In a village of 100 children, 60% are immunized against measles. One child travelled outside and returned with measles and infected other 26 children. What is the secondary attack rate

Ans. is 'a', i.e 67% Secondary attack rate : No. of exposed persons developing the disease within the range of incubation period following exposure to the primary case. SAR = (No. of exposed persons developing the disease within the range of incubation period) x 100 / (Total no. of exposed/susceptible contacts)Total no. of children = 100Total no. of immunize = 60No. of susceptible = 39Since out of 40 unimmunized children one has already contacted the disease.No. of exposed persons developing the disease = 26So SAR= (26 / 39 ) x 100 =200/3 = 67%