Cold & Flu – Harvard Health

What is the difference between a cold and the flu?

While colds and the flu share some characteristics, there are also key differences.

Colds. The common cold (also called viral rhinitis) is an upper respiratory infection that may be caused by one of more than 200 viruses. The most common are rhinoviruses, which generate up to 40% of colds, most often in the early fall and spring. Other viruses that can trigger colds include adenoviruses, respiratory syncytial virus, and seasonal coronaviruses, which should not be confused with SARS-CoV-2, the coronavirus that causes COVID-19. Colds are most often transmitted by contact with germs from the nose and/or mouth via coughing, sneezing, or hand-to-hand contact. Although there is no cure for the common cold, some therapies can help treat and manage symptoms.

Flu. Influenza (known as the flu) is typically caused by either the influenza A or B virus. Most flu outbreaks occur during the winter. The influenza virus is quite contagious and is typically spread through the air or by direct contact with an infected person. Getting an annual flu vaccine at the beginning of flu season in October or November can reduce the chances of getting the flu and transmitting it to others.

Common cold: Symptoms and treatment

The common cold causes symptoms that affect the head and chest such as sore throat, stuffy or runny nose, sneezing, and nagging cough. Fatigue and general aches and pain are also common.

Symptoms typically peak on the second to fourth days of infection and last about one week. People are most infectious during the first 24 hours of the illness and usually remain contagious for as long as they have symptomst. Up to 25% of people may have persistent symptoms that last for several weeks.

Although there is no cure for the common cold, some therapies can help treat and manage symptoms. These include:

  • getting enough rest
  • drinking plenty of fluids
  • gargling with warm salt water to ease a sore throat
  • inhaling steam from a hot shower, vaporizer, or humidifier to help clear nasal congestion

Over-the-counter medications also can help manage cold symptoms. For example:

Pain. Acetaminophen (Tylenol) can relieve mild to moderate pain. Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen (Advil, Motrin) and naproxen sodium (Aleve) also help with pain and inflammation.

Congestion. Ingredients like pseudoephedrine (Sudafed, Advil Cold & Sinus, others), phenylephrine (Sudafed PE, Neo-Synephrine, others), and oxymetazoline nasal spray (Afrin) narrow swollen blood vessels in the nose to relieve congestion.
 
Cough and thick mucus. A cough isn’t always bad as it helps to loosen and remove excess mucus and phlegm causing chest congestion. But if a cough becomes bothersome or interferes with sleep, try a cough suppressant such as dextromethorphan (Triaminic Cold & Cough, others), an expectorant like guaifenesin (Mucinex, others), or combination medicines (Robitussin Maximum Strength, others). Cough suppressants stifle the urge to cough, while expectorants thin mucus in your airway to make it easier to remove.

Over-the-counter cold medicines that address more than one symptom are an option if you have multiple and/or severe symptoms.
Make sure to take only the recommended doses on the package.

Flu: Symptoms and treatment

Flu season typically begins in October or November and peaks between December and February. However, significant flu activity can last as late as May.

Flu symptoms and illness severity can vary depending on the virus type, a person’s age, and their overall health. Although it is a respiratory virus, the flu can affect other body systems and make you feel sick all over.

Common symptoms include:

  • moderate to high fever (101 to 103 degrees Fahrenheit)
  • chills
  • muscle and joint aches
  • headaches
  • fatigue
  • cough
  • sore throat
  • runny nose
  • diarrhea
  • dizziness  

Influenza symptoms usually last about four to five days but can range from  24 hours to a week or longer. As long as you have symptoms, you are contagious.

To ease symptoms, you can follow the same treatment protocol as the common cold: plenty of rest and fluids and taking over-the-counter medications to alleviate fever and pain, such as acetaminophen (Tylenol) and nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen (Advil, Motrin) and naproxen (Aleve).

In addition, antiviral medications can ease flu symptoms and shorten illness duration. These drugs include oseltamivir (Tamiflu), zanamivir (Relenza), baloxavir marboxil (XOFLUZA), and peramivir (Rapivab). These medications are available by prescription and must be started  within the first 36 hours of symptoms appearing.
 
Some people develop severe complications from the flu. Pneumonia is the most serious, but other complications include asthma attacks, ear infections, bronchitis, sinusitis, inflammation of the heart or other muscles, and inflammation of the nervous system. Notify your doctor if you experience:

  • chest pain
  • shortness of breath
  • ear pain
  • fever that does not go away after four days
  • a cough that produces blood or thick, foul-smelling mucus

Because many flu symptoms overlap with COVID-19 symptoms, people should get tested for COVID-19 either with an at-home test or at a pharmacy or doctor’s office.

Should I get a flu shot?

The single best way to prevent the flu is to get a flu vaccine (commonly known as a flu shot) each year. You can get the vaccine at your doctor’s office and at some workplaces, supermarkets, and drugstores. (For local vaccine locations, visit www.Vaccines.gov.)
 
The best time to get vaccinated is at the beginning of flu season in September or October. However, getting it in December or even later can still be beneficial since peak influenza activity can occur as late as February.
 
You must get a flu vaccine every year to be protected. The vaccine is modified annuallybased on the strains of the flu viruses that scientists anticipate will circulate that winter. Sometimes an unpredicted strain appears after the vaccine has been made. This is one reason you may still get the flu, even if you’ve been vaccinated. But if this happens, the disease is usually milder because the vaccine provides some protection.
 
The vaccine is made from an inactivated virus that can’t cause infection. In other words, the flu shot can’t give you the flu. About two weeks after you get vaccinated, your immune system develops proteins called antibodies that protect against infection from flu viruses. However, flu vaccines will not protect you from colds, COVID-19, or other flu-like illnesses caused by non-influenza viruses.
 
The flu vaccine can also be delivered via a nasal spray. The nasal vaccine contains weakened—not inactivated—virus, and may not be right for everyone.

In addition to the standard-dose flu shot, other available types of flu vaccines include:

  • The high-dose influenza vaccine, which is design edt for people ages 65 and older. It contains four times the dose of antigens found in the standard flu shot.
  • The adjuvant flu vaccine, which has an added ingredient that produces a stronger immune response in people ages 65 and older.

A flu vaccine’s most common side effects are soreness, redness, and swelling at the injection site. Other possible side effects include low-grade fever, fatigue, and aching muscles. These may begin six to 12 hours after vaccination and can last up to two days.
 
Children six months or older, teenagers, and adults should all be vaccinated. Vaccination is especially important for people at high risk for serious flu-related complications and those who live with or care for people at high risk, including:

  • children under age five, especially those under age two
  • children of any age on aspirin therapy
  • medical personnel
  • pregnant women and women planning to become pregnant during the flu season
  • people age 65 and older
  • people of any age with anemia, heart disease, diabetes, kidney disease, a compromised immune system, asthma, or other lung diseases
  • people who live in a nursing home or other long-term-care facility

Some people should consult a physician before being vaccinated. They include people who have had allergic reactions to the vaccine, have allergies to any of the vaccine ingredients like eggs, and those who have had Guillain-Barré syndrome, a disease in which the immune system attacks the nerves.

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