At least 20 million people, died in the 1918 influenza pandemic. You're especially at risk if you are an older adult, have diabetes, chronic cardiovascular or lung disease, or an impaired immune system.
But anyone can get influenza, a viral infection that attacks your respiratory system, including your nose, throat, bronchial tubes and lungs. Although other viral infections, especially colds and intestinal ailments such as gastroenteritis - a condition that causes diarrhea, nausea and vomiting - are often referred to as the flu, they're not. Real influenza usually doesn't affect your intestines. And while you may cough and sneeze with the flu, you're also likely to have a high fever, chills and body aches - signs and symptoms you won't typically have with a cold.
You're exposed to the flu when someone who's infected with the influenza virus coughs or sneezes, or you touch something they've handled. That's why the flu spreads rapidly anywhere people congregate - schools, child-care centers, offices, nursing homes, buses, even luxury cruise ships. Most outbreaks in North America occur between October and May. The peak season is usually late December to early March.
If you're at high risk of getting the flu, your first line of defense is an annual flu shot. For some people, antiviral medications taken within 24 to 48 hours of infection may help shorten the duration and intensity of symptoms slightly.
Signs and symptoms
The flu virus attacks your respiratory system. This leads to the symptoms you commonly experience with the flu. Some signs and symptoms, such as a runny nose, sneezing and sore throat, may seem like a common cold. But if you have a fever of 38 C or more, it's more likely you have influenza. Your fever may last from one day to as long as a week and, in some cases, may reach as high as 41 C.
You're also likely to feel worse with the flu than with a cold. Although you can probably carry on with a cold, the flu can knock you flat. Even after you've recovered, you may still feel tired.
Other signs and symptoms of influenza include:
The flu virus typically has an incubation period of one to four days, although symptoms usually come on suddenly. In most cases, you should feel better in about a week to 10 days unless you develop a serious post-flu lung infection, such as pneumonia or subacute bronchitis — an inflammation of the lining of your bronchial tubes.
The flu is caused by three types (strains) of viruses — influenza A, B and C. Type A is responsible for the deadly influenza pandemics (worldwide epidemics) that strike every 10 to 40 years, whereas type B causes smaller, more localized outbreaks. Type C is less common and causes only mild symptoms.
Type C is a fairly stable virus, but types A and B are constantly changing, with new strains appearing regularly. This results in a new epidemic every few years. Localized epidemics involving virulent strains of flu generally occur about every three to 15 years.
Once you've had the flu, you develop antibodies to the virus that caused it, but those antibodies won't protect you from new strains. And although outbreaks in different regions generally vary in their duration and severity, the fact that millions of people travel every day means that regional strains of flu can show up just about anywhere.
Children age 6 months to 2 years and people older than 50 are considered at high risk of complications from influenza. You're also at increased risk of influenza if you:
Children are at high risk if they:
The flu vaccine is safe for children 6 months or older. If your child isn't at risk of the flu but lives with someone who is — a grandparent, for instance, or anyone with a chronic heart or lung disease, or compromised immune system — you still may want to have your child vaccinated. That way, he or she is less likely to infect others. In fact, the more people who are immunized, the less likely it is that the infection will spread through a community.