Final answer:
Correct option (B), "some sources say the flu vaccine could lessen negative effects on the economy." The article 'What a Bad Flu Season Could Cost the US Economy' emphasizes that the flu vaccine could potentially lessen the negative economic impacts of a bad flu season.
Step-by-step explanation:
To determine which idea is explicitly stated in the article "What a Bad Flu Season Could Cost the US Economy," we can look at the information provided. Based on the references, the correct answer seems to be option B - some sources say the flu vaccine could lessen negative effects on the economy. This is because the article discusses the benefits of flu vaccines in terms of economic as well as health outcomes, namely the prevention of a bad flu season which can be costly to the economy. The vaccination programs are seen in a positive light in terms of preventing the flu and mitigating its impact on society and the economy at large.