This is the 1991st most frequent Japanese word.
インフルエンザ
The Japanese word "インフルエンザ" means "influenza" or "the flu" in English.
The word "インフルエンザ" in this sentence refers to the flu as a disease, emphasizing the health action taken to prevent it.
インフルエンザにかかることを避けるために、予防接種を受けました。
I got vaccinated to avoid catching the flu.
Here "インフルエンザ" is used to describe the flu outbreak of the year and its severity.
今年のインフルエンザは症状が重いので、注意が必要です。
This year's flu has severe symptoms, so precautions are necessary.
In this case, "インフルエンザ" refers generically to the flu as a seasonal illness that commonly occurs.