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Questions & Answers

2009 H1N1 Flu In The News

May 14, 2010 2:30 PM ET

How many 2009 H1N1 cases, hospitalizations and deaths are estimated to have occurred in the United States?

On May 14, 2010, CDC issued updated estimates of the number of 2009 H1N1 cases, hospitalizations and deaths for the United States from April 2009 through April 10, 2010.

• CDC estimates that between 43 million and 89 million cases of 2009 H1N1 occurred between April 2009 and April 10, 2010. The mid-level in this range is about 61 million people infected with 2009 H1N1.
• CDC estimates that between about 195,000 and 403,000 H1N1-related hospitalizations occurred between April 2009 and April 10, 2010. The mid-level in this range is about 274,000 2009 H1N1-related hospitalizations.
• CDC estimates that between about 8,870 and 18,300 2009 H1N1-related deaths occurred between April 2009 and April 10, 2010. The mid-level in this range is about 12,470 2009 H1N1-related deaths.

This method uses surveillance data on 2009 H1N1 hospitalizations collected through CDC’s Emerging Infections Program (EIP), which conducts surveillance for laboratory-confirmed influenza-related hospitalizations in children and adults. CDC has issued updated estimates using the same methodology about every 4 weeks since the first estimates were issued on November 12, 2009. The first estimates were for the number of 2009 H1N1 cases, hospitalizations and deaths for April through October 17, 2009. Updated estimates for April through November 14, 2009 were issued on December 10, 2009; updated estimates for April through December 12, 2009 were issued on January 15, 2010; updated estimates for April through January 16, 2010 were issued on February 12, 2010; updated estimates for April through February 13, 2010 were issued on March 29, 2010; and updated estimates for April through March 13, 2010 were issued on April 19, 2010. The same methodology was applied to derive each set of estimates.

The latest estimates incorporate an additional four weeks of flu data (from March 14, 2010 through April 10, 2010) from the previous estimates released on April 19, 2010. The latest estimates show a relatively small increase in the total number of 2009 H1N1 cases, hospitalizations and deaths since the previous estimates posted on April 19, 2010.
A table showing this data by age group is available. In addition, background information on these estimates and information about the methodology used to generate these estimates also is available.

Although sporadic cases of influenza are expected to occur during the summer months, no additional updated estimates using this method are planned since influenza activity is now at a low level in the United States and few flu-related hospitalizations and deaths are expected over the summer.

Who has been most impacted by 2009 H1N1, according to CDC’s estimates?

CDC’s latest estimates of 2009 H1N1-associated cases, hospitalizations and deaths continue to confirm the fact that people younger than 65 years of age have been more severely affected by this disease relative to people 65 and older. This is in stark contrast to seasonal flu, where about 60 percent of seasonal flu-related hospitalizations and 90 percent of flu-related deaths occur in people 65 years and older. With 2009 H1N1, about 90% of estimated hospitalizations and 87% of estimated deaths from April 2009 through April 10, 2010, occurred in people younger than 65 years old. Like seasonal flu, however, people with certain underlying health conditions were at a greater risk of serious hospitalization and death from this virus. Of hospitalized adults and children with 2009 H1N1, 80% of adults and about 60% of children had underlying health conditions previously associated with conferring a greater number of flu complications. 

What is CDC recommending at this time?

CDC recommends influenza vaccination as the first and most important step in protecting against the flu. Flu is unpredictable, but sporadic cases of 2009 H1N1 continue to be detected in the United States and 2009 H1N1 viruses are being reported in other parts of the world. Also, it’s possible that the United States could experience early 2009 H1N1 flu activity next season, before seasonal flu vaccine is available.  Therefore, CDC continues to encourage 2009 H1N1 vaccination for anyone who wants to protect themselves against 2009 H1N1. This might be especially applicable to people who are traveling to areas where 2009 H1N1 is occurring, or people who are at higher risk of flu-related complications, but who have not yet received a 2009 H1N1 vaccine.  This includes young children and people 65 years and older. In addition, certain health conditions increase the risk of being hospitalized from 2009 H1N1, including lung disease, like asthma or chronic obstructive pulmonary disease (COPD), diabetes, heart, or neurologic disease, and pregnancy. In addition, minority populations have been harder hit by the 2009 H1N1 pandemic than non-minority groups (See “Information on 2009 H1N1 impact by Race and Ethnicity.)”There also is growing evidence to support early concerns that people who are morbidly obese are at greater risk of serious 2009 H1N1 complications.