Moderna Inc said on Wednesday its experimental COVID-19 vaccine induced immune responses in older adults similar to those in younger participants, offering hope that it will be effective in people considered to be at high risk for severe complications from the coronavirus.

The company is one of the leading contenders in the race to develop a vaccine against the virus that has killed more than 820,000 people worldwide. Its candidate, mRNA-1273, is already in late-stage human trials testing its ability to safely prevent infection.

The latest data from an early Phase I study includes an analysis from 20 additional people detailing how the vaccine performed in older adults.

The analysis looked at subjects given the 100-microgram dose being tested in the much larger Phase III trial. Moderna said the immune responses in those aged between ages 56 and 70, above age 70 and those 18 to 55-years-old were similar.

Health officials have been concerned about whether vaccine candidates would work in older people, whose immune systems typically do not respond as strongly to vaccines.

Moderna shares, which have more than tripled in value this year, rose about 6% after the data’s release.

The company has so far enrolled over 13,000 participants in its late-stage study. About 18% of the total participants are Black, Latino, Native American or Alaska Native, groups that have been particularly hard hit by the pandemic, and are often under represented in clinical trials.

Dr Jacqueline Miller, Moderna’s head of infectious disease development, told a US Centers for Disease Control and Prevention (CDC) panel the company plans to post weekly updates on enrollment of Black and Latino trial subjects on its website.

Pfizer Inc told Reuters last week that 19% of the 11,000 subjects already enrolled in its vaccine trial are Black or Latino.

Miller said the demographic makeup of Moderna’s trial is a frequent topic at meetings with U.S. officials heading the White House program aimed at accelerating development of COVID-19 vaccines and treatments.

Deep Freeze

Companies and health officials also are working on ways to distribute COVID-19 vaccines, some of which must be shipped and stored at extremely cold temperatures.

Dr Nancy Messonnier, director of the CDC’s National Center for Immunization and Respiratory Diseases, questioned Pfizer’s plans after the company said its vaccine must be stored at ultra-low temperatures for up to 6 months or in specially designed shipping containers for up to 10 days.

Once removed from the containers, the vaccine can be kept for up to a day at a temperatures between 2 and 8 degrees Celsius (36-46°F) – roughly the temperature of a normal refrigerator – or 2 hours at room temperature.

“The complexities of this plan for vaccine storage and handling will have major impact in our ability to efficiently deliver the vaccine,” Messonnier said.

Pfizer told the CDC panel it is working on making the vaccine stable at higher temperatures. Pfizer shares were down about 1.5%.

Moderna’s vaccine has to be kept at minus 20 degrees Celsius for shipping and longer-term storage of up to six months, but it can be kept at regular refrigeration temperatures for up to 10 days. The vaccine will be distributed in 10-dose vials with no preservatives, the company said.

Moderna is also working to make the vaccine stable at higher temperatures, Miller said.

Moderna, which has never brought a vaccine to market, has received nearly $1 billion from the U.S. government under its Operation Warp Speed program. It has also struck a $1.5 billion supply agreement with the United States.