Moderna’s candidate mRNA vaccine for novel coronavirus has no safety issues and is able to elicit immune responses in all the 45 participants, the interim Phase-1 results show. Phase-2 trial is under way and Phase-3 is set to begin later this month.

The interim Phase-1 analysis of Moderna’s candidate vaccine mRNA-1273 for novel coronavirus has found the vaccine to be safe and elicit immune responses in all the 45 participants.

According to results published on July 14 in The New England Journal of Medicine, the vaccine caused mild or moderate adverse events in participants enrolled in all three dosage arms. The adverse events — fatigue, chills, headache, myalgia, and pain at the injection site — were seen in more than half the participants who received the candidate vaccine. The adverse events were more common after the second vaccination. No serious adverse events were reported.

The trial evaluated two-dose vaccination schedule using three different dosages (25 microgram, 100 microgram and 250 microgram) administered on days 1 and 29. The candidate vaccine was tested on 45 participants aged 18-55 years. There were 15 participants in each dose group. The interim analysis report findings through day 57.

Dose-dependent immune responses were seen after the first and second vaccination. The vaccine elicited “binding antibodies in all participants after the first vaccination in a time- and dose-dependent fashion,” the paper says.

The paper also reports that “commensurately high neutralising antibody responses” were seen in a dose-dependent manner. Though there was seroconversion within two weeks after the first dose, the neutralising activity was low till the second dose was administered. “This supports the need for a two-dose vaccination schedule,” it says.

The amount of binding and neutralising antibodies induced by the vaccine given as two doses is “similar to those found in convalescent serum specimens”.

“If your vaccine can induce a response comparable with natural infection, that’s a winner,” Dr Anthony Fauci, Director of the National Institute of Allergy and Infectious Diseases (NIAID) told Reuters. “That’s why we’re very pleased by the results.”

But the researchers were not able to assess the durability of immune responses in all the participants as the interim analysis was based on follow-up on day 57. It will become possible to know the durability of immune responses when the participants are followed-up for one year from the day they received the second dose.

According to the researchers, the safety profile and immunogenicity findings “support advancement” of the vaccine to further clinical trials. They find that the 100 microgram dosage elicits both high neutralisation responses and CD4 T cell responses, while being more favourable in terms of vaccine safety.

A Phase-2a trial of the vaccine using 50 microgram and 100 microgram is already under way in 600 healthy adults. It is a randomised, observer-blind, placebo-controlled trial.

A Phase-3 trial to test the efficacy of the vaccine using 100 microgram dosage in a prime and boost regimen is scheduled to begin later this month, a press release says.