Final answer:
The timeframe for vaccinating a population against influenza cannot be determined without specific context, but it is important to vaccinate annually due to influenza's rapid mutation through antigenic drift and shift.
Step-by-step explanation:
The question regarding how quickly a population can be vaccinated against a virulent strain of influenza depends on several factors, including the speed of vaccine production, the effectiveness of vaccination programs, and the accessibility of the vaccine to the population. Influenza is a highly contagious respiratory illness that can cause severe acute illness and lead to pandemics. The correct answer to how quickly this can be done is not provided in the question, as it varies based on specific health infrastructure and logistics. However, new influenza vaccines are developed annually due to the virus's ability to mutate rapidly through antigenic drift and antigenic shift, which is the main reason individuals need to be vaccinated each year.
Each year's influenza vaccine is formulated based on a recommendation of the predominant strains. These vaccines are important because, without immunization, the flu can spread quickly and lead to hospitalizations and deaths. Antigenic drift and shift result in new strains that can evade the previous year's immune protection. Hence, annual vaccination is crucial for effective influenza control, especially considering the potential for new pandemics arising from strains like H5N1 or the H7N9 virus, which have shown high mortality rates in past outbreaks.