18748
Using a mean IC50 cut - off of 50 , sera from control rabbits immunized with gp120 alone neutralized only one virus of the 14 non - Tier 1 viruses tested ( 7 % ) , whereas sera from b121a - and b122a - immunized rabbits neutralized seven ( 50 % ) and twelve ( 86 % ) viruses , respectively .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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