Final answer:
New flu vaccines are needed each season because the influenza virus mutates rapidly, requiring updated vaccines to protect against current strains. so, option A is the correct answer.
Step-by-step explanation:
The reason new flu vaccinations are required each new flu season is that the influenza virus undergoes frequent genetic mutations. These mutations, especially in the virus's surface molecules, allow the virus to evade the immunity developed against previous strains. In contrast, viruses such as those causing measles, mumps, and rubella mutate very little, which means the same vaccine can be effective for many years. The rapid mutation rate of the influenza virus means that scientists and pharmaceutical companies must predict the most prevalent strains each year and develop vaccines accordingly to keep up with the ever-changing nature of the virus.
The reason new flu vaccinations are required for each new flu season is because the influenza virus undergoes frequent genetic mutations. These mutations occur in the surface molecules of the virus, allowing it to evade the protective immunity developed from previous vaccinations. As a result, individuals need to be vaccinated annually to ensure protection against the most current flu strains.