Moderna's COVID-19 vaccine trial starts enrolling high-dose arm

A phase 1 trial of Moderna’s COVID-19 vaccine candidate has begun enrolling subjects at the highest dose. Moderna shared the update on the COVID-19 study alongside news that people in another trial had anti-Zika antibodies after receiving the biotech’s vaccine against that virus.

Vaccines were a key application of Moderna’s mRNA platform before the emergence of the pandemic SARS-CoV-2 coronavirus. But the biotech’s leading role in efforts to develop a prophylactic that could enable humanity to fully escape the current crisis has increased interest in its vaccine work. Moderna is sharing an update on the full scope of that work today at a virtual event.

Ahead of the event, Moderna issued a statement about the progress of its vaccines, revealing the National Institutes of Health (NIH)-led phase 1 study of its COVID-19 candidate mRNA-1273 has begun enrolling subjects to receive the highest dose. The trial has three arms that are administering doses of 25 mcg, 100 mcg and 250 mcg.

When NIH revealed it had dosed the first subject in the trial on March 16, it said it planned to enroll participants over approximately six weeks. Today, Moderna said the study “continues on track.”

The timeline means the world has a little longer to wait before getting an early look at clinical data on the vaccine. In the absence of clinical data on mRNA-1273, observers are scrutinizing the rest of Moderna’s pipeline of prophylactic vaccines for evidence that its mRNA-based approach works.

Moderna is providing an update on its Zika virus candidate mRNA-1893 at the vaccine day. Results shared ahead of the event showed the 10 µg and 30 µg regimens, the lowest doses used in the trial, induced seroconversion in 94% and 100% of participants, respectively. Seroconversion is the process through which people gain neutralizing antibodies against a pathogen such as Zika or SARS-CoV-2.

In sharing the data, Moderna said “a single vaccination of the 30 µg dose level was sufficient to convert baseline flavivirus seronegative participants.” However, the seroconversion rates were taken from subjects who received two doses 28 days apart. Moderna said “there was a clear benefit” to the two-dose regimen. 

Moderna also found the vaccine induced a neutralizing antibody response in seropositive subjects. In participants who already had antibodies against the virus, Moderna tracked a fourfold boost. Three quarters of subjects who received two 30 µg shots experienced such a boost. 

The Zika trial added to evidence of the safety of Moderna’s vaccine platform. Subjects reported no vaccine-related serious adverse events or adverse events of special interest. Moderna said safety “did not appear affected by the second vaccination nor a flavivirus-positive baseline serostatus.”

While the update is broadly positive, there remains a long way to go for the Zika vaccine, let alone the more closely watched COVID-19 candidate. The pace at which Moderna, by necessity, is moving forward in COVID-19 means that prospect may now serve as the proving ground for its platform.