Which two strains of virus are mentioned in the context of mortality rates?

The mention of variola major and variola minor in the context of mortality rates is significant due to their association with smallpox, a highly contagious and deadly disease caused by the variola virus. Variola major is the more severe form, with historically high mortality rates—often exceeding 30%—while variola minor generally has a much lower mortality rate. This distinction is critical in understanding infectious diseases and their potential impact on public health.

In contrast, the other options address viral strains that are also significant in terms of their effects on human health, but they pertain to different diseases or contexts. For example, Ebola and Marburg are well-known for high mortality rates, but the question specifically inquired about the strains historically categorized under smallpox. Similarly, although Influenza A and B are important in terms of morbidity and mortality, the mortality rates associated with them are generally lower compared to variola major. HIV and Hepatitis C also have serious implications for health but are chronic conditions rather than acute viral illnesses with defined mortality rates like those of smallpox. Thus, the historical and clinical relevance of variola major and minor specifically links them to discussions about mortality rates in a more direct manner.