Moderna flu vaccine delivers mixed results in trial

Moderna Inc on Thursday said its closely-watched experimental messenger RNA-based influenza vaccine generated a strong immune response against A strains of the flu but failed to show it was at least as effective as an approved vaccine versus less prevalent influenza B.

Moderna, whose only marketed product is its COVID-19 shot, has high hopes for its flu vaccine and aims to grab large portions of the respiratory syncytial virus (RSV) and seasonal flu markets with new mRNA vaccines.

The company said its vaccine, called mRNA-1010, generated a stronger immune response for the A/H3N2 and A/H1N1 strains than the marketed vaccine it was tested against in a trial of 6,102 adults aged 18 and over across Argentina, Australia, Colombia, Panama and the Philippines during flu season there.

It failed to meet its goal of non-inferiority compared to the conventional vaccine for the B/Victoria and B/Yamagata-lineage strains, the drugmaker said.

Moderna's shares fell more than 6% in after-hours trading following publication of the results.

The U.S. company said it has already updated mRNA-1010 in a way it believes will improve immune responses against Influenza B and will test those changes.

"We have always said our goal is to produce a flu vaccine, and then to iterate it, and to fine tune it over time to really make it exceptional," Chief Medical Officer Paul Burton said in an interview.

Dr. David Boulware, an infectious disease specialist at the University of Minnesota Medical School, said he was not overly concerned about the immune response versus Influenza B.

Boulware said the immune response against the A strains demonstrated that the vaccine probably worked and Moderna's tweaks to the vaccine are likely to improve the response against the B strains.

"I consider it pretty positive," he said.

Seventy percent of those who received Moderna's shot reported mostly mild adverse reactions compared to 48% for the conventional flu vaccine. Pain and swelling at the injection site as well as headaches and fatigue were among the most commonly reported side effects.

The company also has an ongoing late-stage efficacy study on the mRNA-1010 flu vaccine, which could have data within weeks.

If that trial reads out soon, Burton said he hopes to have the data prepared and sent to regulators in the first half of this year, which could allow them to review it as soon as late 2023 or early 2024.

The flu, an infection of the nose, throat and lungs, kills 290,000 to 650,000 people worldwide annually.