This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
Von magnus phenomenon is 
Select and explain. 
A. High hemagglutinin titre, low infectivity, B. High hemagglutinin titre, high infectivity, C. Low hemagglutinin titre, low infectivity, D. Low hemagglutinin titre, High infectivity
A: High hemagglutinin titre, low infectivity
Answer: A: High hemagglutinin titre, low infectivity 
Explanation: Commonly hemagglutinin titre α Infectivity but in Von-Magnus phenomenon - High hemagglutinin titre, Low infectivity due to mutation in virulent gone.