This year’s flu season appears to be among the worst in recent memory. Reports from the Centers for Disease Control and Prevention say the flu is currently spreading to large swaths of people in 46 states and has killed at least 106 people throughout the US. Several of these states are therefore dealing with significantly more flu-related hospitalizations than usual, particularly for people over 50 and very young children.

So between this flu season’s cost (possibly around $12 billion), timing (surprisingly early for the west coast) and range (literally every part of the continental US), you can expect it to set quite a few historic records. The scientific community isn’t entirely sure what is making this flu season so catastrophic but two factors are undeniably playing major roles, and the second factor is a direct result of the first.

Here’s why this flu season is affecting more people than previous years:

Not Your Average Strain

Each flu season involves different strains of the influenza virus. This year, the most widespread strain is "influenza A sub-type H3N2," which is said to be one of the most dangerous strains. Previous years in which H3N2 was the most widespread strain saw more hospitalizations and total infections than average. The unusually severe flu seasons from early 2013 and 2015, for example, were attributed to H3N2.

This year’s increase in cases is also likely due to the fact that this isn’t the only loathsome strain wreaking havoc on the US. Another strain called H1N1 has emerged in certain patches of the country as well. If that name sounds familiar, you’re right, but it used to go by a different name: swine flu. This virus was responsible for 274,304 hospitalizations in a year’s time and is estimated to have sickened 25% of the global population.

Vaccine Makers Were Caught Off Guard

According to Time, the flu vaccine is modified each year based on what is projected to be the most active strain. Sometimes, however, the projections aren’t exactly on point because it’s almost impossible to predict which strains are waiting to strike.

It seems that whatever modifications were made to the original vaccine are not as effective for H3N2, which is apparently the result of an unexpected mutation that caught researchers off guard. Studies have shown that the vaccine was only 10% effective in Australia but closer to 40% in the US. Vaccines for the average flu season in the US are reportedly 40% to 60% effective. This year’s vaccine is expected to be effective against 30% of H3N2 cases worldwide.

Should I Bother Getting The Shot?

The CDC still recommends getting vaccinated because even though the current vaccine might not completely eliminate the virus, it will most likely diminish symptoms. Previous research has found that the flu vaccine reduces the risk of infection by 40% to 60%. There is also up to 13 weeks of flu season left, and influenza B strains are known to emerge in the closing weeks. The vaccine could be more effective for this strain than H3N2.

What Else Can I Do To Avoid The Flu?

Aside from getting vaccinated, the most effective ways to decrease your risk of infection are washing your hands, cleaning surfaces that might contain flu germs, and staying home if you are sick. It’s easy to mistake a common cold for the flu but unless your congestion is accompanied with a fever, weakness and body aches, there’s no reason to worry. Actually, you shouldn’t even panic over contracting the flu itself because for most cases, the only things you can do to treat it are rest and stay hydrated. Only patients who have severe symptoms like trouble breathing are recommended to seek treatment.