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How long does the flu last for?

Medically reviewed by Last updated on Feb 8, 2023.

What causes the flu and how long does the flu last for? How does flu differ from stomach flu?

Official answer


A number of different viruses cause flu-like symptoms, so the length of time you have the flu for varies from person-to-person, depending on the cause. How bad your symptoms are, and how long you have them for, also depends on what other medical conditions you currently have or if you are pregnant, and how compromised your immune system is at the time of catching the flu.

Types of influenza

There are four main types of influenza viruses - A, B , C, and D. A and B are responsible for most cases of human flu during winter, type C generally causes a mild illness that is not very contagious, and type D viruses primarily affect cattle.

Type A and B flu viruses are the most common type to cause pandemics or epidemics. But even if two people have caught, for example, a type A influenza virus, symptoms may be mild in one person and severe enough to require hospitalization in another. Flu-associated deaths range each year from a low of about 3,000 to a high of about 49,000 people. Flu symptoms usually occur between one to four days after exposure to the virus and most people recover within a week, although you may feel tired or have a cough for much longer.

You should contact a doctor if you have another medical condition such as asthma, heart problems or diabetes and are finding it difficult to maintain good symptom control, or if your symptoms are severe. Be careful not to pass the flu on to those around you - the virus can be easily spread through sneezing or coughing or you may leave the virus on surfaces that you touch. Experts consider somebody with the flu infectious one day before symptoms begin and up to five to seven days after becoming sick. Some people may remain infectious for an even longer time. The best way to prevent the flu is to get a flu shot every year.

How long does a flu shot last for?

Only one year. This is because the viruses that cause flu are constantly changing. Most years the composition of the flu vaccine changes to reflect the Type A and Type B flu viruses that are currently in circulation. Typically, the flu vaccine includes two type A viruses and one or two type B viruses depending on the vaccine. Last year's flu vaccine may not contain the most current viruses.

Is the stomach flu more serious or does it last longer than the flu?

Stomach flu is a term used by many people to describe an illness of rapid onset with symptoms such as abdominal pain, nausea, vomiting, fever and/or diarrhea. The correct term is gastroenteritis.

Viral Gastroenteritis

Viruses are the most common cause of gastroenteritis; however, bacteria and even parasites can be responsible. Gastroenteritis is not usually caused by the same viruses that cause the flu (flu viruses tend to cause mainly respiratory problems), although sometimes children do get some vomiting or diarrhea with the flu.

In adults, noroviruses are the most common cause. Noroviruses commonly cause gastroenteritis outbreaks on cruise ships or in hospitals. Rotavirus is less common in adults but one of the most common causes of gastroenteritis in children. Rotavirus spreads easily so will often infect adults looking after children or those in shared accommodation. Other common viral causes of gastroenteritis include astrovirus and enteric adenovirus. The viruses that cause gastroenteritis are highly contagious and spread easily through direct contact with an infected person contaminated surfaces and food. Some even spread through contact with infected droplets released during coughing or sneezing.

Symptoms can take up to one to three days to develop and can last up to four to six days in young children, older adults or those with a compromised immune system. People with medical conditions such as diabetes may be particularly badly affected. Healthy adults may only experience symptoms for two to three days. Apart from electrolyte solutions to replace lost fluids and anti-diarrhea pills to relieve diarrhea, there is no drug treatment for viral gastroenteritis.

Bacterial Gastroenteritis

Bacteria such as E. coli, salmonella, campylobacter, and listeria are the main bacterial causes of gastroenteritis. The length of time a person remains sick for varies, depending on the infecting organism and their general health.


There are many different types of E.coli; E. coli O157: H7 is the worst type, causing bloody diarrhea and sometimes kidney failure and death. You can catch E.coli from contaminated food (particularly undercooked ground beef, unpasteurized milk, soft cheeses or juice, and raw fruits and vegetables such as sprouts). It may also be caught from animals, from drinking or swimming in contaminated water, or if you come into contact with the feces of an infected person. Symptoms usually come on within one to ten days and can last five to ten days. Most people recover within six to eight days. Rarely, some people may develop a severe complication associated with an E. coli infection, known as hemolytic uremic syndrome (HUS). Toxic substances form HUS destroy red blood cells and can cause kidney injury which requires intensive care, kidney dialysis, and transfusions.


Salmonella can also be spread through contaminated foods, particularly eggs, poultry, meat, and unpasteurized milk or juice, as well as through reptiles, birds, pet food and treats, and the bacteria can be killed by cooking and pasteurization. Symptoms usually last 4-7 days and most people recover without treatment. Older adults, infants, and people with other medical conditions may develop a more serious illness.


Campylobacter is spread through raw and undercooked chicken, unpasteurized milk and contaminated water. Symptoms may take from two to five days to develop and can last up to 10 days, although most people are only sick for a couple of days.


Listeria has the ability to grow in colder conditions so it is more commonly connected to refrigerated food. In many healthy people, it may cause relatively mild symptoms but it can be especially dangerous to unborn babies, older adults or people with weakened immune systems. Duration of illness is usually days to weeks.


Dehydration is the main issue to watch for with any case of gastroenteritis. If you or somebody you are caring for is unable to keep any fluids down without vomiting them back up, or if the person who is ill refuses to drink or is only drinking small amounts of fluids then you should seek urgent medical advice. Dehydration can come on suddenly and can be fatal in some people. Electrolyte solutions that have been specially formulated to replace glucose and electrolytes such as potassium and sodium lost through diarrhea or vomiting should be drunk instead of just water, as they are more effective at rehydration and reduce other symptoms such as tiredness or dizziness brought about because of an imbalance in electrolyte levels. Avoid sugary sports drinks; some of these may cause further dehydration.

Get plenty of rest and seek medical advice if your symptoms are severe.

How to avoid spreading gastroenteritis

Take care to avoid spreading gastroenteritis to other members of your household or people you come into contact with. People with gastroenteritis should not prepare, cook, or serve food to others until 24 hours after their symptoms abate. Remove any clothing or linen immediately that has been soiled with feces or vomit and wash separately from other items. Use a bleach-based household cleaner to clean and disinfect any surfaces contaminated by vomiting or diarrhea.

To lower your risk of catching gastroenteritis, always wash your hands for at least 20 seconds after using the bathroom, following contact with somebody who may be sick, and before eating.

  1. Norovirus (Norwalk Virus)
  2. Campylobacter. Food
  3. E. Coli. Food
  4. Listeria Food
  5. Seasonal Influenza: Flu Basics. Centers for Disease Control and Prevention.
  6. Key Facts About Influenza (Flu). Centers for Disease Control and Prevention.

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