What Is It?
The flu, or influenza, is a viral disease of the respiratory tract—the nose, throat, bronchial tubes and lungs—and is highly contagious. A cold is a less severe viral infection, and often includes a runny nose, sneezing and coughing. Unlike flu, colds typically don't cause fever.
The flu, or influenza, is a viral disease of the respiratory tract—the nose, throat, bronchial tubes and lungs—and is highly contagious. It is spread though airborne droplets of moisture produced by coughs or sneezes. When you breathe these germs in through your nose or mouth, you may come down with the flu, generally within one to three days of exposure.
The flu is a potentially serious disease that can lead to hospitalization, or, in severe cases, death. Even healthy people can become very sick from the flu. Death rates from the flu vary from season to season. Flu-related death estimates have ranged from a low of 12,000 to a high of 56,000 from 2010 to 2014, according to the U.S. Centers for Disease Control and Prevention (CDC).
Outbreaks frequently start in school-age children, who carry the virus home and spread it to other groups.
And, beginning with the 2009-2010 flu season, there was a new flu to contend with—H1N1 flu ("swine flu"), which caused the first flu pandemic in more than 40 years. Since this outbreak, the seasonal flu vaccines have included coverage for the 2009 H1N1 flu. The seasonal trivalent flu vaccine usually contains one of each of the three kinds of influenza viruses that most commonly circulate among people today: influenza A (H1N1), influenza A (H3N2) and influenza B viruses. See the Prevention section for more information.
Flu seasons are unpredictable. There are some flu outbreaks every season, but it's impossible to predict the timing, severity and length of the flu season from year to year. Health officials say 2017-2018 was a bad season, with the highest number of flu-related hospitalizations ever recorded. The flu season in the United States commonly peaks in January or February, but it can begin as early as October and continue into May.
Because flu can be so serious and can spread so rapidly, the CDC recommends that everyone age 6 months and older get vaccinated every year. The nasal spray flu vaccine (FluMist Quadrivalent) is available this year after two years off market in the U.S. It is an option for non-pregnant people ages 2 through 49 years of age. The nasal spray is a four-component (quadrivalent) live attenuated influenza vaccine. Most regular egg-based flu shots also contain four strains of flu virus though there are three-strain (trivalent) options. Shots may or may not contain live strains, depending on what your health care professional recommends for you.
A yearly flu vaccine is the first and most important step in protecting against flu, according to the CDC.
Vaccines are especially important to those most susceptible to flu complications, including older people, children, pregnant women, people who are morbidly obese, people with compromised immune systems and those with chronic illnesses such as heart disease, kidney disease, asthma, COPD and diabetes. The most serious, often life-threatening complication of the flu is pneumonia. Other complications include ear infection, bronchitis, dehydration and worsening of chronic conditions, such as congestive heart failure, asthma or diabetes. Croup and a lung disease called bronchiolitis can also arise as complications in infants and young children.
In addition, the severity of illness is increased by exposure to cigarette smoke, which can injure airways and damage the cilia, the tiny hair-like structures that help keep airways clear. Toxic fumes, industrial smoke and other air pollutants are also risk factors.
There is also evidence that influenza can be more dangerous for women in their second or third trimester of pregnancy. The strain and stress of pregnancy on a woman's lungs, combined with the type of influenza, can lead to pulmonary problems, although there doesn't appear to be any danger to the fetus from the influenza virus itself.
There are three strains of the flu virus:
- Type A results in severe illness that easily spreads throughout a population, even globally, affecting a large number of people at the same time.
- Type B is a generally less severe strain that tends to affect fewer people.
- Type C causes very mild symptoms, so mild that many people don't even realize they're sick.
The influenza virus changes its genetic makeup every year. That's why you can get the flu every year and why a flu vaccine containing the new virus is recommended annually for everyone 6 months and older.
This constantly changing virus presents a particular challenge to medical science, making it impossible to create a single vaccine to prevent the disease. Instead, the World Health Organization (WHO) and the CDC monitor each new strain of influenza virus as it appears, assessing which may be the predominant virus in the following year's flu season. Scientists use this data, collected by a surveillance network, to develop a vaccine each year against the specific virus they predict will predominate. For the 2018-2019 season, the standard quadrivalent flu vaccine contains two influenza A viruses (H1N1 and H3N2) and two influenza B viruses.
Ask your health care professional for more information about restrictions and availability of flu vaccine or visit the CDC's website.
In terms of prevention and treatment, drugs called neuraminidase inhibitors (NAI)—also referred to as antivirals—attack influenza viruses, at the cellular level and block the viruses' ability to escape from cells already infected, thus preventing the infections from spreading.
These antiviral medications can also prevent the flu, which can help contain the virus in certain settings, such as family members passing the flu to one another in a household or coworkers spreading it in the workplace.