Seasonal Flu
- The seasonal flu is contagious and can cause mild to severe illness; and in some cases can lead to death. More…
- The timing and severity of this year’s flu season is uncertain. More…
- Type A and B flu viruses cause epidemics in the United States every year. More…
- The symptoms for the common cold and the seasonal flu are similar. More…
- Get vaccinated to protect yourself from the flu. If you do get sick, follow our treatment advice. More…
Seasonal Flu Basics
Influenza (the flu) is a contagious respiratory illness caused by influenza viruses. It spreads from person-to-person and can cause mild to severe illness; and in some cases, can lead to death.
- In the United States, yearly outbreaks of seasonal flu usually happen during the fall through early spring.
- The best way to prevent the flu is by getting a flu vaccination each year.
- Flu viruses can cause illness in people of any age group. Children are most likely to get sick because their immune systems aren’t strong enough to fight off the infection.
- Some groups are more likely to have complications from the seasonal flu. These include:
- those age 65 and older
- children younger than 2 years old
- people of any age who have chronic medical conditions (e.g. diabetes, asthma, congestive heart failure, lung disease)
- Complications from the flu can include:
- bacterial pneumonia
- ear or sinus infections
- dehydration
- worsening of chronic medical conditions
Every year in the United States, on average:
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The 2009-2010 Flu Season
Flu seasons are unpredictable in a number of ways, including the timing of the beginning, severity, and length of the flu season.
This flu season (2009-2010), there are more uncertainties than usual because of the emergence of a new 2009 H1N1 (Swine) flu virus.
Severity is uncertain. The 2009 H1N1 flu virus – along with regular seasonal viruses – will cause illness, hospital stays, and deaths this flu season in the United States. Scientists are concerned that the 2009 H1N1 virus may cause the season to be worse than a regular flu season – with a lot more people getting sick, being hospitalized and dying than during a regular flu season.
Timing is uncertain. In past years, seasonal flu activity typically did not reach its peak in the U.S. until January or February, but flu activity has occurred as late as May. However, the 2009 H1N1 flu virus caused illness, hospitalizations, and deaths in the U.S. during the summer months when influenza is very uncommon. So it is not known when flu activity will increase, when it will be most intense (peak), what viruses will circulate, or how long the season might last.
Flu Viruses
There are three types of flu viruses: A, B and C. The A and B viruses cause epidemics (widespread outbreaks in a country) of infection in people every year in the United States.
- Type C infections cause mild respiratory illness and are not thought to cause epidemics.
- Type A viruses are divided into subtypes. Subtypes of type A that have been found in people worldwide include H1N1, H1N2, and H3N2 viruses.
- Flu viruses are constantly changing. A global flu pandemic (worldwide outbreak) can happen if three conditions are met:
- A new subtype of type A virus is introduced into the human population.
- The virus causes serious illness in humans.
- The virus can spread easily from person-to-person in a sustained manner.
- The H1N1 Flu met all three conditions and caused a worldwide outbreak. In late spring, the WHO declared that a H1N1 flu pandemic is underway.
Flu Symptoms and Cold vs. Flu
Common Symptoms | Possible Symptoms |
| These symptoms may occur, but are more likely in children than adults:
Note that these additional symptoms may also be a sign of the H1N1 flu. |
Is it a Cold or the Flu?
Flu and the common cold are both respiratory illnesses, but they are caused by different viruses.
- Flu and the common cold have similar symptoms (e.g. fever, sore throat). It can be difficult to tell the difference between them.
- Your doctor can give you a flu test within the first few days of your illness to determine whether you have the flu.
- In general, the flu is worse than the common cold.
- Symptoms such as fever, body aches, extreme tiredness, and dry cough are more common and intense with the flu.
- Colds are usually milder than the flu. People with colds are more likely to have a runny or stuffy nose.
- Colds generally do not result in serious health problems, such as pneumonia, bacterial infections, or hospitalizations.
Seasonal Flu – Vaccination, Prevention and Treatment
- Vaccination is the best protection against contracting the flu. You need two vaccines to be fully protected this flu season, 2009-2010. The seasonal flu vaccine is different from the H1N1 flu vaccine. The CDC is encouraging people to get both vaccinations.More information on Vaccination
- Find a Flu Clinic Near You and Get Vaccinated. Visit the Flu Shot Locator on this site.
- For more prevention information, and to find out what to do if you get the flu, follow our advice for Prevention and Treatment
- Vaccine Selection for 2010-2011 Influenza Season
A key U.S. Food and Drug Administration Advisory Committee has recommended that protection against the 2009 H1N1 virus, which was first identified last April, be included in the 2010-2011 seasonal influenza vaccine starting this fall. That means that, barring some unforeseen circumstance, this fall, most Americans will be able to return to having one flu vaccine to protect them against the major circulating flu viruses. As is always the case with seasonal vaccine, younger children who have never had a seasonal vaccine will still need two doses.
| Seasonal Nasal (LAIV) | Seasonal Flu Shot |
H1N1 Nasal (LAIV)
| Minimum two weeks between vaccinations | May be given in same visit. |
H1N1 Flu Shot
| May be given in same visit. | May be given in same visit. |
