The influenza vaccine is updated annually because the virus mutates. Choose the correct option.

• A. NOT ENOUGH INFO
• B. FALSE
• C. ONLY SOME YEARS
• D. TRUE

Answer: (D)

The main idea is that influenza evolves over time, changing the virus’s surface proteins that vaccines target. Because those proteins can drift from year to year (and sometimes shift more drastically), scientists update the vaccine composition annually to match the strains expected to circulate in the upcoming season. This yearly reformulation helps keep protection as high as possible, even though effectiveness can vary by year. So the statement is true. The other options don’t fit: mutation is well documented, so “NOT ENOUGH INFO” isn’t correct; the claim isn’t false; and the vaccine is updated every year, not only some years.