Which statement is correct regarding smallpox transmission?

The correct statement regarding smallpox transmission is that a person is infectious from rash onset until scabs separate. This means that the period during which an infected individual can spread the virus begins when visible symptoms—in this case, the characteristic rash—first appear. The infectious period continues until the scabs that develop from the rash have completely separated and healed. This aspect of the disease highlights the importance of monitoring symptoms and understanding the specific timeline of infectiousness for effective containment and prevention measures.

In other contexts, smallpox is not transmitted via contaminated water; it primarily spreads through respiratory droplets and direct contact with infected individuals or contaminated materials. Vaccination after exposure is not entirely ineffective, as it can provide some protection if administered within a specific timeframe following exposure, although it is most effective when given before exposure. While it is true that symptoms do not typically appear until about 7 to 17 days after exposure, this statement does not relate directly to the infectious period, which is critical for understanding transmission dynamics.