Major Finding: Between April 2009 and Dec. 12, 2009, there were an estimated 55 million cases of H1N1 influenza in the United States; between 7,880 and 16,460 of those infected have died. By Jan. 2, 2010, 61 million Americans had been vaccinated, including 38% of individuals in the limited vaccine subset of the initial target groups.
Data Source: Centers for Disease Control and Prevention.
Disclosures: None reported.
Between 39 million and 80 million individuals in the United States contracted 2009 influenza H1N1 between April 2009 and Dec. 12, 2009, according to data collected by the Centers for Disease Control and Prevention.
The midlevel of the estimated range is 55 million individuals.
Of those infected with H1N1 influenza, an estimated 173,000-362,000 have been hospitalized, and between 7,880 and 16,460 have died, the CDC reported.
About 18 million children 0-17 years of age contracted the virus. Adults 18-64 years of age accounted for another 32 million cases, and there were 5 million cases among individuals 65 years of age and older.
According to the results of two surveys, an estimated 61 million persons (20% of the U.S. population) had received the monovalent H1N1 vaccine by Jan. 2, 2010, including 29% of children and 22% of health care personnel (MMWR 2010;59:1-5).
About 28% of the people in the initial target groups and 38% of those in the limited vaccine subset received at least one dose of the vaccine. The initial target groups included:
▸ pregnant women
▸ persons who live with or care for infants less than 6 months of age
▸ young adults aged 6 months to 24 years, and
▸ persons aged 25-64 years with certain medical conditions.
The limited vaccine subset included:
▸ pregnant women,
▸ persons who live with or care for infants less than 6 months of age,
▸ health care and emergency services personnel,
▸ children aged 6 months to 4 years, and
▸ children aged 5-18 years with certain medical conditions.
The data came from two telephone surveys: the National 2009 H1N1 Flu Survey (NHFS) and the Behavioral Risk Factor Surveillance System (BRFSS).
At an estimated 33%, the vaccination rate was highest among children 6 months to 4 years of age. The lowest rate, 11%, was found among adults 65 years of age and older.
“The results in this report show that nearly 90% of adults aged [less than] 65 years with medical conditions that increase their risk for influenza-related complications remain unvaccinated,” wrote J. A. Singleton and colleagues at the CDC. “Given the increased supply of vaccine, efforts to encourage 2009 H1N1 vaccination among persons at increased risk for … complications should be strengthened.”
Pregnant women have been hit hard by H1N1 flu, both in terms of hospitalization rates and mortality, as reported elsewhere.
The 38% H1N1 vaccination coverage among pregnant women in this report was higher than the typical rate of 15%-25% seen with seasonal flu vaccination, but the confidence interval of 24%-52% is large.
A separate data collection system, the Pregnancy Risk Assessment Monitoring System (PRAMS), involving approximately 30,000 women with live births in 31 states, will provide more precise estimates in the future, the investigators said.
The surveys also revealed lower vaccination coverage among blacks than whites, similar to the disparities seen in seasonal vaccine coverage.
“The finding of lower 2009 H1N1 coverage among black heath care workers suggests that access to care is not the only barrier to influenza vaccination and highlights a role for targeted outreach efforts,” they wrote.