2009 H1N1 Pandemic Timeline

In 2009, a new H1N1 influenza virus emerged, causing the first global flu pandemic in 40 years. Below is a timeline of major events that took place during the 2009 H1N1 pandemic.

  • Timelineicon
    image of h1n1 virus
    April 15
    • First human infection with new influenza A H1N1 virus detected in California.
  • Timelineicon
    April 17
    • Second human infection with the new influenza A H1N1 virus detected in California about 130 miles away from first infection, with no known connection to previous patient.
  • Timelineicon
    April 18
    • First novel 2009 H1N1 flu infections were reported by CDC to the World Health Organization (WHO) through the U.S. International Health Regulations Program.
  • Timelineicon
    April 21
    • CDC publicly reported the first two U.S. infections with the new H1N1 virus.
    • CDC began working to develop a candidate vaccine virus.
  • Timelineicon
    room with people on computers
    April 22
    • CDC activated it’s Emergency Operations Center (EOC).
  • Timelineicon
    April 23
    • Two additional human infections with 2009 H1N1 were detected in Texas, transforming the investigation into a multistate outbreak and response.
  • Timelineicon
    person in lab using equipment
    April 24
    • CDC uploaded complete gene sequences of new H1N1 2009 virus to a publically-accessible international influenza database.
  • Timelineicon
    April 25
    • The World Health Organization (WHO) declared a public health emergency of international concern.
  • Timelineicon
    person watching television
    April 26
    • The United States Government declared 2009 H1N1 a Public Health Emergency of International Concern and CDC began releasing 25% of antiviral drugs needed to treat this new influenza virus from the federal stockpile.
  • Timelineicon
    April 27
    • WHO Director-General raised the level of influenza pandemic alert from phase 3 to phase 4, based on data showing person-to-person spread and the ability of the virus to cause community-level outbreaks.
  • Timelineicon
    April 28
    • The Food and Drug Administration (FDA) approves new CDC test to detect 2009 H1N1 infections
  • Timelineicon
    April 29
    • WHO raised the level of influenza pandemic alert from phase 4 to phase 5, signaling that a pandemic was imminent, and requested all countries immediately activate their pandemic preparedness plans and be on high alert for unusual outbreaks of influenza-like illness and severe pneumonia.