Symptoms and diagnosis

Flu and COVID-19

The symptoms of COVID-19 (coronavirus) are like flu symptoms. The main difference is that you usually do not have shortness of breath when you have the flu.

Get advice about symptoms of COVID-19 and what to do

Flu (influenza) is a severe infection caused by a virus. The flu virus infects your lungs and upper airways. 

Flu is unpredictable. If you are young and healthy, you will usually feel unwell for a week but, you will not need to see your GP. Most flu can be treated at home.

Antibiotics do not work on flu. Getting lots of rest and drinking plenty of liquids will make you feel better.

Most people who think they have the flu usually just have a cold.

The real flu tends to happen during the winter. It usually spreads between October and April.

Some people are at risk of the serious complications of flu.

People at risk of complications include:

  • people aged 65 and over
  • pregnant women
  • people with a long term medical condition
  • are a child aged 2 to 17

Read more about flu vaccine for children aged 2 to 17

You can see a list of other at-risk groups here.

If you have flu and you are at risk of the complications of flu, you should contact your GP. You may need special anti-viral medicines. These work best if started within 48 hours of flu symptoms.


Flu symptoms come on very quickly and you get  muscle aches and a high fever. Headache is very common. You will feel extremely weak and may find it hard to even get out of bed. After a few days, you may develop a cough. 

Flu symptoms can also include:

  • sore throat
  • difficulty sleeping
  • loss of appetite
  • diarrhoea or tummy pain
  • nausea and vomiting

The symptoms are similar for children. But they can also get pain in their ear and may be less active than usual.


It is useful to know the difference between a cold and the flu.

Flu symptoms:

  • come on suddenly
  • start with a fever, muscle aches, headache, weakness and fatigue

COVID-19 symptoms:

Symptoms of COVID-19 range from mild to severe.

Cold symptoms:

  • usually come on gradually
  • start with a sore throat and a blocked or a runny nose.

Symptoms of a cold are generally mild compared to flu.

Symptoms COVID-19 Flu Cold
Symptoms Fever or chills COVID-19 Common Flu Common Cold Rare
Symptoms Cough COVID-19 Common (usually dry) Flu Common (usually dry) Cold Mild
Symptoms Shortness of breath COVID-19 Common Flu No Cold No
Symptoms Lost or changed sense of smell or taste COVID-19 Common Flu Rare Cold Rare
Symptoms Fatigue COVID-19 Common Flu Common Cold Sometimes
Symptoms Aches and pains COVID-19 Common Flu Common Cold Common
Symptoms Sore throat COVID-19 Sometimes Flu Sometimes Cold Common
Symptoms Headaches COVID-19 Sometimes Flu Common Cold Rare
Symptoms Runny or stuffy nose COVID-19 Sometimes Flu Sometimes Cold Common
Symptoms Feeling sick or vomiting COVID-19 Rare Flu Sometimes Cold No
Symptoms Diarrhoea COVID-19 Rare Flu Sometimes in children Cold No
Symptoms Sneezing COVID-19 No Flu No Cold Common


For most people, flu is just a bad experience. But for others, it can lead to more serious illness. Some complications of flu can be life threatening.

If you are aged 65 years or older, pregnant, or if you have a long term medical condition are on medication, you have an increased risk of serious complications from the flu. You may need special anti-viral medicines. These work best if started within 48 hours of flu symptoms.

The most common complication is pneumonia. Other complications include bronchitis and ear infections.

Flu can also worsen existing conditions such as:

  • asthma
  • chronic obstructive pulmonary disease (COPD)
  • heart failure

Related topic

Vaccines needed during pregnancy - flu vaccine

Content supplied by the NHS and adapted for Ireland by the HSE

This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.