How Viruses Spread: Understanding Transmission and Prevention

It’s understandable to feel anxious if you hear about a virus sweeping through the local elementary school or invading cruises like the one you’re taking next month. What can you do to keep yourself and your loved ones bug-free? To answer that question, it helps to know how different viruses spread.

Infectious disease expert Sherif Beniameen Mossad, MD, offers a crash course on the different modes of virus transmission and shares practical tips to keep you and your family safe.

Common ways viruses spread

There are a few basic ways that viruses can move from person to person — and each group of viruses has its own preferred route. Common ones include:

• Respiratory transmission: When we breathe, talk, cough or sneeze, we send tiny droplets into the air that can travel up to six feet. Those particles can carry certain viruses — like the ones that cause the common cold — to other people’s faces, hands and nearby surfaces. Some viruses, such as measles, can hang in the air for up to two hours or become “airborne,” infecting people as far as 100 feet away.
• Direct contact: Viruses, like herpes simplex and human papillomavirus (HPV), spread through direct physical contact with an infected person’s skin, mucous membranes or bodily fluids. In some cases, you can also catch them by touching sores, lesions or rashes.
• Indirect contact: This is when a virus makes a pitstop on a surface or object. “Imagine coughing into your hand and touching a table,” Dr. Mossad illustrates. “Some viruses can survive on that table long enough for someone else to pick them up. If that unlucky person then touches their eyes, nose or mouth before washing their hands, the virus can enter their body.”
• Fecal-oral transmission: Poop can carry certain viruses, like norovirus (stomach flu) and hepatitis A. Those viruses spread when contaminated poop particles get onto food, water, surfaces or unwashed hands — and end up in your mouth.
• Bloodborne transmission: Viruses, like human immunodeficiency virus (HIV), hepatitis B and C, spread when infected blood (or in some cases, other bodily fluids) enter your bloodstream. Depending on the virus, this may happen through sex, sharing needles, during pregnancy or childbirth, and more.
• Vector-borne transmission: Vector-borne viruses hitch rides on living organisms, like ticks, but typically don’t spread person-to-person, Dr. Mossad says. West Nile Virus, for example, travels via mosquito.

This list isn’t exhaustive, and there’s often overlap between categories. Many viruses have more than one mode of transmission. Depending on the virus you’re learning about, these broad labels can sometimes be more misleading than helpful.

For example, HIV is a bloodborne virus and it does spread through certain types of direct contact, such as unprotected sex or breastfeeding. But you can’t get it through casual contact, like hugging or kissing.

And while the Zika virus is mainly vector-borne, it can also spread through sex and from a pregnant woman to their fetus.

“If you’re not sure how a specific virus spreads or what precautions to take, ask your healthcare provider,” Dr. Mossad advises. “They can help you understand your risk and lay out your prevention options.”

Factors that influence how easily viruses spread

All viruses are built to spread, but they don’t all transmit at the same rate or with the same efficiency. Whether (and how easily) they make it to you depends on many factors, including:

• Virus type: If you look at different viruses under a microscope, you’ll notice that they have different shapes, sizes and structures. These and other qualities dictate how resilient they are, how they move and how well they stick to their target, Dr. Mossad says.
• How it spreads: Some transmission routes are more efficient than others. Viruses that transmit through droplets, like measles, are up to 10 times more contagious than bloodborne viruses, like Ebola.
• Incubation period: That’s the time between being exposed to a virus and having symptoms. “Incubation periods can last from hours to weeks, depending on the virus. In some cases, like chickenpox or influenza, you can spread the virus one to two days before becoming sick,” Dr. Mossad explains.
• Latency: Some viruses can stay in your body dormant for years, only to pop up again later. If you’ve had chickenpox, for example, the varicella-zoster virus is still in your body. It may never reactivate — but if it does, it comes back as shingles.
• Environmental conditions: Your surroundings can play a deciding role in how a virus survives — and how likely you are to catch it. Factors like cleanliness, weather patterns, population density and air quality are just a few to keep in mind.
• Your immune health: The stronger your body’s natural defenses, the less likely a virus is to take hold and make you sick.
• Behavior: Getting sick isn’t a choice. But things you do — like going to a sold-out concert or staying indoors with friends when it’s cold — can increase your chances of catching a virus.

How to reduce or prevent transmission

Dr. Mossad says that slowing the spread of viruses is a matter of making simple, everyday decisions, from scheduling your annual physical to practicing good cough hygiene.

“One of the best things you can do to break the transmission cycle is routinely washing your hands with soap and water or hand sanitizer, especially after using the bathroom or coughing, and before eating,” Dr. Mossad says.

You protect others when you scrub up, too, not just yourself. Viruses are tricky because they often spread before you even know you’re sick. That’s one of many reasons why healthcare workers are expected to wash their hands before and after seeing a patient, Dr. Mossad explains.

Even with lots of instruction and encouragement, little kids (and let’s be honest, plenty of adults) aren’t the best hand washers. Dr. Mossad recommends carrying hand sanitizer as a backup.

“It may not be as effective as handwashing, but it will do the trick when you aren’t near a sink,” he notes.

You bolster your and your family’s defenses against viruses even further when you:

• Avoid touching your face: “Your eyes, mouth and nostrils are like open doors for germs,” Dr. Mossad says. “Touching your face with unwashed hands gives viruses an easy way into your body.”
• Cover your cough or sneeze: Coughing or sneezing into your arm or the crook of your elbow is a good way to avoid sharing your respiratory droplets with other people.
• Clean high-touch surfaces: Did you know norovirus can live on surfaces for up to two weeks? That’s one of many reasons to regularly clean and disinfect surfaces with an antimicrobial that’s proven to kill stubborn germs.
• Get preventive care: When you get regular checkups, you improve the odds that your provider will spot medical conditions that affect your immune health.
• Consider vaccination: There are vaccines available for many viruses, including the flu, COVID-19, respiratory syncytial virus (RSV) and pneumonia.
• Protect your immune health: Mossad says that eating nutritious foods, exercising, staying hydrated, managing stress and getting plenty of sleep can help keep your defenses strong.
• Take extra precautions as needed: In crowded or high-risk settings, some people choose to wear a mask for added protection, especially if they’re more vulnerable to illness.

Nobody can avoid all viruses all the time. But understanding how they work, staying informed about the ones circulating in your area and taking these practical steps can help reduce your and your family’s chances of getting sick.