Measles is highly contagious; what is the approximate secondary attack rate after exposure?

Measles is highly contagious; what is the approximate secondary attack rate after exposure?

• A. 50%
• B. 90%
• C. 10%
• D. 30%

Answer: (B)

Measles spreads very easily from an infectious person to those who are susceptible, so the chance that exposed, nonimmune contacts become infected is extremely high. The secondary attack rate in this situation is around 90%, meaning about 9 of 10 susceptible contacts exposed to an infectious individual will contract measles. This reflects the virus’s high transmissibility and its capacity to spread through both droplets and airborne routes, even before the rash appears. Vaccination reduces susceptibility, so in vaccinated or previously infected individuals the secondary attack rate drops dramatically. The other options are too low to reflect the power of measles transmission in a susceptible group.

Measles spreads very easily from an infectious person to those who are susceptible, so the chance that exposed, nonimmune contacts become infected is extremely high. The secondary attack rate in this situation is around 90%, meaning about 9 of 10 susceptible contacts exposed to an infectious individual will contract measles. This reflects the virus’s high transmissibility and its capacity to spread through both droplets and airborne routes, even before the rash appears. Vaccination reduces susceptibility, so in vaccinated or previously infected individuals the secondary attack rate drops dramatically. The other options are too low to reflect the power of measles transmission in a susceptible group.