What's the difference between cold and flu symptoms?

What people commonly refer to as “stomach flu” is actually a condition called viral gastroenteritis ⁸. Influenza (flu) and gastroenteritis (“stomach flu”) are different ⁹. Flu viruses affect the respiratory system, while the viruses that cause gastroenteritis affect the intestines ⁹. Flu viruses cannot cause “stomach flu”⁹.

Stomach flu symptoms include ⁹:

• Diarrhea
• Tummy pain or cramps
• Nausea or vomiting
• Fever (occasionally)

Some studies estimate that in healthy adults, the flu shot is 60% effective ¹⁰.

Although the flu vaccine is not 100% effective, it reduces the intensity of the symptoms and the time that you are ill ⁶. It also prevents hospitalization in ⁶:

• People with lung disease
• People with diabetes
• People with other chronic illnesses
• Adults older than 65
• Children
   

The flu shot may cause some side effects, which can resemble the symptoms of a flu ⁹. These flu-like symptoms are ¹⁰:

• Fever
• Muscle pain
• Joint pain
• Tiredness
• Headache
• Pain, redness, or swelling where the injection was made

Yes, it is possible for stress to cause some flu symptoms. However, the mechanisms by which this happens are not entirely clear ^{11, 12}. Some of the flu-like symptoms that stress can cause are

• Fever ¹¹
• Headache ¹¹
• Respiratory symptoms like shortness of breath ¹¹
• Other cold-like symptoms ¹²
   

Some research has found that people who have gone through majorly stressful life events are more vulnerable to developing a cold when they are exposed to a virus ¹². Your immune system is there to protect you, but stress may sometimes cause an inflammatory response that keeps your immune system from doing its job properly ¹².

For some people, stress-induced fever can go as high as 41°C (105.8°F) ¹¹.

Yes, many people who have the flu do not develop a fever ³. These are usually older people or those with weakened immune systems ‘³.

Fever is defined as a body temperature of 38°C (100.4°F) or above ¹³. High fever is 39.5°C (103.1°F) or higher, and very high fever is anything above 41°C (105.8°F) ¹³.

A high fever can be a cause for concern, and a very high fever can be dangerous ⁴.

Speak to your doctor if you are concerned about your fever, particularly about fever in your child ⁴. if your child has even mild fever but is 6 months or younger, you should speak to a medical professional ⁴.

You should also seek medical attention if ⁴:

• Your fever is over 40°C (104°F)
• You still have a fever after 3 days despite home remedies or treatments
• You are shivering and shaking uncontrollably
• Your condition is getting worse rather than better
• You have a severe headache
• You have any other unusual symptoms such as increased heart rate, hallucinations, vomiting, etc.