By Charlotte Hilton Andersen via Reader's Digest

We’re inundated with news about COVID-19 and other viruses, but how much do you really know about how they work and whom they target?


VIRAL SPREAD can be measured by R0, the average number of people someone with the virus will infect

THERE’S A LONG-STANDING ARGUMENT in scientific circles over how to classify viruses. They’re not inanimate, because they multiply, have genes, and evolve. Yet they’re not “alive,” as they don’t have cells, can’t convert food into energy, and can’t survive on their own. Viruses are biological zombies. They have one mission: to find a host and use it to replicate. They reproduce by hijacking the host’s cells, eventually causing them to burst and die. That’s why viruses that infect humans nearly always cause illness. Fortunately, just as we know a great deal about how viruses do their damage, so do we know how to fend them off. These facts are a good place to start.

1 There are many more viruses than you think. We often think of just a few viruses—influenza, HIV, and now coronaviruses—but they are the most plentiful microbes on the planet. There are about 320,000 types that infect mammals, but just 219 are known to infect humans, according to the U.S. National Library of Medicine.

2 They are even in the rain. The next time you dance in the rain or catch snowflakes on your tongue, you might want to consider the fact that it’s literally raining viruses. Viruses and other microorganisms get swept up into the atmosphere in small particles from soil and sea spray, returning to the earth via rain, snow, and sandstorms, according to a study published in Nature. Luckily, most of them aren’t infectious.


3 Figuring out how contagious they are is both an art and a science. One way to measure viral spread is R0 (pronounced “r naught”), which is the average of how many people may be infected by a single person with the virus. If the R0 is 4, then each infected person could spread the disease to about four others. The ideal R0 is less than 1, which means the virus is dying out in a population. But calculating R0 is far from straightforward, as it is based on biological, sociobehavioral, and environmental factors that can change rapidly.

4 You can get some viruses more than once. There’s a popular myth that once you’ve had a virus, you’re immune to it, but that’s not always the case, says Kathleen Dass, MD, an allergist and immunologist with Michigan Allergy, Asthma & Immunology Center in Oak Park. When you get a virus, your body builds up antibodies to fight it. Those antibodies stay in your system, helping you ward off future infections. (This is also how vaccines work.) However, not everyone makes enough antibodies, and they can wear off over time, which is why you need booster shots of some vaccines. In addition, viruses can mutate, making your antibodies ineffective against a new strain.

5 Viruses and bacteria may be hard to tell apart. It’s often difficult to tell based on symptoms whether an illness is caused by a virus or bacteria, but lab tests can confirm the culprit. Unlike viruses, bacteria are single-celled organisms that can live and reproduce on their own.

6 You can be contagious without ever showing symptoms. Some viruses, including those that cause herpes, COVID-19, and AIDS, can be spread via asymptomatic people (they never had signs of the illness) and presymptomatic people (they don’t have symptoms yet), according to the Centers for Disease Control and Prevention (CDC). Some people may even be “superspreaders,” infecting dozens to hundreds of other people without even realizing it. Take precautions to prevent spreading viruses even when you don’t feel sick.

7 You can be sued for knowingly spreading some viruses. While it’s unlikely anyone will take you to court for spreading the flu around the office (but please, stay home when you feel ill), you could be sued if you were to knowingly infect someone with an incurable virus, such as HIV or herpes. For instance, the singer Usher has been sued by sexual partners for not disclosing his herpes status. Similarly, actor Charlie Sheen has been sued twice for exposing women to HIV without telling them.

8 If you’re very overweight, you need to be extra cautious. Obese people are contagious with the flu virus 42 percent longer than those who aren’t obese, according to research in the Journal of Infectious Diseases. Because obesity is linked to many health problems, it may affect your immune system. Extra weight may make the flu shot less effective too.

9 The flu can trigger heart attacks. The influenza virus doesn’t just irritate your chest and sinuses—it also causes widespread inflammation throughout your body. That can increase the risk of developing blood clots that can trigger a heart attack, according to a study in the New England Journal of Medicine.

10 Cold air can make it easier to get sick. “Going out into the cold won’t make you sick on its own,” says Saralyn Mark, MD, president and CEO of SolaMed Solutions in Washington, DC. “But if you are in the cold often, your body adapts by allowing your mucous membranes to dry up. When that mucus dries up, it can’t protect you, and a virus can get in.”

11 Nail-biting is a no-no. Your fingers pick up germs easily, and chewing on them gives viruses a one-way ticket into your body. Cut your nails to keep them short and try to keep your fingers away from your nose and mouth.

12 Staying up late can slow your recovery. A study published in 2019 in the Journal of Experimental Medicine found that a good night’s sleep can boost the effectiveness of specialized immune cells called T cells. Sleep as much as possible when you’re sick to give your body a chance to recover.

13 Cold showers aren’t a fever cure. You may have been told by a parent or grandparent that an ice bath or a cold shower is a good way to lower a fever quickly, but cold water can cause shock and may end up spiking your temperature higher, says Patricia Whitley-Williams, MD, a professor and the chair of the department of pediatrics at Rutgers Robert Wood Johnson Medical School. Lukewarm water is best to help break a fever, she says.

14 Secondhand smoke increases your risk of getting sick. You already know that tobacco smoke—whether you’re the smoker or not—damages your lungs. That goes double when you’re sick because smoke weakens immunity and can make congestion and coughing worse.

15 COVID-19 isn’t a super-deadly plague. People hear the word pandemic and automatically think mass deaths, but most people who develop COVID-19 will recover, stresses Len Horovitz, MD, a pulmonary specialist at Lenox Hill Hospital in New York City. “Most people will get better at home on their own, but you can be in for a long course of illness that lasts several weeks,” he says. If you have chest pain, shortness of breath, or severe dehydration, go to the hospital.


16 Vitamin D might help. The relationship between COVID-19 and vitamin D isn’t entirely clear, but a recent analysis of preliminary research, published in Nutrients, found that having low levels of vitamin D is linked with more severe symptoms; increasing vitamin D levels may provide some protection by reducing your risk of getting infected with or dying from the coronavirus or the flu.

17 Yes, you should wear a mask. The CDC recently urged all Americans to wear cloth face coverings when in public to help prevent the spread of the coronavirus, but they can help lower the spread of other viruses as well. Wearing a mask doesn’t completely prevent you from getting sick, but if everyone wore them in public places, the rate of infections and community spread could be cut significantly, says Dr. Horovitz.

18 “COVID toes” are a thing. While it mainly produces respiratory symptoms, the virus that causes COVID-19 has been found to be capable of attacking most anywhere in your body, including your toes, explains Matthew G. Heinz, MD, a hospitalist and internist at Tucson Medical Center in Arizona. This symptom looks a lot like chilblains, which is redness, swelling, and itching of the toes (or fingers) in cold weather.

19 Loss of taste or smell is an early warning sign. Another unusual warning sign of COVID-19 is losing your sense of taste and smell, says Dr. Heinz. For some people with mild cases, this may be the only symptom, and it’s more likely to appear in younger people, he says. It’s not clear what causes it, but the disease provokes a profound inflammatory response throughout the body that could somehow impede the functioning of the senses.

20 COVID-19 can hurt your brain. A review of scientific literature published in June in the Annals of Neurology found that about half of hospitalized COVID-19 patients experienced neurological symptoms, including headaches, dizziness, difficulty concentrating, strokes, and seizures. Researchers speculate that this may be due to increased inflammation, lack of oxygen, an autoimmune reaction, or a clotting disorder triggered by the virus.


21 Herpes simplex virus might cause Alzheimer’s disease. Could a pesky little cold sore be responsible for destroying a person’s memory? Research over the past 20 years suggests a link between the herpes simplex virus (HSV-1), which causes cold sores, and Alzheimer’s disease. A Taiwanese study found that people with HSV infections had almost three times the risk of developing dementia later in life as those who were virus-free. Those who then took antiviral medication to treat their herpes cut their dementia risk by 90 percent.

22 Celiac disease might be caused by a virus. This autoimmune bowel condition affects an estimated 1 in 100 people worldwide, reports the Celiac Disease Foundation. New research published in Science suggests that it may be partly caused by the immune system’s response to a common virus called a reovirus.

23 Shingles could raise the risk for stroke and heart attack. A severe case of shingles, a disease caused by the varicella-zoster virus (the same one that causes chicken pox), can raise your risk for stroke, heart attack, and death. A meta-analysis of more than 20 years of research published in PLOS One found that even one case of shingles is associated with a significantly increased risk of brain and heart events.

Viruses are tenacious and can survive for quite a long time on surfaces outside the human body. Exactly how long they remain infectious depends on the type of surface and the environmental conditions; in a lab environment, the COVID-19 virus stayed active for two to three days on plastic and metal surfaces and for 24 hours on cardboard and paper, according to a study published in the New England Journal of Medicine.
Among the objects in your home that can harbor viruses:
✦ phones
✦ railings
✦ remotes
✦ keyboards
✦ faucets
✦ door and cabinet handles
✦ sheets, pillowcases, and blankets
In public places, be certain to clean your hands after touching:
✦ faucets
✦ door and escalator handles
✦ ATM and other keypads
✦ gas-pump handles
✦ weights at the gym
✦ utensils at buffets and salad bars

37 Ebola and Zika viruses can be transmitted sexually. You know that if you want to avoid sexually transmitted viruses such as herpes and HIV, you need to use protection when you have sex. But many other viruses can be transmitted through semen and/or vaginal fluids. In 2018, researchers discovered that the Zika virus could be transmitted sexually. A separate study found traces of the deadly Ebola virus in the semen of people who had recovered from it—up to two years after they were sick.

38 Zika virus might kill brain cancer. Not all virus side effects are bad. While the Zika virus can have devastating effects on fetal brains, its ability to target brain tissue may one day help it treat glioblastoma, a common type of brain cancer.

39 Rabies is the most deadly virus. Nearly 100 percent of people who get infected with the rabies virus will die from it, making it the most lethal known virus. To date, only 14 people have survived the disease after showing symptoms. The disease is also nearly 100 percent preventable with a vaccine, according to the CDC. If you get the vaccine before any exposure, it can prevent an infection, but it also works if you get the shots soon after being exposed. As most cases are caused by being bitten by an infected animal, it’s important to see your doctor after any animal bite, no matter how small.

40 If you can’t touch your chin to your chest, call your doc. A stiff, sore neck is one of the first signs of viral meningitis, a serious illness that may follow exposure to many common viruses, including enteroviruses and those that cause herpes, influenza, and measles. If you have cold- or flulike symptoms that progress to a severe headache, light sensitivity, lethargy, and a neck so stiff you can’t easily bend it forward, call your doc stat.

41 You can get rid of one virus with duct tape. Warts aren’t caused by cuddling with toads but rather by an infection with the human papillomavirus. The unsightly bumps are usually benign and will go away eventually on their own. One home remedy that may speed up the healing time is covering them with duct tape, according to a study published in JAMA Pediatrics. In fact, researchers found that duct tape therapy was significantly more effective than cryotherapy for the treatment of common warts.


42 Avoid the sun if you are prone to cold sores. Once you’ve had a herpes infection, the virus lies dormant in nerve cells in your skin and may reemerge as another cold sore in the same place as before, according to the U.S. National Library of Medicine. Recurrence often is triggered by sun exposure.

43 There is no cure for the flu and other viruses. Sad, but true. “The best ‘treatment’ is prevention through vaccines and lifestyle changes,” says Dr. Dass. “However, antiviral medications, such as oseltamivir [Tamiflu], can help you feel better faster, and they can make your symptoms less severe,” she says.

44 Don’t ask for antibiotics for your viral infection. Antibiotics kill bacteria, but they don’t work on viruses at all. Still, many doctors report feeling pressured to prescribe antibiotics by patients who insist on them despite having a viral infection, such as the flu, according to a study published in the Journal of the Royal Society of Medicine. In fact, the researchers found that so many people are convinced that antibiotics will help their viral symptoms that up to one third of all antibiotic prescriptions are unnecessary.

45 Soap and water really are the best defense. “Wash your hands” is practically a mantra these days, and for good reason. A drop of soap diluted in water literally pries apart the virus, causing the protein-wrapped particles to rupture and become useless. Make sure to wash for a minimum of 20 seconds and dry your hands on a clean towel. In public restrooms, avoid air dryers, which blow contaminants all over the place.

46 Disinfect your house regularly—but not with antibacterial wipes. Just as antibiotics don’t cure viral infections, antibacterial cleaners are ineffective against viruses, the CDC cautions. Worse, using antibacterial products can build antibiotic resistance. Instead, use hydrogen peroxide, ammonia, or another EPA-registered disinfectant product to clean items that may be contaminated with viruses, including the coronavirus. (See items 24–36 for more on that.)

47 Exercise can help you ward off the flu. Don’t skip that regular workout: “Regular exercise, which can include taking brisk walks, has been shown to improve your immune system, thus decreasing your likelihood of developing a cold or the flu,” Dr. Dass says. But don’t overdo it. “If you’re training for a long marathon, that can have the opposite effect and hurt your immune system,” she says.


48 Get a flu shot every year. One of the best ways to prevent the flu is to get a flu shot every year. (Some children may need two vaccines in one season.) There are over 200 strains of flu viruses, and they can mutate, which is why a new formula is created every season, says Jeremy Blais, PharmD, a pharmacist in Providence, Rhode Island, and a director at CVS Health. If you’re hesitant because of an egg allergy, there are two egg-free vaccines available—Flucelvax and Flublok.

49 Drink green tea. According to a meta-analysis published in Molecules, green tea may be an immune booster, helping fight both cold and influenza viruses. Researchers found that drinking green tea regularly not only helps you recover from a cold but may also help prevent recurring infections—and could make you less likely to get one in the first place.

50 Don’t count on herd immunity. You may have read that you can skip getting vaccinated if you live in a place where most people have had the disease or the vaccine, allowing you to take advantage of herd immunity. “But effective herd immunity requires that more than 90 percent of the population be vaccinated against a disease,” says Tish Davidson, medical writer and author of Vaccines: History, Science, and Issues and The Vaccine Debate. “The exact percentage depends on the contagiousness of the disease, and the flu is very contagious. With the current low flu vaccination rate, people should not count on herd immunity to protect them. It won’t.”