Simplify the following text for a Grade 5 native English-speaking person.
Original: As of 2009 , the known SIV strains include influenza C and the subtypes of influenza A known as H1N1 , H1N2 , H3N1 , H3N2 , and H2N3 .
Simplified: Types of flu strain include H1N1 , H1N2 , H3N1 , H3N2 , and H2N3 . are known to cause swine influenza .