Moderna mRNA Flu Vaccine Trial Reports Mixed Results, Higher Adverse Reaction Rate

Moderna's headquarters in Cambridge, Mass., on May 8, 2020. (Maddie Meyer/Getty Images)

A large-scale human trial of Moderna’s mRNA seasonal flu vaccine yielded mixed interim results in terms of effectiveness and safety, the company said Thursday.

The experimental vaccine, called mRNA-1010, is developed using the same technology as Moderna’s COVID-19 vaccines. It works by instructing the body’s cells to assemble hemagglutinin, a protein on the surface of the virus, to trigger an immune response and prepare the body to protect itself from future exposure.

For the phase 3 trial, Moderna tested mRNA-1010 against a licensed vaccine on four strains circulating in the Southern Hemisphere: A/H1N1, A/H3N2, B/Yamagata, and B/Victoria. In interim results published Thursday, the company found that mRNA-1010 was superior in creating antibodies against both of the A strains.

When it comes to antibody levels, Moderna said mRNA-1010 was superior against A/H3N2 and equal to the existing product for A/H1N1.

However, the experimental vaccine fell short of the approved vaccine against the B strains. According to the U.S. Centers for Disease Control and Prevention (CDC), both types A and B can be equally severe, although the B viruses can only pass from human to human and is normally less common.

Morderna also reported a higher rate of solicited adverse reactions (SRAs) in participants taking mRNA-1010 (70 percent) than those who received the already approved vaccine (48 percent). The most commonly reported SRAs were pain and swelling right after the injection, headache, myalgia, and fatigue, with younger adults being more likely to be affected than older people.

The company described the experimental shot was “generally well-tolerated.”

“No significant differences in unsolicited adverse events, serious adverse events, or adverse events of special interest were observed between the mRNA-1010 and comparator groups,” it said.

The trial enrolled 6,102 adults across Argentina, Australia, Colombia, Panama, and the Philippines during the Southern Hemisphere influenza season. Participants were randomly assigned to receive either a single dose of the Moderna shot or a single dose of an approved vaccine as a comparator.

A phase 3 efficacy study is also being conducted in Northern Hemisphere countries and has reached 200 confirmed cases. Moderna said almost all of those cases were caused by the type A viruses, which is consistent with the dominant strains for this influenza season.

“While we did not achieve non-inferiority for the influenza B strains which are more frequent in younger populations, we have already updated the vaccine that we believe could improve immune responses against influenza B and will seek to quickly confirm those improvements in an upcoming clinical study thanks to the agility of our mRNA platform,” Moderna president Stephen Hoge said in a press release.