Will Flu Be Mild This Winter? FDA Approves First mRNA Flu Vaccine

Could people in the United States be headed for a relatively mild 2026-2027 flu season? I know that it’s a little early for most people to even think about influenza in August, but Australia is offering some encouraging clues. The FDA has just approved the first mRNA flu vaccine (mFLUSIVA) from Moderna. How good is it and what are the risks?

The last thing Americans want to think about in August is influenza. We are still digging in the garden, heading for the beach and going for walks in the woods. But here at The People’s Pharmacy we have long watched what happens during flu season in Australia. Because winter arrives there while Americans are enjoying summer, the Southern Hemisphere sometimes provides an early warning about what may be headed our way.

Last year, Australia was hit hard by influenza. We alerted our readers early that things could get bad during the 2025-2026 flu season in North America. We were proven right when the United States subsequently experienced a difficult influenza season as well. This year, however, the early news from Australia is surprisingly reassuring.

Is a Mild Flu Season Headed Our Way?

According to the Australian Centre for Disease Control (ACDC), the country had recorded 59,779 laboratory-confirmed influenza cases through July 26, 2026. During the same period in 2025, Australia reported 232,805 cases. That represents a decline of more than 74 percent.

Australian health authorities also reported that influenza-like illnesses and doctors’ office visits were lower than during the same period in recent years. Most of the influenza viruses analyzed, more than 78 percent, were considered a good match for the strains included in the Southern Hemisphere vaccine. That sounds like very good news.

Before we celebrate, though, Australia’s winter is not over. Health officials caution that the country may be returning to a more traditional pre-pandemic pattern in which influenza begins rising in June and peaks later in the winter, around August. In other words, the Australian season may be mild…or it may merely be late.

There is another reason not to treat Australia as a crystal ball. The viruses circulating there do not always behave exactly the same way when they reach North America. New variants can emerge, and immunity, vaccination rates, weather and human behavior differ from one country to another. Still, if influenza remains relatively subdued in Australia and the vaccine continues to match circulating strains, that would be an encouraging sign for Americans heading into the fall of 2026.

The FDA Approves the First mRNA Flu Vaccine

Just as the Australian flu report was attracting our attention, the FDA approved a radically different type of influenza vaccine. Moderna’s new product is called mFLUSIVA. It is the first licensed seasonal mRNA flu vaccine in the United States.

The agency granted conventional approval for adults between 50 and 64 years old. For people 65 and older, the FDA used its accelerated approval pathway. That distinction matters. Adults between 50 and 64 were included in a large clinical trial comparing mFLUSIVA with a conventional standard-dose influenza vaccine. People 65 and older, however, are generally advised to receive a high-dose or adjuvanted flu vaccine because their immune systems may not respond as vigorously to an ordinary shot.

The crucial clinical trial did not compare mFLUSIVA directly with one of those preferred enhanced vaccines. That became the center of a very public controversy.

Why Dr. Vinay Prasad Objected to the mRNA Flu Vaccine Trial

Vinay Prasad, MD, MPH, is a hematologist-oncologist in the Department of Epidemiology and Biostatistics at the University of California, San Francisco. He has been a guest on The People’s Pharmacy radio show and podcasts.

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Dr. Prasad and the FDA

Dr. Prasad was director of the FDA’s Center for Biologics Evaluation and Research. He initially refused to allow the agency to review Moderna’s mRNA flu vaccine application.

Dr. Prasad argued that Moderna had not used the best available standard of care as its comparator for people 65 and older. Instead of comparing its mRNA flu vaccine product with a high-dose or adjuvanted vaccine, the company compared it with an ordinary standard-dose flu shot.

Moderna countered that the FDA had previously indicated that such a comparison would be acceptable. The company also pointed out that it conducted the trial in multiple countries, some of which do not routinely recommend enhanced vaccines for older adults. After a public uproar, the FDA reversed course and agreed to review the application.

We understand Dr. Prasad’s underlying concern. A manufacturer should not be able to make a new treatment look impressive simply by comparing it with a less effective alternative. On the other hand, refusing to review the entire application may have been too sweeping. The standard-dose comparator was appropriate for people between 50 and 64, because enhanced flu vaccines are not preferentially recommended for that age group.

The FDA ultimately split the difference. It granted standard approval for those between 50 and 64, but only accelerated approval for people 65 and older.

How Much Better Was the mRNA Flu Vaccine?

The headline number is that mFLUSIVA was 26.6 percent more effective than the standard-dose comparator at preventing laboratory-confirmed influenza. That probably sounds impressive to casual observers. But that is a relative number. Relative percentages can make benefits appear larger than they look in absolute terms. Readers of The People’s Pharmacy know that absolute risk reduction (ARR) is, in our opinion, a more reasonable way to assess benefit.

We always like to go to the original research paper for meaningful numbers. In this case it was The New England Journal of Medicine, May 6, 2026.

In the trial, 411 out of 20,179 people who received Moderna’s mRNA influenza vaccine developed the flu. That was approximately 2.0 percent. Among the 20,124 people who received the standard-dose vaccine, 557 developed influenza. That was approximately 2.8 percent.

The absolute difference was therefore about 0.8 percentage points.

Put another way, roughly 14 fewer people out of every 2,000 vaccinated developed confirmed influenza with mFLUSIVA rather than the conventional shot. That suggests 1,986 did not benefit from the mRNA influenza vaccine. We also like to mention the NNT (number needed to treat). According to my calculations, about 125 people would need to receive the mRNA vaccine instead of the standard-dose vaccine to prevent one additional case of laboratory-confirmed flu during the study period.

That is a real benefit, but it is not a breathtaking one. If you told us that the new mRNA influenza vaccine prevented the flu in 9 out of 10 people treated, we would be much more excited.

The FDA has granted “accelerated approval” for mFLUSIVA for those over 65, but the agency has required Moderna to conduct a Phase 4 confirmatory study. That means the agency wants data demonstrating that the new vaccine provides clinical protection at least comparable, if not better, to a CDC-preferred vaccine for older people. The planned trial is expected to involve approximately 800,000 older people..

What About Side Effects?

Many of our readers remain uneasy about mRNA technology because of their experiences with the COVID-19 vaccines. Some believe potential problems were minimized or dismissed too quickly by public health authorities. Those concerns should not be mocked or brushed aside.

The mFLUSIVA trial did not uncover a broad new safety problem, and serious adverse events were generally uncommon. Nevertheless, the mRNA shot produced considerably more short-term reactions than the conventional vaccine.

About two-thirds of mFLUSIVA recipients reported pain at the injection site. That was more than double the number of localized reactions to the standard flu shot.

Approximately 45 percent experienced fatigue vs. 20 percent getting the standard vaccine. About 38 percent complained of a headache after the mRNA influenza vaccine compared to 18 percent on a regular flu shot. Muscle pain or myalgia occurred in 35 percent of the people getting mFLUSIVA vs. nearly 12 percent who received a standard jab.

The investigators noted that:

“Serious adverse events were reported in 2.2% of recipients of mRNA-1010 and 1.9% of recipients of standard-dose comparator through the data-cutoff date…”

But even a trial enrolling more than 40,000 people may be too small to identify a very rare adverse reaction reliably. That does not mean the vaccine is unsafe. It means that rare risks often become clearer only after hundreds of thousands or millions of people have received a new product.

The Biggest Unanswered Question for Seniors

Adults 65 and older account for a disproportionate share of serious influenza complications and deaths. They are also the group for whom the evidence about mFLUSIVA is least satisfying. The FDA granted accelerated approval based largely on immune responses. The Moderna vaccine produced stronger antibody levels than Fluzone High-Dose against the selected influenza strains. Antibody measurements can be useful, but they are not the same as demonstrating that substantially fewer people were hospitalized or died.

Until those results are available, people over 65 will be asked to make a decision without the kind of direct clinical comparison many would reasonably prefer. Will mFLUSIVA prevent a lot more actual cases than a high-dose flu vaccine? Will it dramatically reduce hospitalizations? Will its additional side effects be worth any added protection? Will rare complications emerge when it is used on a much larger scale? At this point, we do not have convincing answers.

Where Does This Leave People Planning a Flu Shot?

We have tracked flu vaccine performance for decades. The average effectiveness over the years has been approximately 42 percent, with results ranging from a discouraging 10 percent in one season to about 60 percent in another. That is a long way from perfect protection.

Influenza vaccines may nevertheless reduce the likelihood of infection and, in some seasons, the risk of hospitalization. For an older person or someone with heart disease, lung disease, diabetes or a weakened immune system, even partial protection may be worthwhile.

People between 50 and 64 will soon have another choice. They can select an established egg-based or cell-based flu vaccine, or consider the new mRNA option. It should be available for the coming flu season. The large trial in the New England Journal of Medicine suggests that mFLUSIVA prevented somewhat more flu than a standard-dose vaccine, but it also caused substantially more temporary reactions.

People 65 and older face a more complicated choice. High-dose and adjuvanted vaccines already have years of clinical experience behind them. Although mFLUSIVA generated strong antibody responses, we do not yet know whether it offers better real-world protection than those enhanced vaccines. That is why the FDA is requiring a massive follow-up study.

The Bottom Line on the mRNA Flu Vaccine

Australia’s experience gives us reason for guarded optimism this coming flu season. Influenza cases there have been far lower than they were last year, and most tested viruses have matched the vaccine strains pretty well. But the Australian season is not finished, and influenza remains notoriously unpredictable.

The FDA’s approval of mFLUSIVA is scientifically significant. It could eventually lead to faster vaccine production and better strain matching. For adults between 50 and 64, the vaccine prevented more flu than a standard-dose shot, although the absolute improvement was less than one percentage point.

For adults 65 and older, the most important questions remain unanswered. The FDA has allowed the vaccine to be used in older adults. It has also required Moderna to demonstrate meaningful clinical benefit compared with the enhanced vaccines already available to seniors.

We would like to hear from you. Are you comfortable receiving an mRNA influenza vaccine, or would you prefer one made with older technology? Would somewhat better protection outweigh a greater likelihood of short-term reactions? Are you someone who skips the flu shot entirely? We would love to get your perspective as well.

Please share your experience and perspective in the comment section below where it says “View Comments.” If you think your friends and family members may be reading about the new mRNA flu vaccine, why not send them this article? We like to think we provide context beyond the health headlines. We appreciate your support this way because you allow The People’s Pharmacy to keep moving forward. Thank you.