The WHO and the CDC reacted strongly to the 2009 outbreak of H1N1 influenza, a.k.a. swine flu. But you don't need to panic just yet.
The new strain of H1N1 flu ("swine flu") that emerged in Mexico in April 2009 has caused a major response from the U.S. Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO). By the end of April, the WHO had raised its pandemic alert level to phase 5, indicating "widespread human infection" [1]. Meanwhile, the CDC "continues to take aggressive action to respond to an expanding outbreak" [2]. What does all of this mean?
The CDC H1N1 Flu Response
The CDC's mission is to play the central role in preventing and controlling diseases in the United States. In its official mission statement, it claims to be "responsible for controlling the introduction and spread of infectious diseases" [3]. In the case of a potentially serious pandemic such as H1N1 flu, the CDC does not play around. It acts quickly and aggressively to be able to mitigate the spread and impact of the disease, even in the worst case scenario. The CDC response is designed for the gravest possible situation with H1N1 flu: a very contagious, very virulent virus with a high death rate.
The CDC H1N1 response does not mean that we actually are in the worst case scenario. On the contrary, at the current time the situation is far less severe than our worst fears, with confirmed cases increasing fairly slowly [4].
The WHO H1N1 Flu Response
The WHO, a part of the United Nations, "is responsible for providing leadership on global health matters" [5]. Like the CDC, its H1N1 flu response is fast and aggressive in order to minimize the effects of a worldwide outbreak. The WHO's actions are designed to control the global pandemic in case the swine flu virus proves highly deadly and easily spread.
When the WHO raised its Epidemic and Pandemic Alert and Response (EPR) from Phase 4 to Phase 5 on April 29, the entire world took notice. Phase 5 indicates that there is "human-to-human spread of the virus into at least two countries in one WHO region" (in this case, Mexico and the United States) and that a "pandemic is imminent" [6]. While the WHO's language seems alarming, a very important point must be remembered: the EPR has to do only with the spread of a flu virus, not with its virulence (severity) or mortality. Phase 5 does not mean that the virus is likely to cause deaths, only that it is likely to spread.