Medical News Today: Influenza A vs. B: What to know

Influenza A and B differ in terms of how common they are.


According to researchers, influenza A viruses are responsible for about 75% of confirmed flu cases, while influenza B viruses are behind approximately 25% of confirmed cases.


Both influenza A and B are highly contagious.

When a person with the flu coughs or sneezes, droplets can enter another person’s nose or mouth, transmitting the illness.

According to the Centers for Disease Control and Prevention (CDC), flu viruses can infect others from up to 6 feet away.

Alternately, a person can catch the flu if they touch a surface contaminated with the flu virus, then touch their own mouth or nose.

The CDC report that people with the flu are the most contagious in the 3–4 days after becoming ill. Symptoms tend to develop 2 days after the illness starts, so a person may pass on the flu before they feel sick.


For a person who is generally healthy, the flu is not typically dangerous. However, it can severely affect certain groups of people, who should seek medical attention as soon as they suspect that they have flu symptoms.

Those most at risk of developing flu complications include:

  • women who are pregnant
  • people with certain chronic medical conditions
  • children younger than 5
  • adults aged 65 or over

Many people believe that influenza A is more severe than influenza B. However, this is not always the case.

A 2014 study concluded that adults hospitalized with influenza A or B tended to have similarly long hospital stays. They also had similar rates of intensive care unit admission and death during hospitalization.

A 2016 study found that the influenza B virus was more likely to cause death in hospitalized children aged 16 or younger.

The researchers also concluded that children aged 10–16 years with this type of virus were more likely to be admitted to intensive care units, compared with those who had influenza A.

Source Article from


メールアドレスが公開されることはありません。 * が付いている欄は必須項目です