In polio transmission, wild-type PV may spread more readily in populations with what condition?

• A. Climate change
• B. Economic growth
• C. No sanitation
• D. Unimmunized or under-immunized populations

Answer: (D)

Polio spreads mainly through the fecal-oral route, so how easily it moves through a community depends on how many people are susceptible to infection. When a large portion of the population hasn’t been vaccinated or hasn’t developed immunity, there are many susceptible hosts. The virus can pass from person to person more freely, leading to more infections and a higher risk of paralysis among those who are susceptible. Vaccination reduces the number of people who can be infected and, through herd immunity, can interrupt transmission even if the virus is introduced.

Climate change or economic growth don’t directly determine how easily the virus spreads. Poor sanitation can help transmission, but the strongest predictor of rapid spread is the level of immunity in the population; unimmunized or under-immunized communities are most at risk because they provide abundant susceptible hosts for the virus to move through.