February 08, 2019
Influenza (flu) is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness. There are three types of influenza viruses: A, B and C.
Human influenza A and B viruses cause seasonal epidemics of disease almost every winter in the United States. The emergence of a new and very different influenza virus to infect people can cause an influenza pandemic.
Influenza type C infections cause a mild respiratory illness and are not thought to cause epidemic.
The flu is different from a cold. The flu usually comes on suddenly. People who have the flu often feel some or all of these symptoms:
Fever* or feeling feverish/chills
Runny or stuffy nose
Muscle or body aches
Some people may have vomiting and diarrhea, though this is more common in children
* It’s important to note that not everyone with flu will have a fever.
People with flu can spread it to others up to about 6 feet away. Most experts think that flu viruses are spread mainly by droplets made when people with flu cough, sneeze or talk. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs. Less often, a person might also get flu by touching a surface or object that has flu virus on it and then touching their own mouth or nose.
The best way to prevent the flu is by getting vaccinated each year.
Flu vaccines are designed to protect against the main flu viruses that research suggests will be the most common during the upcoming season. Three kinds of flu viruses commonly circulate among people today: influenza A (H1N1) viruses, influenza A (H3N2) viruses, and influenza B viruses.
What viruses will the 2018-2019 flu vaccines protect against?
There are many different flu viruses and they are constantly changing. The composition of U.S. flu vaccines is reviewed annually and updated as needed to match circulating flu viruses. Flu vaccines protect against the three or four viruses (depending on vaccine) that research suggests will be most common.
For 2018-2019, trivalent (three-component) vaccines are recommended to contain:
- A/Michigan/45/2015 (H1N1)pdm09-like virus
- A/Singapore/INFIMH-16-0019/2016 A(H3N2)-like virus (updated)
- B/Colorado/06/2017-like (Victoria lineage) virus (updated)
Quadrivalent (four-component) vaccines, which protect against a second lineage of B viruses, are recommended to contain:
- the three recommended viruses above, plus B/Phuket/3073/2013-like (Yamagata lineage) virus
When should I get vaccinated?
You should get a flu vaccine before flu begins spreading in your community. It takes about two weeks after vaccination for antibodies to develop in the body that protect against flu. The CDC recommends that people get a flu vaccine by the end of October.
Can I get vaccinated and still get the flu?
Yes. It’s possible to get sick with the flu even if you have been vaccinated (although you won’t know for sure unless you get a flu test). This is possible for the following reasons:
- You may be exposed to a flu virus shortly before getting vaccinated or during the period that it takes the body to gain protection after getting vaccinated. This exposure may result in you becoming ill with flu before the vaccine begins to protect you. (About 2 weeks after vaccination antibodies that provide protection develop in the body.)
- You may be exposed to a flu virus that is not included in the seasonal flu vaccine. There are many different flu viruses that circulate every year. The flu vaccine is made to protect against the three or four flu viruses that research suggests will be most common.
- Some people become infected with a flu virus the flu vaccine is designed to protect against, despite getting vaccinated. Protection provided by flu vaccination can vary widely, based in part on health and age factors of the person getting vaccinated.
What happens in the body when someone has the flu?
Influenza viruses usually infect the respiratory tract (i.e., the airways of the nose, throat and lungs). As the infection increases, the body’s immune system responds to fight the virus infection. This results in inflammation that can trigger respiratory symptoms such as cough and sore throat. The immune system response can also trigger fever and cause muscle or body aches. When infected persons cough, they can spread influenza viruses in respiratory droplets to someone next to them; persons can also become infected through contact with infectious secretions or contaminated surfaces. Most people who become sick will recover in a few days to less than two weeks but some people may become more severely ill. Following flu infection, pneumonia, secondary ear and sinus infections can occur.
Treatment with antivirals works best when begun within 48 hours of getting sick, but can still be beneficial when given later in the course of illness. Antiviral drugs are effective across all age and risk groups. However, most people with the flu have mild illness and do not need medical care or antiviral drugs. If you become sick with the flu, you should stay home and avoid contact with other people.
CDC recommends that you stay home for at least 24 hours after your fever is gone except to get medical care or other necessities.You should stay home from work, school, travel, shopping, social events, and public gatherings.
CDC also recommends that children and teenagers (anyone aged 18 years and younger) who have flu or are suspected to have flu should not be given Aspirin (acetylsalicylic acid) or any salicylate containing products (e.g. Pepto Bismol); this can cause a rare, very serious complication called Reye’s syndrome.
Stay away from others as much as possible to keep from infecting them. If you must leave home, for example to get medical care, wear a facemask if you have a cough and cover your mouth with a tissue. But most importantly,wash your hands often to keep from spreading the flu to others.