【Flu Viruses】What Are the Differences Among 4 Flu Viruses

2022-12-08

Have you ever wondered the differences between the Trivalent and Quadrivalent vaccine? They are actually corresponding to 3 and 4 different types of flu viruses. But actually how many flu viruses are existing right now? Which one is the most contagious? What is the virus currently spreading around the world? Let’s learn more about different types of flu viruses below.

How different are the 4 types of flu viruses?

There are 4 types of flu viruses: A, B, C and D, all can infect people except for type D. Through constant mutations, flu A&B can form new subtypes leading to another outbreak of seasonal flu. The main differences of the viruses are listed below:

FLU A

More contagious and easier to cause illness, the major virus that causes seasonal flu
Common symptoms include: fever, chills, headache, cough, sore throat and runny nose
More severe illness and higher death rate in general
New wave of flu outbreak can arise from a new subtype of type A virus

Flu B

Similar symptoms with type A virus
Less severe illness and lower death rate than type A virus
Generally change more slowly in terms of genetic and antigenic properties than flu A

Flu C

Less severe symptoms than flu A&B such as runny nose, sore throat and coughs
Rarer and less likely to cause pandemic

Flu D

Similar symptoms with type A virus
Less severe illness and lower death rate than type A virus
Generally change more slowly in terms of genetic and antigenic properties than flu A

As of today, many countries including the US and Australia have suggested that the majority of flu cases this year were due to flu A, which is known to cause more severe epidemics.

What are the subtypes of Flu A&B?

Flu A viruses are divided into subtypes based on 2 proteins on the surfaces of the virus: hemagglutinin (H) and neuraminidase (N). There are 18 different H subtypes and 11 different N subtypes (H1-H18 and N1-N11), constituting to more than 130 flu A subtype combinations discovered now in nature. Most common seasonal flus in Hong Kong now are H1N1 and H3N2.

Flu B viruses can be further classified into 2 lineages: B/Yamagata and B/Victoria.