In April 2009, a flu subtype spreading from Mexico caused global fear. What was it called?

Explanation

Swine influenza is an infection by any one of several types of swine influenza viruses. Swine influenza is of influenza type A, and there are four known virus subtypes - H1N1, H1N2, H2N1, H3N1, H3N2. It can be transmitted to humans, but until recently, this had only happened for people with regular exposure to pigs. In April 2009, however, something new happened as, for the first time, a swine influenza virus was transmitted directly from humans to humans. A pandemic was declared by WHO on 11 June 2009.