Type C is the mildest form of the flu. For most people, this usually only causes mild respiratory infections.[2]
Learn About Cold & Flu
What Types of Flu Are there?
Although you think of influenza as “the flu”, there are actually four types of influenza viruses.
How many types of flu are there?
There are three main types of flu viruses that affect humans (A, B and C). Although there is a type D flu, it only affects cattle1.
Human Influenza viruses of types A and B are the cause of the flu season every winter in the US, but A viruses are the only viruses known to cause flu pandemics1.
The different types of flu
What is type A flu?
Type A is typically thought to be more serious than Type B – and is known to cause serious outbreaks that can increase your risk of disease. It is characterized by subtypes and strains and they are always constantly changing from one season to the next. These types are naturally hosted by wild birds such as ducks, geese, shorebirds and some mammals and an example of this is swine flu.2
Type A flu viruses are divided into subtypes based on proteins of the surface of the virus. There are 18 hemagglutinin subtypes (H) and 11 types of neuraminidase subtypes (N). When you see H and N referring to a flu virus (eg. H1N1) this is what that means1.
What is type B flu?
Type B influenza is only found in humans – and people tend to see it as less severe than type A. This has been challenged in recent years however, and The Centers for Disease Control and Prevention reported that this could be equally as dangerous.2
B type flu viruses are divided into two lineages B/Yamagata and B/Victoria1.
What is type C flu?
Type C is the mildest form of the flu. For most people, this usually only causes mild respiratory infections.2
Type B influenza is only found in humans – and people tend to see it as less severe than type A. This has been challenged in recent years however, and The Centers for Disease Control and Prevention reported that this could be equally as dangerous.[2]
B type flu viruses are divided into two lineages B/Yamagata and B/Victoria [1].
What type of flu is the worst?
At one time, Type A was considered more serious than Type B. However, studies have found that both Influenza A and B could result in similar rates of illness and/or death.3 Type C is the mildest form of flu and usually shows similar symptoms to that of the common cold in adults.3
What types of virus are in the flu vaccine?
Each season’s flu vaccine contains two A type viruses and one or two B type viruses1. Because flu viruses change so much you need to top up every year to make sure that you are protected.
Read about symptoms of the flu
