Is the new mRNA flu shot more effective than the standard flu shot?
Yes. In a phase 3 trial of 40,703 adults aged 50 and older, Moderna’s mRNA flu vaccine prevented about 27 percent more flu cases than a licensed standard-dose flu shot. Confirmed flu illness occurred in 2.0 percent of people who got the mRNA shot compared with 2.8 percent of those who got the standard shot.
This is the same kind of technology used in Moderna’s COVID vaccine, now turned against influenza. Instead of growing flu virus in chicken eggs (the way most flu shots are made today), the mRNA approach gives your cells a short set of instructions to make a piece of the flu virus on their own. Your immune system then learns to recognize and fight it.
The trial tested whether this faster, more flexible technology could actually outperform the flu shots we already use, especially in older adults who are most at risk of being hospitalized or dying from the flu.
What the data show
The new mRNA flu vaccine, called mRNA-1010, was compared head to head with a standard-dose flu shot in adults from 11 countries. Out of 40,703 participants, those who received the mRNA vaccine had a 2.0 percent rate of lab-confirmed flu illness, while those who got the standard shot had a 2.8 percent rate. That works out to a relative vaccine efficacy of 26.6 percent, with a 95 percent confidence interval of 16.7 to 35.4 percent, meaning the result is statistically solid and unlikely to be due to chance.
The trade-off was more soreness and fatigue. Injection-site pain occurred in 65.8 percent of mRNA recipients compared with 29.8 percent of standard-shot recipients, and 45.1 percent reported fatigue versus 20.3 percent with the standard shot. These reactions were mostly mild to moderate and faded within a few days.
Dr. Kumar’s Take
I find this study genuinely exciting. Flu still kills tens of thousands of older Americans every year, and the standard egg-based flu vaccines have been stuck at modest effectiveness for decades. A 27 percent improvement over what we already use is a meaningful jump in a field that rarely sees big gains.
What also matters to me is the safety signal. Serious adverse events were comparable between the two groups, and there were no cases of myocarditis or pericarditis, which were the rare heart inflammation concerns raised with mRNA COVID vaccines. That said, more sore arms and more fatigue are real costs. I think most people will accept a day of feeling rundown if it means a better chance of avoiding the flu, but it is something to plan around if you have a busy schedule the day after your shot.
Study snapshot
This was a phase 3, double-blind, active-controlled trial, which is the strongest type of vaccine study short of a placebo trial. Double-blind means neither the participants nor the researchers knew who got which vaccine. Active-controlled means the comparison was against an already-approved flu vaccine, not a placebo, which is the right thing to do when an effective vaccine already exists. Participants spanned 11 countries, which makes the results more applicable to different populations and flu strains.
Safety, limits, and caveats
The biggest caveat is that this trial measured one flu season in one set of countries. Flu strains shift every year, and a vaccine’s edge in one season may not hold up in another. We also do not yet know how the mRNA vaccine performs in adults under 50, in people with weakened immune systems, or over multiple seasons of repeat dosing. The higher reactogenicity, meaning the soreness and fatigue, is worth taking seriously for people who cannot afford to feel off for a day, such as caregivers or shift workers.
Practical takeaways
- If you are 50 or older, ask your doctor or pharmacist whether an mRNA flu vaccine is available in your area once it is approved and rolled out, since this trial suggests a meaningful efficacy advantage over standard flu shots.
- Plan to get any flu shot, mRNA or otherwise, on a day when you can rest the next 24 hours if needed, because side effects like sore arm and fatigue are more common with the mRNA version.
- Do not skip your flu vaccine while waiting for the mRNA version to become widely available, because a standard flu shot still provides real protection and the flu season will not wait.
Related studies and research
- Flu vaccine effectiveness: how well does it prevent severe illness in adults?
- Long daytime naps linked to higher death risk in older adults
- PPIs double iron deficiency risk: population study findings
- Single-dose psilocybin vs placebo: first double-blind depression trial
FAQs
How is an mRNA flu vaccine different from the flu shot I usually get?
Most flu shots today are made by growing flu virus inside chicken eggs over several months, then inactivating it and putting it into the vaccine. An mRNA flu vaccine skips that process entirely. It delivers a tiny set of genetic instructions that tell your own cells to briefly produce a piece of the flu virus, which then trains your immune system. Because mRNA vaccines do not need eggs, they can be designed and manufactured much faster, which is a big deal when flu strains shift quickly from season to season.
Should I worry about heart inflammation, like the cases reported with mRNA COVID vaccines?
In this trial of more than 40,000 older adults, there were no cases of myocarditis or pericarditis reported with the mRNA flu vaccine, and serious adverse events overall were similar to the standard flu shot. The heart inflammation risk seen with COVID mRNA vaccines was concentrated in young males and was rare even in that group. Different mRNA vaccines target different proteins and use different doses, so safety findings do not automatically transfer from one to another. Larger and longer follow-up studies will continue to monitor this.
Is a 27 percent improvement actually a big deal?
In flu vaccine research, yes. Standard flu shots typically prevent somewhere between 20 and 60 percent of flu cases in a given year, depending on how well the vaccine matches the circulating strains. Bumping that protection up by another 27 percent on top of what a standard shot already provides could translate into a significant reduction in flu illness, doctor visits, and hospitalizations, especially in older adults who account for most flu deaths each year. Small percentage gains add up to large numbers of prevented illnesses when you scale across millions of people.
Bottom line
A large, rigorous phase 3 trial found that Moderna’s mRNA flu vaccine prevented about 27 percent more lab-confirmed flu cases than a standard flu shot in adults 50 and older, with more short-term soreness and fatigue but no signal of serious heart-related side effects. If these results hold up across future flu seasons, mRNA technology could become the new standard for protecting the people most likely to be hospitalized or killed by influenza.
