TDAP vaccine: When to get it, side effects, and safety
Influenza Spread: Airborne, Droplet, And Contact Transmission Explained
Influenza can be transmitted through the air by larger respiratory droplets and smaller aerosolized particles. It may also be spread through contact with contaminated surfaces. There are many ways to prevent getting sick with the flu.
Influenza viruses cause a respiratory illness that you may know more commonly as "the flu." In the United States, the Centers for Disease Control and Prevention (CDC) estimates that there were 35 to 65 million flu illnesses during the 2023 to 2024 flu season.
The flu is contagious, meaning that it can spread from person to person. But how is it spread? Is it airborne, or is it spread by other means, such as by droplets or contact? Keep reading below as we explore what to know about how influenza spreads.
So how exactly is influenza spread? Is it airborne, spread by droplets, or through contact? Why not all three?
Let's explore what we know about each type of transmission.
Respiratory droplets
According to the CDC, most experts believe that influenza viruses are mainly spread by respiratory droplets.
Respiratory droplets are made when you sneeze, cough, or talk. If respiratory droplets containing influenza virus come into contact with your mucus membranes, such as those in your nose or mouth, you can get sick.
Research suggests that respiratory droplets are on the larger side, typically greater than 5 micrometers (µm) in size. Due to this, they don't get very far and typically travel less than 6 feet before they fall out of the air the CDC reports.
That means you have to be pretty close to someone to contract the virus from them. However, respiratory droplets can fall onto various objects and surfaces, which leads us to our next method.
Contact
When respiratory droplets fall out of the air, they can land on nearby surfaces. Depending on the conditions, influenza virus can still be infectious for many hours.
For example, the virus can survive on hard, non-porous surfaces for 24 to 48 hours.
You can contract the virus if you touch a contaminated surface and then touch your nose or mouth.
Airborne transmission
When we talk about airborne transmission, we're generally referring to aerosolized particles containing influenza virus that are less than 5 µm in size. These types of particles can be made simply by breathing.
Unlike respiratory droplets (made when coughing or sneezing), which tend to land in the nose and throat, airborne particles can travel deeper into your respiratory tract. Because they are smaller, they can also remain suspended in the air for longer.
The CDC notes that airborne transmission of influenza virus can occur when you're in the vicinity of someone with the virus.
Indeed, a 2020 study notes that previous research has found that 42% to 63% of particles containing influenza virus are of this small, respirable size.
Further, researchers conducting a small 2018 study involving people with confirmed influenza and symptomatic were able to recover infectious virus from fine aerosols collected from breathing samples.
Overall, the exact contribution of the airborne route of influenza transmission remains unclear. While an older 2013 study estimated that the airborne route may account for half of all influenza transmission events, more research is needed.
The Environmental Protection Agency (EPA) notes that to be effective at removing viruses from the air, an air cleaner must be able to remove very small airborne particles, which it defines as those between 0.1 to 1 µm in size.
They recommend checking the product information provided by the manufacturer to verify that an air cleaner can remove particles of this size.
While air filtration can lower levels of virus in the air, it isn't a substitute for other preventive measures, such as avoiding contact with people who are sick, handwashing frequently, and cleaning high-touch surfaces.
The amount of time that influenza stays in the air can depend on the size of the particles that it's in.
For example, respiratory droplets between the sizes of 5 and 100 µm can remain in the air for about 5 minutes before dropping onto nearby surfaces.
Aerosolized, or airborne, particles can stay in the air for longer. This is particularly true if there's poor airflow or ventilation.
One 2015 study involved aerosolizing a laboratory strain of influenza and sampling the air. It found that after 60 to 90 minutes, levels of infectious virus in the air were still enough to cause an infection.
Aside from particle size, there are several other factors that can affect how long the influenza virus is infectious in the air or on surfaces. These include:
Yes and no. While the season doesn't directly cause an influenza infection, some winter climates can cause the influenza virus to spread more easily.
In many places the winter climate is colder and dryer, which can help the virus survive longer in the air and on surfaces. In addition, you're more likely to spend time in crowded indoor spaces with poor ventilation and less likely to be using sunscreen (although it's still important to).
This can create an ideal situation for influenza to spread across communities during the winter months.
According to the CDC, wearing a mask is an additional method for preventing the spread of respiratory viruses like influenza.
The protection goes both ways and can protect you and your community. If you currently have the flu, wearing a mask can help lower your risk of passing it to others. If you don't have the flu, a mask can prevent you from breathing in particles containing the virus.
A 2020 analysis of 21 studies found that masks had a protective effect against respiratory viruses, including influenza.
The authors of the analysis do point out that other studies have found that masks didn't have a significant effect on influenza transmission. However, these studies often did not account for mask type, fit, or whether they were used consistently and properly.
Yes. Hand hygiene, including using hand sanitizer, can significantly protect against influenza. Hand sanitizer can be particularly beneficial when soap and water are not readily available.
For example, one small 2019 study found that, compared to schools with no hand hygiene methods, those using hand sanitizer had a 53% lower incidence of laboratory-confirmed influenza infections.
Hand sanitizer can be used if soap and water are not available. Just be sure to use one that contains at least 60% alcohol, according to the CDC.
Influenza virus can spread in many different ways.
It can be transmitted through the air via respiratory droplets and airborne transmission. You can also contract the flu virus from contacting contaminated surfaces and then touching your nose or mouth.
There are many ways to prevent the flu. Some of these prevention methods we've discussed in detail here include practicing good hand hygiene, using an air filtration system, or wearing a mask.
Another great way to prevent contracting the flu virus is getting the seasonal flu vaccine. Receiving the flu vaccine each year can help prevent sickness and complications from the flu. If you do get sick, it can help reduce the length and severity of your illness.
Can The Flu Shot Give You Influenza?
The flu shot won't give you influenza because it contains inactive forms of the virus. However, you might have side effects like headaches, fevers, and sore muscles.
While some people think that getting a flu shot can give you the flu, this is a common misconception.
You might experience symptoms like a fever or muscle aches after getting a flu shot, but these are just side effects.
The flu shot is generally considered very safe for most people. If you've had a reaction to vaccinations in the past or aren't feeling well, it's a good idea to speak with your doctor before getting it.
Read on to learn more about how the flu shot works and possible side effects.
The flu shot — also called the influenza vaccine — works by introducing inactive flu viruses into your bloodstream.
This triggers the immune system to create antibodies, which are proteins that protect the body from infection.
Healthcare professionals give most flu shots with an injection, but you can also get a nasal spray alternative.
The flu shot can't give you influenza because it uses inactive viruses. However, you may experience side effects from the vaccine.
In some cases, you may catch the flu before your flu shot becomes fully effective. This doesn't mean your vaccine didn't work — it just means that it hadn't had enough time to develop antibodies that protect your body from infection.
You can also develop influenza in the future even if you have the flu shot. This is particularly common if you have a weakened immune response. You can also catch a different strand of flu than the ones you have been vaccinated against.
Common side effects from the flu shot include:
Side effects generally begin shortly after getting your flu shot and typically don't last more than a few days. It's important to mention any allergies and previous reactions with your doctor before getting a flu shot so they can discuss your options with you.
Getting a flu shot can help you avoid getting influenza. It can also stop you from spreading the flu to friends and loved ones.
If you do get influenza after getting a flu shot, it will likely be less severe.
Getting an influenza vaccine reduces the risk of going to the doctor with the flu by 40% to 60% and can reduce your risk of getting admitted to the intensive care unit (ICU) by 26% to 59%.
Flu vaccines can also help lower the risk of cardiac events in people with heart disease. It can also prevent worsening lung damage in people with chronic lung conditions.
In addition to the myth that the flu shot can give you influenza, there are many misconceptions about who can get a flu shot.
One common myth is that people with egg allergies can't get a flu shot. While you'll want to discuss this allergy and any previous vaccine reactions with your doctor, having an egg allergy doesn't you can't get a flu shot.
Another group who may believe they should avoid the flu shot are pregnant individuals. Getting a flu shot is actually advisable because it can protect both you and your growing baby.
How often should I get a flu shot?
Why do I feel sick after the flu shot?
Although you can't get influenza from a flu shot, you may feel a variety of side effects like headache, fever, muscle aches, or nausea. In rare cases, you may experience an allergic reaction to an ingredient in the vaccine.
Is it safe for me to get the flu shot?
The flu shot is considered safe with very few exceptions. People who should avoid the vaccine include babies under 6 months and those with life threatening allergic reactions to ingredients in the shot.
You may wish to talk with your doctor and delay getting your flu shot if you're feeling poorly.
A flu shot can't give you influenza. Instead, getting a flu shot can reduce the risk of you and your loved ones becoming seriously ill from influenza. You should get a flu shot every year unless your doctor recommends otherwise.
After a flu shot, you may experience side effects like a fever, headache, and muscle pain.
If you've had an allergic reaction to a flu shot in the past or aren't feeling well, it's a good idea to talk with your doctor before getting your flu shot.
They can help advise you on alternative flu vaccinations and whether you should delay getting your shot.
Flu Symptoms
Influenza, aka the flu, is a highly contagious virus that infects your nose, throat, and sometimes your lungs. You can get sick by being around someone with the flu when they cough, sneeze, or talk. That's because the virus travels through the air on tiny droplets of fluid. If flu germs land on a surface and you touch them, then touch your nose, eyes, or mouth, you can get sick.
Some people who get the flu have only mild symptoms. Others become severely ill and need to go to the hospital. The flu can also be fatal. Getting a flu shot every year can help protect you.
Here are the specific signs and symptoms of flu to look out for.
If you come down with the flu, home care like over-the-counter pain relief, lots of fluids, and rest is usually enough to help you recover. But in some cases, your doctor may also prescribe an antiviral medication. (Photo Credit: E+/Getty Images)
Every year, about 20 to 40 million people in the U.S. Get sick with the flu.
If you're one of them, you may think you have a cold at first. You could have a runny nose and a sore throat. But unlike a cold which gets slowly worse before it gets better, flu symptoms worsen very suddenly.
You'll likely start feeling sick 1 to 4 days after you come into contact with the virus.
If you have the flu, you could have some or all of these symptoms:
Vomiting and diarrhea aren't common flu symptoms in adults. They're more often seen in kids.
The symptoms of colds and flu can look a lot alike. Here's how to tell which condition is making you sick:
Fever. It can last 3 or 4 days with the flu; it's rare with a cold.
Aches. They might be severe with the flu; they're mild with a cold.
Chills. You're likely to have them with the flu, but they're rare with a cold.
Fatigue. This is common with the flu and happens sometimes with a cold.
Sneezing. You're more likely to have this with a cold than with the flu.
Cough and chest discomfort. This is common with both but tends to be severe with the flu.
Stuffy nose. This sometimes happens with the flu but is very common with a cold.
Sore throat. A scratchy, tender throat can happen with the flu but is more likely with a cold.
Headache. Your head is more likely to pound when you have the flu.
Generally speaking, cold symptoms are usually mild. Flu symptoms may become severe enough to lead to other health issues.
The flu and COVID are both upper respiratory infections, but they're not caused by the same type of germ. COVID is caused by a coronavirus known as SARS-CoV-2.
COVID spreads more easily than the flu and often causes more severe illness. You're also contagious for a longer period.
Without testing, it can be hard to tell whether you have COVID or the flu. They share many of the same symptoms. The exception is a loss of taste and smell for no reason (like having a stuffy nose) — which is common with COVID but rarely happens when you have the flu.
If you're sick with COVID, your symptoms can take longer to show up than the flu — about 2-14 days after you're exposed to the germ. Like a cold, COVID symptoms may also start out as mild, and then get worse over time.
If you think you have COVID and notice any of the following symptoms, it's important to go to the ER or call 911 right away:
If you do get sick, you'll need to take care of yourself. In most cases, the best things to do when you have the flu are:
Get lots of rest. When you're sick, your body needs more sleep to regulate your immune system.
Drink plenty of fluids. Sweating from a fever or chills, diarrhea, and vomiting can all put you at risk of getting dehydrated. While water is the best choice for staying hydrated, fluids such as tea, electrolyte drinks, broths, and soups are also good options. Warm fluids can help soothe your throat. Try to avoid sugary sodas and fruit juices as well as caffeinated drinks.
Apply heat on achy muscles. A heating pad or warm (not hot) shower or bath can provide some relief. But only try this if you aren't running a fever.
Turn on a humidifier. Adding more moisture in the air can ease a stuffy nose and help you cough less.
Avoid contact with other people. You don't want to spread your germs around. Stay home from work or school until you recover.
Try over-the-counter (OTC) pain relief. No one under the age of 18 should take aspirin. It raises your risk for a rare brain disease called Reye's syndrome. If you're not sure whether to take acetaminophen or a nonsteroidal anti-inflammatory drug (NSAID) such as ibuprofen, ask your doctor. Based on your symptoms, they can also suggest an OTC cough suppressant (which can reduce coughing) or expectorant (which helps get rid of mucus in your throat and lungs).
Flu medications
Antibiotics can't treat the flu. But if you're at risk of complications from the flu, your doctor might prescribe antiviral medication.
These types of drugs work best when you take them no more than 48 hours after your symptoms start. Antivirals can decrease how severe your symptoms are and reduce the time that you're sick. They may also help prevent serious health issues related to the flu.
Antiviral medications include:
Antivirals aren't supposed to replace a flu shot. Your best option is to try not to get the flu in the first place. The CDC recommends a yearly flu vaccine (as either a shot or a nose spray) for everyone 6 months or older. Studies show that past vaccines have been able to decrease the risk of flu by 40%-60%.
For most people, the flu is a short-term illness that runs its course in 5 to 7 days. If you've had a flu shot, you may start feeling better even sooner. But everyone is different. It may take you longer to feel back to your usual self. And some symptoms, such as fatigue, may persist longer than others.
If you're in pretty good health, you probably won't have serious problems from the flu. But many different things can raise you at risk for complications, including:
If you're Black, Hispanic, American Indian, or Alaska Native, you're also at higher risk of flu complications.
Flu complications can include:
If your symptoms are mild and you're not at risk for complications, you probably won't need to see your doctor. Taking care of yourself at home will probably be enough to recover from this illness.
But if you come down with the flu and are concerned, let your doctor know right away. They may prescribe antiviral medicine, give you specific advice to follow, and keep a closer eye on your health.
When to seek emergency care for flu symptoms
Whether or not you fall into a "high-risk" group, get medical help right away if you have any of the following:
The signs that your child needs emergency care include:
If you or your child have an ongoing medical condition, it's also a good idea to check in with your doctor. There may be other symptoms that signal you need to go to the ER.
Seasonal flu follows a pattern, starting in the fall and ending in the spring. The first sign is often a sudden rise in the number of school-age kids getting sick. This is usually followed soon after by illness in other groups, such as parents and caregivers.
The CDC advises getting a flu shot in October, around the beginning of flu season. That's because it will take 2 weeks to get into your system and fully protect you. The flu virus tends to peak in December and January. But you can be infected anytime, so it's never "too late" for a flu shot.
Self-care is usually enough to treat flu symptoms, but always call your doctor with concerns. The complications from flu can be severe and sometimes fatal. A flu shot can help protect your health by reducing how severe your symptoms are and how long they last.
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