Flu Vaccine is Only 10% Effective Against H3N2 this Season

Source: Vox. Justin Sullivan/Getty Images

Did you get the flu shot this year, but end up coming down with the flu anyways? Or do you notice a lot of people around you still sick? There is a reason for that!

The effectiveness of the flu shot is extremely low this year, preventing only 10% of H3N2 flu cases among the ages of 20 to 64 years old. This means that if 100 out of 1000 unvaccinated people develop the flu, the number of cases will only drop to 90 out of 1000 vaccinated people. Therefore, people who were vaccinated should not consider themselves invincible this season.

Typically, the effectiveness of the flu shot is between 50 and 70 percent. However, when the dominant H3N2 strain is circulating during a given year, the vaccine is less protective. This is the case for this year. Because the virus mutates rather quickly as it moves through a population, it makes it very hard to design a vaccine to fight against all of the different strains. Another reason why the vaccine against H3N2 is underperforming this year may have to do with eggs.

Source: Business insider

Vaccines are made through an egg-based production method. Flu viruses are injected into fertilized hen eggs and left to replicate for several days. The virus is then harvested from the egg and inactivated to go into vaccines. However, researchers have recently discovered problems with this approach, specifically related to H3N2. They have noticed that H3N2  mutates to adapt to the egg, which causes the vaccine to be less effective in humans.

Source: Fox News

Now you might be thinking, should you still get your flu shot? … YES! Even though the H3N2 virus is dominant this year, other types of influenza viruses are also circulating and the vaccine can help protect you against them. The vaccine is usually quite effective against H1N1, which is another subtype of influenza A, and strains of influenza B. You don’t know which one you’ll get !

The flu shot does not give you full immunity, therefore, you should always considered other protective measures along with it. For example, you should always wash your hands with warm water and soap, avoid close contact with higher-risk individuals such as the elderly and stay home when you are sick to minimize spreading it to others.

Even though the vaccine is not perfect, it is still the best protection we have against flu viruses!

– Tammy Tang