The earliest smallpox vaccines were infected tissue rubbed into the skin of a healthy
person. The recipient of such a vaccine usually developed a mild case of smallpox, recovered, and was immune thereafter. What is the most likely reason this vaccine did not kill more people?
a. Skin is the wrong portal of entry for smallpox.
b. The vaccine consisted of a mild form of the virus.
c. Smallpox is normally transmitted by skin-to-skin contact.
d. Smallpox is a virus.
e. The virus mutated.

Verified step by step guidance

1. Understand the historical context of smallpox vaccination, which involved variolation, a method where material from smallpox sores was introduced into the skin.
2. Consider the nature of the smallpox virus and how it typically infects individuals.
3. Evaluate the options given: a) Skin is the wrong portal of entry for smallpox, b) The vaccine consisted of a mild form of the virus, c) Smallpox is normally transmitted by skin-to-skin contact, d) Smallpox is a virus, e) The virus mutated.
4. Analyze why the method of introducing the virus through the skin might have resulted in a milder infection, leading to immunity without severe disease.
5. Conclude that the most likely reason the vaccine did not kill more people is related to the nature of the virus and the method of administration, focusing on the option that best explains the mildness of the infection.

Key Concepts

Vaccination and Immune Response

Vaccination involves introducing a harmless form of a pathogen to stimulate the immune system. In the case of smallpox, the early vaccines used a mild form of the virus, which allowed the body to develop immunity without causing severe disease. This process helps the immune system recognize and combat the actual virus if encountered in the future.

Pathogen Characteristics

Understanding the characteristics of the smallpox virus is crucial. Smallpox is caused by the variola virus, which is highly infectious but can be effectively managed through vaccination. The mild form used in early vaccines did not cause severe illness, allowing for a safer immunization process.

Transmission Routes

The transmission of smallpox typically occurs through direct contact with infected individuals or contaminated objects. The fact that the vaccine was administered through the skin, rather than through respiratory routes, likely reduced the risk of widespread infection, as the virus was introduced in a controlled manner.