Which of the following is an infectious disease caused by a virus for which there is no vaccine?

• A. Flu
• B. Measles
• C. Cold
• D. Chickenpox

Answer: (C)

The concept here is that vaccines exist for some viral infections but not for all. The common cold is caused by many different viruses—primarily rhinoviruses, but also coronaviruses and others. Because there are so many distinct viruses and they vary a lot, creating a single vaccine that protects against all of them isn’t feasible. That’s why there’s no vaccine for the common cold.

In contrast, diseases like influenza, measles, and chickenpox are each caused by more specific viruses for which vaccines have been developed and implemented. Influenza vaccines target circulating flu strains each season, measles has an effective measles vaccine as part of the MMR vaccination, and chickenpox has a vaccine against varicella-zoster virus.