These statistical estimations are based on CDC-measured flu hospitalization rates that are adjusted to produce an estimate of the total number of influenza infections in the United States for a given flu season.
The estimates for the number of infections are then divided by the census population to estimate the seasonal incidence or attack rate of influenza. Does seasonal incidence of influenza change based on the severity of flu season? The proportion of people who get sick from flu varies. You may be able to spread flu to someone else before you know you are sick, as well as while you are sick. The time from when a person is exposed and infected with flu to when symptoms begin is about 2 days, but can range from about 1 to 4 days.
Complications of flu can include bacterial pneumonia, ear infections, sinus infections and worsening of chronic medical conditions, such as congestive heart failure, asthma, or diabetes. Anyone can get flu even healthy people , and serious problems related to flu can happen at any age, but some people are at high risk of developing serious flu-related complications if they get sick. This includes people 65 years and older, people of any age with certain chronic medical conditions such as asthma, diabetes, or heart disease , pregnant women, and children younger than 5 years.
The first and most important step in preventing flu is to get a flu vaccine each year. Flu vaccine has been shown to reduce flu related illnesses and the risk of serious flu complications that can result in hospitalization or even death. CDC also recommends everyday preventive actions like staying away from people who are sick, covering coughs and sneezes and frequent handwashing to help slow the spread of germs that cause respiratory nose, throat, and lungs illnesses, like flu.
It is very difficult to distinguish flu from other viral or bacterial respiratory illnesses based on symptoms alone. There are tests available to diagnose flu. More information is available: Diagnosing Flu. You can inhale the droplets directly, or you can pick up the germs from an object — such as a telephone or computer keyboard — and then transfer them to your eyes, nose or mouth. People with the virus are likely contagious from about a day before symptoms appear until about five days after they start.
Children and people with weakened immune systems may be contagious for a slightly longer time. Influenza viruses are constantly changing, with new strains appearing regularly. If you've had influenza in the past, your body has already made antibodies to fight that specific strain of the virus. If future influenza viruses are similar to those you've encountered before, either by having the disease or by getting vaccinated, those antibodies may prevent infection or lessen its severity.
But antibody levels may decline over time. Also, antibodies against influenza viruses you've encountered in the past may not protect you from new influenza strains that can be very different viruses from what you had before. If you're young and healthy, the flu usually isn't serious. Although you may feel miserable while you have it, the flu usually goes away in a week or two with no lasting effects.
But children and adults at high risk may develop complications that may include:. Pneumonia is one of the most serious complications. For older adults and people with a chronic illness, pneumonia can be deadly. The flu vaccine can reduce your risk of the flu and its severity and lower the risk of having serious illness from the flu and needing to stay in the hospital.
Flu vaccination is especially important this season because the flu and coronavirus disease COVID cause similar symptoms. Preventing the flu and reducing the severity of flu illness and hospitalizations could also lessen the number of people needing to stay in the hospital.
This year's seasonal flu vaccine provides protection from the four influenza viruses that are expected to be the most common during the year's flu season. This year, the vaccine will be available as an injection and as a nasal spray. Avoid crowds. The flu spreads easily wherever people gather — in child care centers, schools, office buildings, auditoriums and public transportation.
By avoiding crowds during peak flu season, you reduce your chances of infection. Also avoid anyone who is sick. People with flu are most contagious in the first three to four days after their illness begins. Most healthy adults may be able to infect others beginning 1 day before symptoms develop and up to 5 to 7 days after becoming sick. Children and some people with weakened immune systems may pass the virus for longer than 7 days.
Symptoms can begin about 2 days but can range from 1 to 4 days after the virus enters the body. That means that you may be able to pass on the flu to someone else before you know you are sick, as well as while you are sick. Some people can be infected with a flu virus but have no symptoms. During this time, those people may still spread the virus to others. You may be able to pass on flu to someone else before you know you are sick, as well as while you are sick. When contaminated hands touch other objects, the virus is transferred to them.
Others have shown that infectious influenza virus may be persist on paper currency for several weeks. Influenza transmission can be reduced by covering your nose and mouth when coughing or sneezing, and by washing hands often with soap and water or alcohol-based hand cleaners. Note that CDC does not recommend the use of face masks for reducing viral spread.
It is important to recognize that, in human infections, maximum levels of virus shedding may occur about a day before the peak of symptoms. Ethical considerations preclude controlled influenza virus transmission studies in humans, and therefore animal models must be used. Ferrets are susceptible to many strains of influenza virus, and develop symptoms similar to those in humans. However these animals are costly and difficult to house, precluding their use in most large scale transmission studies.
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