Study suggest dual COVID-19/flu shot is more effective than individual vaccines
Moderna’s new combination vaccine triggers strong immune responses against SARS-CoV-2 and influenza, study in over 8,000 people suggests.
- 12 May 2025
- 3 min read
- by Linda Geddes
A combined mRNA vaccine against COVID-19 and seasonal influenza appears to trigger stronger immune responses against both viruses compared to existing vaccines, late-stage clinical trial data suggests.
Although COVID-19 might have faded from news headlines, there are still an estimated 2.3 billion cases a year, and roughly 1 billion influenza cases annually as well. Despite vaccines being available to protect us against both diseases, not enough people are taking them. The 2024/5 flu season in the northern hemisphere has been particularly brutal, and low vaccine uptake is thought to have contributed to its severity.
Combined shot
Several companies have been developing combination vaccines for COVID-19 and influenza in the hope that a two-in-one shot would make it easier to ensure that a higher proportion of vulnerable people get immunised against both diseases.
One such company is Moderna. Its mRNA-1083 vaccine delivers instructions to human cells, telling them to make surface proteins from four seasonal influenza strains, plus a section of the SARS-CoV-2 spike protein that triggers the strongest immunity.
A previous Phase 1/2 study in 1,206 adults found that the vaccine was well-tolerated, had a good safety profile, and triggered immune responses that were similar to, and in some cases higher than, those from the influenza and COVID-19 vaccines currently in use.
Pivotal study
The latest Phase 3 study was designed to assess vaccine-related antibody responses, safety and side effects in 4,037 US adults aged 65 years and older, and 4,024 US adults aged 50 to 64.
Half of them were given the mRNA-1083 vaccine plus a placebo vaccine (a shot of saline solution), while the other half received standard COVID-19 and seasonal influenza vaccines – including high-dose influenza vaccines for the older age group – delivered at the same time.
The research, published in JAMA, found that the combined vaccine induced comparable or higher immune responses, as measured by the number of antibodies in the blood, than when the standard vaccines were delivered together. For example, compared to the standard COVID-19 vaccine, mRNA-1083 induced a 64% higher antibody response, while compared to standard quadrivalent influenza vaccines (those protecting against four strains of flu), antibody responses induced by the combination vaccine were comparable or superior depending on the specific strain measured.
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While it is not yet known how this translates into protection against infection or disease severity, antibody levels do provide an indication of how well a vaccine might work, and how long the protection it provides might last.
Adverse reactions were slightly more common among people who received the combination vaccine – reported by 84–85% of those receiving mRNA-1083 vs. 78–82% of those receiving the standard vaccines – but these were mild to moderate, and no safety concerns were identified. The most frequently reported reactions were injection site pain, fatigue, muscle ache and headache, and these usually disappeared within three to four days.
Researchers leading the trial said that an mRNA-based combination vaccine for COVID-19 and influenza had numerous advantages over traditional egg-based influenza vaccines, including the breadth of immunity and T-cell responses for the influenza component, and the rapid production and flexibility for updates to vaccine composition to ensure close matching to circulating influenza and SARS-CoV-2 virus strains.
“Further, the platform can quickly adapt to allow for timely and effective public health responses, especially in the face of emerging variants and strains,” they said. Earlier this month, Moderna said that it anticipated the vaccine could receive regulatory approval in the US in 2026.
