase to 105.

Moderna also announced new funding from the U.S. government to speed development of the shot code-named mRNA-1273, including preparations to ramp up production and to get ready for larger, next-step studies.

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Earlier this week, NIH infectious disease chief Dr. Anthony Fauci told The Associated Press the safety study was showing “no red flags” and he hoped the next phase of testing could begin around June.

The NIH shot is one of three leading candidates in the international search for a vaccine.

A candidate made by CanSino Biologics has begun the second phase of testing in China. Another, made by Inovio Pharmaceuticals, opened its first U.S. study last week and just received funding to begin similar test vaccinations in South Korea.

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