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What to Know About mFlusiva, the New mRNA Flu Vaccine

Sep 15, 2026 | Cold and Flu, Family Medicine, Featured, Infectious Diseases, Vaccines, Your Health

For the first time, adults age 50 and older in the United States can get an mRNA flu vaccine.

The U.S. Food and Drug Administration (FDA) approved mFlusiva®, the first mRNA flu vaccine, in August 2026. Moderna makes mFlusiva. It uses the same basic vaccine technology as mRNA COVID-19 vaccines. But it targets influenza.

Unlike traditional flu vaccines, mFlusiva does not contain a live or killed influenza virus, or pieces of the virus. Instead, it uses messenger RNA (mRNA). This gives temporary instructions to your immune system, your body’s natural defense system. The instructions help it learn to recognize influenza.

This new approach might even have an edge over traditional flu vaccines.

“There is some evidence that suggests mFlusiva may offer somewhat better protection against the flu than traditional flu vaccines,” says Rebecca Choudhury, MD, Assistant Professor of Medicine (Infectious Diseases), Icahn School of Medicine at Mount Sinai.

How does mFlusiva work? How well does it protect against the flu? What do we know about safety and side effects? Dr. Choudhury explains the new mRNA flu vaccine and gives advice on getting your flu shot.

Rebecca Choudhury, MD, Assistant Professor of Medicine (Infectious Diseases), Icahn School of Medicine at Mount Sinai

How does mFlusiva work, and how is it different from traditional flu vaccines?

Traditional flu vaccines show the influenza virus or parts of it to the immune system. This teaches the immune system to recognize and fight the virus later. Depending on the vaccine, that may mean a killed virus, a weakened virus, or pieces of the virus.

mFlusiva is an mRNA vaccine. It does not contain a living or dead virus. It also does not contain viral parts. The vaccine uses messenger RNA designed to produce influenza surface proteins called hemagglutinin.

An image of the mFlusiva mRNA flu vaccine. Image credit: Moderna

It’s the same basic principle used by mRNA COVID-19 vaccines. But the target is different. COVID-19 vaccines tell cells to make the coronavirus spike protein. mFlusiva tells cells to make an influenza surface protein.

“This flu vaccine is creating a different protein, but the principle of how it works is the same,” says Dr. Choudhury.

Is mFlusiva more effective than traditional flu vaccines?

In one trial in adults age 50 and older, about 2 percent of people who received mFlusiva developed influenza confirmed by lab testing within six months of vaccination. By comparison, 2.8 percent of people who received a standard-dose flu vaccine developed influenza. The mFlusiva group had a 27 percent lower rate of flu.

For adults 65 and older, there is an important caveat. People in this age group typically receive a high-dose or adjuvanted flu vaccine rather than the standard-dose vaccine used in this trial. An adjuvanted vaccine has an added ingredient that helps the vaccine work better.

Studies comparing the immune response to mFlusiva with a high-dose flu vaccine have been encouraging. Immune response means how the body reacts to a vaccine to build protection.

“However, a stronger immune response does not necessarily mean better protection against actually getting the flu,” Dr. Choudhury notes.

Another study is expected to directly compare clinical outcomes between mFlusiva and a high-dose flu vaccine in adults 65 and older.

Is mFlusiva safe? What are the side effects?

Clinical trials so far suggest mFlusiva has a safety profile similar to traditional flu vaccines for serious adverse events. These are harmful or unexpected medical problems or side effects.

In a trial comparing mFlusiva with a standard-dose flu vaccine, serious vaccine-related adverse events were very rare. They occurred at similar rates in both groups.

Researchers also looked closely at heart-related events because of concerns previously raised about mRNA COVID-19 vaccines.

One participant who received mFlusiva developed cardiomyopathy and pericarditis. These are two heart-related conditions. This happened about three months later. It was unclear whether the vaccine caused them. One participant in the traditional flu vaccine group also developed pericarditis.

Dr. Choudhury says current data do not show a higher risk of these events with mFlusiva than with traditional flu vaccines.

The main difference so far is short-term side effects. Injection-site reactions, headaches, body aches, and fatigue occurred more often with mFlusiva than with traditional flu vaccines. This was seen across multiple studies.

“These symptoms are generally relatively mild, they go away on their own without any sort of treatment,” Dr. Choudhury says.

What are the advantages of an mRNA flu vaccine?

“The advantages are less so in how the vaccine itself works, and more so in how the vaccine is made,” Dr. Choudhury says.

Each year, scientists must predict which influenza strains will circulate months before flu season. Traditional flu vaccines take several months to produce. That can make it hard to change the vaccine if the strains that circulate are different from those expected.

Because mRNA vaccines do not rely on growing influenza virus in a lab, they can be produced more quickly. Dr. Choudhury says this could give vaccine makers more flexibility. They can update an mRNA vaccine when an unexpected flu strain begins circulating.

That flexibility could help produce flu vaccines that more closely match the strains actually circulating. It could also potentially improve how well seasonal flu vaccines protect people.

Who can get mFlusiva, and who may want to consider it?

mFlusiva is approved for adults age 50 and older. Based on the evidence so far, Dr. Choudhury says adults ages 50 to 64 may have the clearest reason to consider it.

People ages 50 to 64 typically receive a standard-dose flu vaccine. That was the same type used in the clinical trial. The trial found a lower rate of influenza among mFlusiva recipients.

Dr. Choudhury says mFlusiva may be especially worth considering for adults ages 50 to 64 with long-lasting (chronic) health conditions. These conditions can raise the risk of severe influenza. They include high blood pressure (hypertension), diabetes, chronic kidney or liver disease, obesity, or chronic lung disease.

Adults 65 and older can also receive mFlusiva. However, researchers are still gathering stronger clinical evidence. The studies compare mFlusiva with the high-dose or adjuvanted flu vaccines typically recommended for this age group.

Still, choosing between vaccines should not stop you from getting vaccinated.

“Ultimately, the best flu vaccine is the flu vaccine that you can get,” Dr. Choudhury says. If mFlusiva is not easy to get, she recommends getting an appropriate flu vaccine from your doctor’s office, pharmacy, or workplace rather than going without vaccination.

Can an mRNA flu vaccine change your DNA?

No. The mRNA in mFlusiva cannot change your DNA. It also cannot become part of your genetic code.

Dr. Choudhury says this has confused some people. Some worry that mRNA could reprogram their genetic code. But that’s not how the technology works.

Like other mRNA vaccines, mFlusiva gives cells temporary instructions to make a specific protein. Here, that protein is an influenza surface protein. The mRNA is then quickly broken down by the body.

“The mRNA in mFlusiva cannot become part of your genome,” says Dr. Choudhury.

When should you get your flu shot?

Flu season typically begins around October. Infections often peak around December. But the timing can vary from year to year.

Your immune system needs about two weeks after vaccination to build protection. Dr. Choudhury recommends planning ahead. The same timing applies to mFlusiva.

“I typically get the flu vaccine myself around early October,” Dr. Choudhury says.

Getting vaccinated is important even if you don’t consider yourself at high risk for serious problems from the flu. Influenza can cause severe illness that requires a hospital stay. Even a less serious case can leave you sick in bed for a week or longer.

“Getting your flu shot is a very easy, safe and effective step you can take to reduce your risk of getting sick and reduce your risk of making others sick,” Dr. Choudhury says.

Have questions about the new vaccine? Talk with your doctor.

Is it Time to Take My Child to the Doctor?

Updated on Jan 7, 2026 | Children's Health, Cold and Flu, Your Health

There are times during the cold and flu season when everyone seems to have the sniffles. While you may be tempted to book an appointment with a pediatrician at the sight of a runny nose, several symptoms can be managed with at-home remedies and over-the-counter medications.

Noha Basouny, MD, a pediatrician at Mount Sinai Doctors-Brooklyn Heights, explains what can be done at home, when you need to see the doctor, and how best to protect your child.

Help, my child is sick! What can I do about it?

First off, don’t panic. Many symptoms can be managed or treated at home without taking a trip to the pediatrician.

If your child has nasal congestion with or without cough, try using saline drops or nasal spray along with a humidifier or steam from the shower or bath. The humid and moist air along with the saline help to loosen congestion and allow mucus to drain. For children not old enough to blow their nose, use a nasal aspirator or bulb suction to clear away the mucus.

Should I use over-the-counter medications?

Forgo traditional “cough and cold” medicines as studies show they are neither effective nor safe, especially in children under six years old. Additionally, ingredients in many of these combination medicines overlap, putting children at greater risk for overdosing. If your child has a cough, honey is a helpful soother, although it is not safe in infants under one year.

Fever can be treated with acetaminophen for any child older than two months and ibuprofen for any child older than six months. Be sure to check the medication’s label—or consult a pediatrician—as dosing will depend on your child’s weight.

What is considered a fever? When should I be concerned?

A fever is defined as a temperature of 100.4°F or higher. It is helpful to know your child’s exact temperature as the trend of temperatures can help indicate whether the illness is improving or worsening.

Be sure to accurately check your child’s temperature. Remember, feeling his or her forehead with your hand will not give a sufficient measurement. A rectal temperature should be done for any baby six months of age and under. Rectal thermometers provide the most accurate temperature until age five; however, after six months it is okay to use a forehead (temporal) or ear (tympanic) thermometer. Oral thermometers should only be used after age five.

Seek medical help immediately if your child has a fever above 104°F or one that does not respond to fever-reducing medication.

When does my child need to see the doctor?

If your baby is under two months old and has a fever, they need to be taken to the emergency room. A fever in babies this young is taken very seriously and needs an evaluation that goes past what a doctor can do in the office. Between two and three months old, a baby with a fever should always be seen, but can first be evaluated by a pediatrician rather than going directly to the emergency room. For older babies and children, a fever lasting two days or more should be checked by the doctor.

In addition, although congestion and cough do not always need to be seen in the office, any child with difficulty breathing as well as these symptoms needs to be checked.

When in doubt, it is best to have your child checked by the doctor. Call your pediatrician if there are ever any questions about when to come in.

How can I prevent my child from getting sick?

The best way to protect your child from illness is to keep up to date on immunizations, including the annual influenza vaccine. While immunizations do not prevent all childhood illnesses, they protect against many serious infections as well as the dangerous complications that may arise from some of these infections.

Frequent hand washing, either with soap and water or with an alcohol-based hand sanitizer, is also an important way to prevent illness. When washing with soap and water, scrub for at least 20 seconds and rinse soap fully.

Finally, if your child is in school, preschool, or daycare, please keep them home if they are sick. Coughing, sneezing, and runny noses can linger from an illness so it is not imperative that these symptoms be fully resolved before returning to activities. However, children should be fever-free for 24 hours and back to their usual energy and activity level before returning to school. This will prevent further spread of illness in their classroom.

Noha Basouny, MD

Pediatrician, Mount Sinai Doctors Brooklyn Heights

Make an appointment with Dr. Basouny

Learn more about Children's Health at Mount Sinai

Is It Worth It to Take Tamiflu?

Nov 2, 2022 | Cold and Flu, Your Health

The peak season for the flu in the United States typically runs from December through March, according to the U.S. Centers for Disease Control and Prevention.

If you have not already gotten your annual flu shot, now is the time to do so. You can go to a Mount Sinai urgent care center for flu shots. Mount Sinai offers testing and treatment for those who show symptoms or have been exposed to the flu.

If you already caught the flu, there are ways to reduce its effects, such as taking antiviral medications like Tamiflu. However, managing the illness can be complicated, as some medical providers advocate the use of antiviral medications, while others treat flu symptoms and prescribe rest.

Joseph Feldman, MD

As an urgent care physician, Joseph Feldman, MD, Medical Director of Mount Sinai Doctors-Urgent Care, sees many patients with flu-like symptoms who have questions about how to treat their illness. In this Q & A, Dr. Feldman, Professor of Emergency Medicine at the Icahn School of Medicine at Mount Sinai, weighs the pros and cons of the ubiquitous antiviral medication and provides insight on how to best manage the flu so that you and your loved ones are healthy this flu season.

What is Tamiflu and when is it used?

Oseltamivir, also known as Tamiflu, is one of the more well-known antiviral medications that can be used to treat or prevent influenza. It is approved for use in adults, pregnant women, and children as young as two weeks of age. For patients who are otherwise healthy and who present with flu-like symptoms—these include painful body aches and fever coupled with sore throat, cough, congestion, headache, or even an upset stomach—Tamiflu may be an appropriate choice. If taken within 48 hours from the start of symptoms, it may provide some benefit by reducing the amount of time you feel sick.

Tamiflu can also be taken to help prevent the flu. If you or your child has been in close contact with someone who was recently diagnosed with influenza, it might be recommended to take Tamiflu—especially if you did not get the flu vaccine this year.

How effective is Tamiflu?

Unfortunately, the effectiveness of Tamiflu is marginal, as it cannot “cure” the illness. Most studies have shown that the medication will reduce the length of symptoms by only 12 to 24 hours, and if started after two days of symptoms, it does not help at all.

It is important to keep effectiveness in mind, as expectations for Tamiflu are often very high and, frankly, overhyped. The drug is usually taken for five to seven days and, if paying out of pocket, can cost more than $100. It can be challenging to find as it is often out of stock at multiple pharmacies given the high demand. Additionally, as with any medication, Tamiflu has potential side effects which may bring more harm than good. The most common of these are nausea, vomiting, and headaches that could exacerbate pre-existing conditions or lead to worsening dehydration. Other side effects, such as a severe allergic reaction, confusion, abnormal behavior, seizures, and life-threatening rashes, can occur but are extremely rare.

So, do I need the medication?

Maybe. The U.S. Centers for Disease Control and Prevention and the Infectious Disease Society of America recommend Tamiflu for patients who have a higher risk of developing complications such as pneumonia that may follow influenza.

These “at risk” patients include:

Those who are hospitalized
Pregnant women
Morbidly obese patients
Children less than five years of age
Adults older than 65 years of age
Patients with chronic heart, neurologic, or respiratory conditions such as asthma or stroke
Patients with immunosuppressing conditions such as HIV
Transplant recipients or those with diabetes and/or sickle cell disease

If you or your child fall within any of these categories, it is likely beneficial to take Tamiflu if you test positive for influenza. If you have been exposed to the flu by a close contact and have any of the previously mentioned conditions, it is also recommended that you start Tamiflu to help prevent getting sick.

For those who do not fall into a high-risk category, the decision to take Tamiflu should be made in conjunction with your health care provider. There are many times when it may not be worth the cost and the potential side effects.

Find a Mount Sinai Doctor

At Mount Sinai Urgent Care, we are always available to answer any questions so that you can make the most informed decision for yourself and your family.You can walk in without an appointment during our convenient daytime, evening, and weekend hours. We accept most insurance providers.

Visit a Mount Sinai Urgent Care location

Will Using A Steroid-Based Nasal Spray Increase My COVID-19 Risk?

Updated on Jun 30, 2022 | Allergy, Cold and Flu, COVID-19, Ear Nose Throat, Health Hub, Your Health

The Centers for Disease Control and Prevention considers those who are actively being treated with high-dose corticosteroids to be immunocompromised. Most nasal sprays for allergies do not fall into this category. Consult your primary care physician regarding the specific medication you are taking.

Allergy sufferers are hyperaware of every cough, sneeze, and sniffle entering the height of this allergy season. Those with allergies are not only concerned with distinguishing their allergy symptoms from the novel coronavirus that causes COVID-19, but many are now worried that the medications they take to manage their symptoms might put them at increased risk.

Steroid-based nasal sprays have come under particular scrutiny because the active ingredient—corticosteroids—can reduce the strength of the body’s immune system, which is concerning during a pandemic. Fortunately, nasal spray users need not worry. Anthony Del Signore, MD, PharmD, Director of Rhinology and Endoscopic Skull Base Surgery at Mount Sinai Downtown-Union Square, explains why allergy sufferers should keep using their medications.

Should I stop using my steroid-based nasal spray?

If patients are getting the relief that they usually receive from taking these medications, I typically say to continue using them. Often, symptoms of nasal drainage, nasal obstruction, or sinus infections will increase if you come off of the medications.

It is also important to remember that with topical intranasal sprays, as well as topical nasal rinses with steroids in them, the absorption of the steroid is quite low. And, there is conflicting evidence as to whether or not steroids taken this way will actually cause any decreased defense against the virus.

A lot of the data and recommendations that we’re getting is for systemic steroids, which are steroids taken by mouth or administered intravenously. That’s where we are seeing the decrease in the immune system.

As a result, I am staying away from prescribing oral steroids for the time being. But topical nasal sprays, as well as topical rinses, I’m okay with.

I take an allergy pill. Are there steroids in my medication?

We do not typically give oral steroids to patients complaining about the typical symptoms of seasonal allergies. Instead, we recommend nasal rinses/netipot, oral antihistamines, and intranasal antihistamines as well as intranasal steroids, with pretty good effect and results.

Oral steroids are usually reserved for more serious conditions like asthma, lupus, or severe systemic allergic reactions. And, if you have a more serious condition that requires the use of these oral steroids, you have to weigh the risks and the benefits. I would counsel these patients to practice social distancing, good hygiene, and taking other precautions. These preventative measures can often tip the scale so that the benefits outweigh the risk of the steroids.

What should patients do if they are concerned that their medications will decrease their ability to fight off COVID-19?

There’s a lot of information out there, and patients may be having a tough time finding the right answers. If patients have any questions during these tumultuous times, they should consider setting up an in-person or telemedicine appointment to talk with their health care provider. After getting a global view of the patient and seeing what other risk factors they have, proper recommendations can be made that may at least help to put fears at ease at a time that’s very uncertain for many.

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What Parents Should Know About the Novel Coronavirus and the Flu

Mar 4, 2020 | Cold and Flu, COVID-19, Your Health

The outbreak of a viral infection known as COVID-19, caused by a newly discovered coronavirus, is dominating the news, and governments, public health experts, and doctors are preparing for a growing number of cases around the world and in the United States.

The possibility of a coronavirus outbreak in the New York region, as well as the seasonal outbreak of the flu, pose special concerns for children. “There is a lot of anxiety out there and a lot we don’t know,” says Roberto Posada, MD, a pediatric infectious disease specialist in the Jack and Lucy Clark Department of Pediatrics at Mount Sinai Kravis Children’s Hospital and an Associate Professor of Infectious Diseases, and Medical Education, at the Icahn School of Medicine at Mount Sinai. “Fortunately we are learning from cases in China that most children don’t seem to get very sick from the coronavirus. But we also know that youngsters are one of the ways that viruses travel from one household to another.”

In this Q&A, Dr. Posada offers some basic advice for parents in the New York area.

What general advice do you have for parents who may be worried about their children?

The most important prevention strategy is to get your flu vaccinations. It’s not too late, and every child should be vaccinated every year. We are still seeing a lot of cases of the flu in the community, and some of these children need to be hospitalized. With all viruses in general and with respiratory-borne illnesses, everyone should wash hands frequently, with soap and water or with an alcohol-based sanitizer—especially before eating, after blowing your nose, and after entering your home from the outside. There is no difference between soap and water and a hand sanitizer when it comes to most viruses. Soap and water is preferable for eliminating gastrointestinal pathogens—infectious agents like viruses and bacteria that cause disease in your digestive tract—so that’s best after using the bathroom.

Also, teach children the proper etiquette for coughing or sneezing. They should use the inside of their elbow or blow into a tissue, and then wash their hands.

Are kids more at risk from viral outbreaks generally?

Kids tend to get more viral infections than adults, partly because their immune systems are not fully developed. How sick they can get depends on their age. Kids less than two years old are at higher risk for many infections like the flu.

How much of a risk does the coronavirus present for children?

We know from the data so far that the coronavirus seems to result in a very mild infection for children. Most of the patients that have been hospitalized or have died are older adults. Also, it is important to note that about 80 percent of people who have gotten the coronavirus experienced a very mild illness and did not need to be hospitalized. Unfortunately, about 20 percent of infected people develop more significant disease, and about 1 to 2 percent of all of those infected have died, again most of them older adults.

Should parents keep children out of public spaces, maybe off the subway?

At this time, I would suggest people in the United States go about life as normal, so long as they are washing their hands frequently. For example, if you take the subway or public transportation, or if you have been around people who are coughing or sneezing, it’s a good idea to wash your hands. Avoid as much as practical being in close proximity to people who are sick. You should also follow the news, as the recommendations from public health officials may change rapidly depending upon the cases we see. As always, the Centers for Disease Control and Prevention (CDC) and your local health department are the best sources of information.

The CDC recently said that if a widespread outbreak occurred in the United States, schools could be closed. Why is that an effective step?

If public health officials see the virus is spreading fast, and believe schools may be playing a role in facilitating the spread of the illness from household to household, closing of schools may be warranted.

How do children help transmit viral infections?

What happens with the flu or any virus is that young children pass them to their classmates. Young people are in such close contact with each other, especially if they are at day care, and it’s not uncommon for their saliva or mucus to mingle. They share toys, maybe even eating utensils. When kids get sick with an infection, they can pass the causative virus or bacteria along to other kids, and those kids then can bring it to their parents. That is how an illness crosses from one household to another and contributes to the spread of the viral infection.

Should we wear face masks?

At this point we are not recommending you or your children wear face masks to avoid getting sick. Face masks are mostly for health care workers who are in close proximity with people who are sick. And it can be helpful if someone who is already sick wears a face mask when in public spaces to prevent infecting others.

When should parents call the pediatrician if their child is sick?

My recommendations for the flu and other viral infections is the same as for illnesses in general. If your child’s symptoms are mild and in the respiratory tract, like a runny nose and sneezing, and if they are continuing with their other normal activities and these symptoms have lasted less than 24 hours, I would not worry or call. But if symptoms last more than 24 hours, if children also have a cough and fever, if they are not eating or drinking enough, and if they are disinterested in normal activities and look tired or sleepy, I would call your pediatrician. And let your pediatrician know if there is any history of travel or interactions with people who have been sick.

How Important Is Getting the Flu Shot?

Updated on Jun 30, 2022 | Cold and Flu, Infectious Diseases, Your Health

Despite all the media attention about the novel coronavirus, now known as COVID-19, influenza is currently a much bigger risk for most people in the United States. Yet many people do not plan to get a flu shot this year. You may be busy, or perhaps you think you might get sick from the shot, or that it’s not necessary. Matthew Weissman, MD, MBA, a primary care doctor with the Mount Sinai Health System, explains why you shouldn’t put it off.

Why should I get the flu shot?

The flu shot is extremely important. It not only prevents you from getting sick from flu, but it can lessen the severity of flu even if it’s not a perfect match for the type that is going around. For instance, my own daughter got the B strain of the flu. Luckily, she had a much milder case of it because she got the shot.

People forget that the flu is a deadly disease. Each season, tens of thousands of people die from the flu, and hundreds of thousands are hospitalized, according to the Centers for Disease Control and Prevention (CDC). Most of the people who died were not vaccinated. If you’re overweight, pregnant, elderly, or a child, or you have other diseases, you’re in a high-risk category. When you add all those up, you’re talking about a wide swath of New Yorkers.

Keep in mind that the flu shot doesn’t just protect you; it protects your co-workers, your classmates, your parents, and your grandparents—including people whose immune systems may not be good enough to build up their own defenses. It’s like a ripple effect, or herd immunity. It would be a great idea to have a workplace event for people to get vaccinated. It’s a smart idea for businesses to help cut down absenteeism this way.

Some people don’t get the shot because they think they’re going to feel sick for a couple days. Is that true or a myth?

People’s responses vary. Some people do feel a little feverish, get a sniffle, or have a sore arm for a bit. That’s actually a good sign, because it means their immune system is revving up to combat the flu. I think that’s a fair price to pay for not being incapacitated for over a week or being at risk of death from a vaccine-preventable illness. And these side effects don’t happen to everybody, and it doesn’t happen every time.

People have all kinds of excuses why they can’t get the flu shot. People are sometimes worried that the shot may cause a bad reaction because they have an egg allergy. But there are lots of ways to deal with that, including some vaccines that were not created using eggs. People should ask their doctor to find out what’s right for them.

Bottom line, the benefit of the flu vaccine outweighs the risk for most people, by far.

Is it too late to get a flu shot this season?

Definitely not. Flu season doesn’t appear to have peaked yet. The flu season is generally during fall and winter. The CDC recommends that everyone six months or older get the flu shot. You can get it any time up until spring, so don’t wait.

Matthew A. Weissman, MD, MBA, is Chair of Medicine at Mount Sinai Downtown and Associate Professor of Medicine (General Internal Medicine), and Pediatrics, at Icahn School of Medicine at Mount Sinai