Does the Current Flu Shot Contain mRNA?

No flu shot currently on the market uses mRNA technology. Every influenza vaccine approved and available today relies on older manufacturing methods: growing virus in eggs, growing it in animal cells, or producing a viral protein in insect cells using recombinant DNA techniques. The confusion is understandable given how much attention mRNA received during the COVID-19 pandemic, and it has become one of the more persistent misconceptions circulating on social media. Several mRNA-based flu vaccines are in late-stage clinical trials and could reach the market within a few years, but as of now, none has been licensed for public use.

What Is Actually in Your Flu Shot

The vast majority of flu vaccines given each year are manufactured using fertilized chicken eggs, a method that has been the backbone of influenza vaccine production for decades. Virus strains recommended by the World Health Organization are injected into the eggs, allowed to replicate, then harvested, purified, and either inactivated (killed) or attenuated (weakened). The result is a vaccine that trains your immune system to recognize influenza proteins without using any mRNA at all.

Two alternatives to the egg-based approach exist and are already approved. Cell-based vaccines grow the influenza virus in cultured mammalian cells instead of eggs. Recombinant vaccines skip the virus entirely: the key influenza protein, hemagglutinin, is manufactured in insect cells using a baculovirus expression system and then purified. One such product, Flublok, contains three times more hemagglutinin than traditional egg-based shots and is free of egg protein and preservatives.¹ All three platforms, eggs, cells, and recombinant, are conventional protein-based or inactivated-virus approaches. None involves mRNA.

Why People Think the Flu Shot Has mRNA

The COVID-19 pandemic made mRNA a household term almost overnight, and public understanding of which vaccines use which technology has been muddled ever since. A large-scale analysis of over 260,000 social media posts about influenza vaccination found a recurring theme: the false belief that flu vaccines now use an mRNA platform similar to the COVID-19 shots.² That belief appears to have contributed to vaccine hesitancy, with some people declining flu shots they previously accepted because they assumed the formulation had changed.

It had not. The flu vaccines offered during and after the pandemic were the same egg-based, cell-based, and recombinant products that had been available before COVID-19 arrived. No regulatory agency approved a switch in flu vaccine technology during that period. If you received a flu shot at a pharmacy or doctor’s office any time in recent years, you received a conventional vaccine.

mRNA Flu Vaccines in Clinical Trials

While no mRNA flu vaccine has been approved, several are deep into development, and the clinical results published so far are promising enough that approval could come in the near future. The two most advanced candidates are Moderna’s mRNA-1010 and Pfizer’s modified mRNA (modRNA) influenza vaccine, both of which have completed large phase 3 trials.

Moderna’s mRNA-1010 was tested against a licensed inactivated flu vaccine in a trial involving more than 40,000 adults. Among those who received the mRNA candidate, about 2% developed confirmed influenza-like illness, compared to about 2.8% in the group that received the standard vaccine. That translates to a relative vaccine efficacy of roughly 27% over and above the already-effective standard shot, meeting pre-set criteria for superiority.³ Across two phase 3 trials involving more than 14,000 vaccinated adults, mRNA-1010 showed an acceptable safety profile and stronger immune responses against influenza A strains, though responses against influenza B strains were lower relative to the comparator vaccine.⁴

Pfizer’s candidate showed a similar pattern. In a trial of roughly 18,500 participants, the modRNA vaccine demonstrated about 35% relative efficacy over a standard flu shot against influenza-like illness, again meeting criteria for both noninferiority and superiority. Almost all cases were caused by influenza A strains, and the vaccine performed well against those, though it did not demonstrate noninferiority for antibody responses against B strains.⁵

Both results deserve a note of context. The comparison was not against a placebo but against an already-licensed vaccine, so these numbers reflect an improvement on top of existing protection. The B-strain weakness in both candidates is a genuine gap that developers will need to address before regulators and physicians are fully comfortable with a switch.

The Egg Problem That Makes mRNA Attractive

There is a real reason the industry is interested in moving flu vaccines beyond eggs, and it is not just the novelty of mRNA. Growing influenza virus in chicken eggs can introduce mutations in the hemagglutinin protein as the virus adapts to avian cells. These egg-adaptation changes can make the vaccine virus look different enough from the strain actually circulating in humans that the immune response it generates is less effective.

This problem has been documented repeatedly. An expert consensus estimated that egg adaptation reduces vaccine effectiveness by roughly 4 to 16 percentage points, depending on the season and the strain. The impact is most pronounced for the H3N2 subtype and in people under 65. Over a five-season span studied, egg adaptation was significant enough to dent vaccine effectiveness in about two out of every five seasons.⁶ In one particularly well-documented case during the 2012–13 season, poor vaccine effectiveness was traced not to the circulating virus drifting away from the vaccine strain but to mutations the vaccine strain itself picked up during egg passage. Antibody levels against the egg-adapted version were reduced 16-fold compared to the cell-passaged version.⁷

mRNA vaccines sidestep this problem entirely. Because the manufacturing process involves synthesizing a genetic sequence in a lab rather than growing a live virus in eggs, there is no opportunity for egg-adaptation mutations to creep in. The protein your cells produce after vaccination should be a closer match to what is actually circulating. This is one of the strongest scientific arguments for the technology, independent of whether it turns out to be more effective in clinical trials.

How an mRNA Flu Vaccine Would Work

If an mRNA flu vaccine reaches the market, the basic mechanism would be the same one used in the Pfizer-BioNTech and Moderna COVID-19 vaccines. A strand of messenger RNA encoding a flu protein, typically hemagglutinin, is wrapped in a lipid nanoparticle, a tiny fat bubble that protects the fragile mRNA and helps it get inside your cells. Once inside, your cells read the mRNA instructions, build the flu protein on their surface, and your immune system learns to recognize it.⁸ The mRNA itself is broken down by the body within days and does not integrate into your DNA.

One practical advantage of this approach is speed. Updating an mRNA vaccine for a new flu season could be done much faster than growing new virus stocks in millions of eggs. If a late-breaking strain change is needed, the mRNA sequence can be swapped out and manufactured in weeks rather than months. That speed mattered enormously during COVID-19 and could matter just as much during an influenza pandemic, when the circulating strain might not match what was predicted months earlier.

Combination Shots on the Horizon

One of the more intriguing developments in the mRNA flu vaccine pipeline is the prospect of a single shot that protects against both influenza and COVID-19. Moderna has been developing mRNA-1083, a multicomponent vaccine encoding both seasonal influenza and SARS-CoV-2 antigens. In a phase 1/2 trial, this combination vaccine was generally well tolerated and induced immune responses against both influenza and COVID-19 that were similar to or higher than those achieved by giving the two separate licensed vaccines.⁹

The vaccine advanced to a phase 3 trial in adults 50 and older, where it was compared against receiving a standard flu shot and a COVID booster as two separate injections. The combination vaccine met its primary goal: immune responses to all four influenza strains and to SARS-CoV-2 were noninferior to the two-shot approach.¹⁰ If this product eventually gains approval, it could simplify fall vaccination significantly. Instead of two separate appointments or injections, one shot covers both respiratory viruses.

The Push Toward a Universal Flu Vaccine

Beyond seasonal flu shots, mRNA technology is being explored for something more ambitious: a universal influenza vaccine that would protect against many strains at once, potentially eliminating the need for annual reformulation. The idea centers on targeting parts of the influenza virus that change little from year to year, particularly the stalk region of the hemagglutinin protein, which is more conserved than the head region that current vaccines focus on.

Early-stage research in animals has shown encouraging results. An mRNA vaccine encoding full-length hemagglutinin and delivered in lipid nanoparticles induced antibodies targeting the stalk domain in mice, rabbits, and ferrets. In mice, these stalk-directed antibodies provided protection not just against the specific strain in the vaccine but also against related and even distantly related influenza strains.¹¹ Separate work has explored combining multiple conserved influenza antigens, including hemagglutinin stalk, neuraminidase, and other viral proteins, into a single mRNA vaccine to broaden protection further.¹²

This is still early science. Mouse and ferret data do not always translate to humans, and a universal flu vaccine has been a goal for decades without arriving. But mRNA’s flexibility makes it well-suited to the approach because encoding multiple antigens in one formulation is straightforward compared to growing and combining multiple viral proteins through conventional methods.

What This Means if You Are Getting a Flu Shot This Year

If you walk into a pharmacy or clinic for your annual flu vaccine today, you will receive one of the conventional products: an egg-based inactivated vaccine, a cell-based vaccine, or the recombinant protein vaccine. None of these is an mRNA vaccine. The pharmacist or nurse administering the shot can tell you exactly which product you are receiving, and the lot information is recorded on your vaccination card.

For people with egg allergies, cell-based and recombinant options already provide egg-free alternatives, so the arrival of mRNA vaccines is not strictly necessary to solve that particular problem. The advantages mRNA may eventually bring are subtler: better strain matching by avoiding egg adaptation, faster manufacturing turnaround when strain recommendations change late, and the convenience of combination vaccines covering multiple pathogens in a single injection.

When mRNA flu vaccines do arrive, they will go through the same regulatory review process that every vaccine undergoes before reaching the public. The phase 3 trial data published so far suggest they can outperform existing vaccines against influenza A strains, but the weaker B-strain responses need to be improved. Regulatory agencies will weigh these results alongside safety data and manufacturing consistency before granting approval.

Cell-Based and Recombinant Vaccines as an Intermediate Step

It is worth noting that the egg-adaptation problem is not being ignored while the world waits for mRNA. Cell-based flu vaccines, which grow influenza virus in cultured mammalian cells rather than eggs, reduce but do not fully eliminate adaptation-related mutations.¹³ Recombinant vaccines go further by producing the hemagglutinin protein directly, bypassing the need to grow the virus at all. The recombinant approach generates properly folded, biologically active protein that closely matches the target strain.¹⁴

These existing alternatives already address some of the shortcomings of egg-based manufacturing. If mRNA flu vaccines are approved, they will enter a landscape that has already been shifting away from eggs, and their success will depend on whether they offer meaningful clinical advantages over the cell-based and recombinant options that are already available, not just theoretical ones. The trial data comparing mRNA candidates against standard-dose inactivated vaccines are encouraging, but head-to-head comparisons against the higher-dose and recombinant products favored for older adults are what will ultimately determine where mRNA fits in the annual vaccination playbook.