A combination flu and COVID-19 vaccine developed by Moderna generated a higher immune response in a late-stage trial than standalone vaccines, the company said Monday.

A two-in-one shot could improve vaccination rates and reduce the burden on the health care system.

Moderna’s phase 3 clinical trial studied two groups of about 4,000 people in each. 

In one group, consisting of participants ages 65 and older, researchers compared the combo vaccine, called mRNA-1083, to the influenza vaccine Fluzone HD and Spikevax, Moderna’s COVID shot. 

In the second group, of people 50 to 64, scientists compared mRNA-1083 to the flu vaccine Fluarix and Spikevax.

The study found that not only were immune responses from the combo vaccine not inferior to the other shots, they were statistically significantly higher against three flu strains — H1N1, H3N2, and B/Victoria — as well as COVID-19.

"Combination vaccines have the potential to reduce the burden of respiratory viruses on health systems and pharmacies, as well as offer people more convenient vaccination options that could improve compliance and provide stronger protection from seasonal illnesses," Modern CEO Stéphane Bancel said in a statement. 

Pfizer and Novavax are also developing combo flu and COVID shots, but Moderna is the first to report positive phase 3 results.

“Building on the momentum of positive Phase 3 data across our respiratory portfolio, we continue to address significant unmet medical needs and advance public health,” Bancel said.

Moderna said it will present its data at an upcoming medical conference and submit the study results for publication, when they will be peer reviewed. It will then engage with regulators. 

The vaccine will not be available for this year’s flu season.

Moderna said the combination shot also appears to be safe. The majority of side effects reported were minor, the most common being injection-site pain, fatigue, muscle aches and headache. The side effects were consistent with the other vaccines monitored in the study, the company said.

Francesca Ceddia, chief medical affairs officer for Moderna, noted in a blog post that, as of last month, flu vaccine uptake in the United States was more than double COVID-19 immunization rates (48.4% vs. 22.4%). Meanwhile, COVID-related hospitalizations are higher than with the flu — and more than double among older adults.

“The convenience that a combination vaccine could offer patients may help fill this gap while simplifying and routinizing vaccination against both diseases, which could help improve compliance with public health recommendations,” Ceddia wrote.