Questions & Answers

2009 H1N1 Flu In The News

March 12, 2010 4:00 PM ET

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

On March 12, 2010, CDC issued updated estimates of the number of 2009 H1N1 cases, hospitalizations and deaths for the United States from April 2009 through February 13, 2010.

• CDC estimates that between 42 million and 86 million cases of 2009 H1N1 occurred between April 2009 and February 13, 2010. The mid-level in this range is about 59 million people infected with 2009 H1N1.
• CDC estimates that between about 188,000 and 389,000 H1N1-related hospitalizations occurred between April 2009 and February 13, 2010. The mid-level in this range is about 265,000 2009 H1N1-related hospitalizations.
• CDC estimates that between about 8,520 and 17,620 2009 H1N1-related deaths occurred between April 2009 and February 13, 2010. The mid-level in this range is about 12,000 2009 H1N1-related deaths.

CDC first provided estimates for the number of 2009 H1N1 cases, hospitalizations and deaths for April through October 17, 2009 on November 12, 2009 and committed to updating those estimates approximately monthly. 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; and updated estimates for April through January 16, 2010 were issued on February 12, 2010. The same methodology was applied to derive each set of estimates.

The latest estimates incorporate an additional four weeks of flu data (from January 17, 2010 through February 13, 2010) from the previous estimates released on February 12, 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 February 12, 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.

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 highlight the fact that people younger than 65 years of age are more severely affected by this disease relative to people 65 and older compared with seasonal flu. 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 February 13, 2010, occurred in people younger than 65 years old. Although there have been severe infections and deaths from 2009 H1N1 in every age group, including people 65 and older, the largest burden has fallen on people younger than 65.

What is CDC recommending at this time?

CDC is continuing to recommend vaccination against 2009 H1N1 at this time for all people 6 months and older, including those people 65 years of age and older because severe illness and deaths have occurred in this age group.  Ongoing vaccination of people with certain health conditions is particularly important because most cases of serious 2009 H1N1 illness (e.g., hospitalizations) have occurred in people with underlying medical conditions. (See “2009 H1N1 Flu: Underlying Health Conditions among Hospitalized Adults and Children.”) Health conditions that increase the risk of being hospitalized from 2009 H1N1 include lung disease like asthma or chronic 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.

What does this data indicate with regards to 2009 H1N1 vaccination recommendations?

This data supports the recommendations made in July by the Advisory Committee on Immunization Practices (ACIP) that initial doses of 2009 H1N1 vaccine be prioritized for people who were more likely to get infected and become very ill. This included all children and young adults 6 months through 24 years old, pregnant women, and adults 25 through 64 years of age with a health condition associated with higher risk of medical complications from flu. People 65 and older were not prioritized for vaccination initially because they were less likely to become sick relative to people in other age groups. It was recognized however, that people age 65 and older were at high risk for serious complications if they were to become ill, and for that reason, people in that age group were prioritized to get antiviral drugs if they became sick. The rationale for how the initial target groups for vaccination were identified is described in the transcript   (1MB) and slide presentations from the July ACIP meeting. The rationale behind this decision was again covered in an ACIP meeting in October 2009 and the slides from this meeting are publicly available as well. The full ACIP recommendations on the use of 2009 H1N1 vaccine  are available online. Although people 65 and older were not included in the initial groups recommended to get the earliest doses of vaccine, as soon as supplies of the vaccines to protect against the 2009 H1N1 virus were sufficiently large, CDC encouraged programs to opened up vaccination to anyone who wanted it, including people 65 and older. A special day (Friday, January 15, 2010) during National Influenza Vaccination Week (NIVW) was designated to raise awareness about the importance of vaccination in people 65 years and older. CDC continues to recommend that anyone 6 months or older who wants to be protected from the 2009 H1N1 virus be vaccinated, regardless of age.

• Page last reviewed: March 12, 2010 1:00 PM ET
• Page last updated: March 12, 2010 1:00 PM ET
• Content source: Centers for Disease Control and Prevention