pandemic influenza




On April 29, 2009, in response to the global spread of a new “H1N1” strain of influenza, the World Health Organization (WHO) raised its influenza (“flu”) pandemic alert level to Phase 5, one level below declaring that a global influenza pandemic was underway. On June 11, as the virus continued to spread on several continents, WHO declared the outbreak to be an influenza pandemic (Phase 6). WHO’s pandemic declaration is based on the geographic spread of the virus, not on a worsening of the severity of illnesses it causes.

Officials now believe the outbreak of the new flu strain began in Mexico in March 2009, or perhaps earlier. The novel “H1N1 swine flu” was first identified in California in late April. Health officials quickly linked the new virus to many of the illnesses in Mexico. Since then, cases have been reported around the world. As of June 11, 2009, almost 29,000 cases were reported in 74 countries, on all continents but Antarctica. Most of the reported cases are in Mexico, the United States, and Canada. However, increasing numbers of cases are now reported in Argentina, Chile, Australia, and other countries in the Southern Hemisphere, as their winter approaches and flu transmission becomes more efficient. Health officials note that reported cases likely represent only a fraction of actual infections. For example, a U.S. official commented in May that there may actually have been upwards of 100,000 cases thus far in the United States.

2009 Influenza Pandemic Status

International: World Health Organization (WHO): Outbreak Status as of June 11, 2009 (

• WHO declared an influenza pandemic (Phase 6) on June 11, 2009.
• WHO reports almost 29,000 cases in 74 countries around the world, including 144 deaths. Most of the reported deaths occurred in Mexico.
• WHO advises no restriction of regular travel or closure of borders; however, sick individuals are advised to delay travel. No infection risk from consumption of well-cooked pork products.

United States Centers for Disease Control and Prevention (CDC), Food and Drug Administration (FDA): Outbreak Status as of June 5, 2009

• CDC reports a total of 13,217 cases in all 50 states, DC, and PR, including 27 deaths. Officials say that reported cases most likely underestimate the actual number of infections.
• The Acting Health and Human Services Secretary declared a public health emergency on April 26.
• CDC has released to states 11 million treatment courses of the antiviral drugs Tamiflu and Relenza, and sent an additional 400,000 courses to Mexico.
• FDA has issued Emergency Use Authorizations for certain unapproved uses of Tamiflu and Relenza, and for use of an unapproved diagnostic test for the new H1N1 strain.
• CDC has issued mitigation guidance for the general public; specific guidance for clinicians and laboratories, and regarding pregnant women and other groups; and recommendations for affected schools and communities. CDC rescinded a prior recommendation against non-essential travel to Mexico.
• Federal government and manufacturers are developing a vaccine against the new H1N1 strain.

The new flu strain responsible for the outbreak is an apparent reassortment of several existing strains of influenza A subtype H1N1 virus, including strains typically found in pigs, birds, and humans (see box below). The U.S. Centers for Disease Control and Prevention (CDC) reports that the symptoms and transmission of the novel H1N1 flu from person to person are much like that of seasonal flu. Laboratory testing of the new strain indicates that the antiviral drugs oseltamivir (Tamiflu) and zanamivir (Relenza) are expected, in most cases, to be effective in treating illnesses that result from this new strain.

In response to the situation, Janet Napolitano, Secretary of the Department of Homeland Security (DHS), has assumed the role of Principal Federal Official, coordinating federal response efforts. Charles E. Johnson, then the Acting Secretary of Health and Human Services (HHS), declared a public health emergency. Among other things, this allowed the Food and Drug Administration (FDA) to issue Emergency Use Authorizations (EUAs), permitting certain unapproved uses of Tamiflu and Relenza (such as in very young children), as well as the use of an unapproved diagnostic test for the new flu strain, and unapproved uses of some types of protective facemasks.

CDC has released stocks of Tamiflu and Relenza, respiratory protection devices, and other medical supplies, from the Strategic National Stockpile (SNS), to help states respond to the outbreak. CDC reports that it has released to state health officials 11 million of the 50 million treatment courses of Tamiflu and Relenza stockpiled in the SNS, and purchased additional courses to replenish the stockpile. CDC also has activated its Emergency Operations Centers to coordinate the agency’s response to the outbreak, and sent 400,000 treatment courses of antiviral drugs to Mexico. CDC’s initial advice to travelers to postpone all non-essential travel to Mexico has been rescinded, and travelers are now urged to take appropriate precautions while traveling.

According to DHS, U.S. border control agents are visually inspecting incoming travelers from Mexico, and referring those who appear to be sick to CDC quarantine stations or local health officials. Administration officials have resisted calls to implement more aggressive measures such as closing the U.S.-Mexico border, noting that the new flu strain is already in the United States and that the focus of mitigation strategies is on where U.S. illnesses are being reported, and on patients’ families and their surrounding communities.

In the United States, many affected communities implemented school closures when students were found to be infected with the new H1N1 flu strain. Those decisions, made by local officials, were based on an initial CDC recommendation that communities with confirmed H1N1 flu cases consider closing schools for up to 14 days, depending on the extent and severity of illness. CDC revised its initial guidance as it became clear that the virus was circulating widely in affected communities and that illnesses caused by the new strain were generally mild. It now recommends against routine school closures when small number of students are infected, arguing that such closures do little to reduce the spread of a virus that is already in circulation while placing a considerable burden on the affected community. CDC’s actions and those of local education authorities illustrate the challenges facing government officials as they attempt to make evidencebased decisions about community mitigation interventions in a constantly changing environment.

Health officials note that as the new flu strain spreads and the number of reported cases grows, precise case counts are less meaningful for purposes of disease control. The CDC has begun tracking illnesses at the population (rather than individual) level using its multi-layered surveillance system for seasonal flu, which tracks hospitalizations, outpatient medical visits, and other measures. One CDC official commented that reported cases of H1N1 flu probably represent only a fraction of actual cases, saying that early findings from the seasonal flu surveillance systems suggest that the actual number of cases in the United States thus far may be upwards of 100,000.

The U.S. response to the current situation triggers a slate of pandemic flu plans that were developed, beginning around 2004, to address concerns about the global spread of another novel flu strain, the H5N1 avian flu. In FY2006 supplemental appropriations, Congress provided $6.1 billion for pandemic planning across several departments and agencies.2 These earlier efforts, and others aimed at preparedness for bioterrorism and emerging infections in general, have generally streamlined the response to the new H1N1 flu.

Source :
The 2009 Influenza Pandemic: An Overview
Sarah A. Lister Specialist in Public Health and Epidemiology
C. Stephen Redhead Specialist in Health Policy
June 12, 2009

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