Updated: May 18, 2020 2:59 PM EDT | Originally published: May 18, 2020 12:27 PM EDT

Earlier today, the biotech company Moderna reported positive results from a phase 1 study of its experimental COVID-19 vaccine, which was among the first to begin testing in healthy human volunteers in mid-March.

The study, led by the National Institute of Allergy and Infectious Diseases (NIAID) at the National Institutes of Health, involves 45 healthy people who received one of three different doses of the vaccine. According to Moderna, there are encouraging early signs that the shot generates antibodies against the COVID-19 virus, SARS-CoV-2, in levels that were similar to or higher than those seen in the plasma of people who recovered from infections.

The phase 1 study is actually not designed to measure effectiveness of the vaccine—it is focused primarily on safety. Nevertheless, the hints of efficacy emerging from the trial are encouraging. The level of antibodies seen in the participants show that the vaccine can attract and awaken the body’s immune response to mount a defense against SARS-CoV-2. The data also hinted that the higher doses prompted stronger immune responses.

In addition, the company reports that in a preliminary analysis, antibodies from eight of the participants (four given the low dose and four given the medium dose) appeared to neutralize the virus in the lab.

“Honestly we saw this data…and were pretty elated,” says Dr. Stephen Hoge, president of Moderna. It hit on almost every point we could hope for. What these results show is that the vaccine works to the best of anybody’s ability to test a vaccine prior to a [final] phase 3 study. And by works, we mean that it generated high quality, neutralizing antibody responses. The truth is, we’ve got a really product and potentially protective immune response here.”

In the phase 1 study, the participants were all healthy volunteers aged 18 to 55 years. Those in the low- and medium-dose groups received two doses about a month apart, in order to properly prime the immune system for the most robust response. People in the highest dose group received only one inoculation. The results will likely be analyzed and reported in a scientific publication in coming weeks.

Based on these results, the phase 2 study, which the Food and Drug Administration (FDA) has cleared, will enroll around 600 healthy volunteers, will include just two doses—one that is slightly higher than the lowest dose, as well as the medium dose, since these appear to be sufficient to generate a relatively strong immune response. The company expects those trials to begin in June, and may include those at higher risk of exposure to SARS-CoV-2, such as health care workers. Those studies will determine which dose will be tested in the final, phase 3 studies that could begin as early as July. Based on the urgent need for a vaccine against COVID-19, on May 12 the FDA gave Moderna’s vaccine fast track status, which would expedite the regulatory agency’s review process.

These findings, though still early, are a validation of Moderna’s technology, which veers from the traditional vaccine design that generally depend on snippets of viral proteins or inactivated virus to activate the immune system. Moderna’s vaccine is made of mRNA from the virus, the genetic material that codes for proteins; after inoculation, it can prompt the body’s immune cells to recognize it as foreign and launch attacks against it. The company has been developing mRNA vaccines against a number of other disease, including respiratory syncytial virus, Zika and influenza.

Contact us at letters@time.com.

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