104. The major reason for the preparation of different influenza vaccines each year is that
Answer: D
The major reason for the preparation of different influenza vaccines each year is that the many viruses that cause flulike symptoms in humans vary from year to year.
Each year, different strains of the influenza virus circulate among the population, necessitating the preparation of new vaccines to provide effective immunity. This variability in viruses is a significant factor in the annual vaccine formulation.
A) viruses do not live long enough to permit a vaccine to be used more than one year
This option is incorrect because while influenza viruses can mutate, the primary reason for changing vaccines annually is not related to their lifespan. Vaccines are developed based on the specific strains that are prevalent each year, rather than the longevity of the viruses themselves.
B) antibodies to viruses undergo modifications in the bloodstream
This option is also incorrect. Antibodies do evolve over time in response to infections, but the need for new vaccines is primarily due to changes in the circulating virus strains rather than modifications of antibodies in the bloodstream.
C) many more animal viruses are cross-infecting humans now than before
This statement is misleading and not the primary reason for yearly vaccine updates. While cross-species transmission can occur, the necessity for yearly vaccine reformulation is predominantly driven by the antigenic variation of the influenza viruses that circulate among humans.
D) the many viruses that cause flulike symptoms in humans vary from year to year
This option is correct. The influenza virus has a high mutation rate, leading to the emergence of new strains each year. Therefore, vaccines must be updated annually to match the specific strains that are expected to be in circulation, ensuring effective immunity in the population.
Conclusion
The correct answer, option D, accurately reflects the need for annual vaccine updates due to the variation of influenza viruses from year to year. Other options fail to address the core issue of viral variability and the specific strains that cause seasonal outbreaks, which is fundamental to influenza vaccine development.