840
The geometric mean hemagglutination - inhibition antibody titers ( GMT ) of non - immunized , once - immunized , and twice - immunized chickens were compared at 2 - week intervals following primary immunization , secondary immunization , and challenge .
 None
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: GENE 
Text: {0} 
Answer:
 None