Nayer Khazeni, MD, MS; David W. Hutton, MS; Alan M. Garber, MD, PhD; Nathaniel Hupert, MD, MPH; Douglas K. Owens, MD, MS
Decisions on the timing and extent of vaccination against pandemic (H1N1) 2009 virus are complex.
To estimate the effectiveness and cost-effectiveness of pandemic influenza (H1N1) vaccination under different scenarios in October or November 2009.
Compartmental epidemic model in conjunction with a Markov model of disease progression.
Literature and expert opinion.
Residents of a major U.S. metropolitan city with a population of 8.3 million.
Vaccination in mid-October or mid-November 2009.
Infections and deaths averted, costs, quality-adjusted life-years (QALYs), and incremental cost-effectiveness.
Assuming each primary infection causes 1.5 secondary infections, vaccinating 40% of the population in October or November would be cost-saving. Vaccination in October would avert 2051 deaths, gain 69Â 679 QALYs, and save $469 million compared with no vaccination; vaccination in November would avert 1468 deaths, gain 49Â 422 QALYs, and save $302 million.
Vaccination is even more cost-saving if longer incubation periods, lower rates of infectiousness, or increased implementation of nonpharmaceutical interventions delay time to the peak of the pandemic. Vaccination saves fewer lives and is less cost-effective if the epidemic peaks earlier than mid-October.
The model assumed homogenous mixing of case-patients and contacts; heterogeneous mixing would result in faster initial spread, followed by slower spread. Additional costs and savings not included in the model would make vaccination more cost-saving.
Earlier vaccination against pandemic (H1N1) 2009 prevents more deaths and is more cost-saving. Complete population coverage is not necessary to reduce the viral reproductive rate sufficiently to help shorten the pandemic.
Agency for Healthcare Research and Quality and National Institute on Drug Abuse.
Influenza A (H1N1) vaccine is now being distributed for use in vaccination programs.
This decision model for vaccination suggests that vaccinating 40% of the population in October would save more lives and money than similar vaccination coverage in November.
The model makes several assumptions that may not bear out given the unpredictability of H1N1 infection this fall. However, users can test their own assumptions with a model provided by the authors.
Earlier vaccination is estimated to prevent more deaths and cost less than would later vaccination for influenza A (H1N1).
The effective viral reproductive rate decreases over time, secondary to the development of immunity in individuals in the population who recover from infection. The R0 is the number of secondary infections caused by each primary infection in the susceptible population.
At R0 (number of secondary infections caused by each primary infection in a susceptible population) of 1.2, fewer individuals would become infected, so less immunity would develop and more individuals would require vaccination to decrease widespread transmission. However, at R0 of 1.8, a significant number of infections would occur, increasing population immunity and decreasing the number of individuals who would require vaccination to decrease widespread transmission.
The percentage of the population requiring vaccination to reduce widespread transmission increases with decreases in vaccine efficacy. The R0 is the number of secondary infections caused by each primary infection in the susceptible population.
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January 14, 2010
H1N1 Deaths and Lightning Strikes
TO THE EDITOR: Last month's article by Khazeni et al. (1) concludes that H1N1 vaccination of 40% of the American population would "...avert 2051 deaths...and save $469 million dollars." They recommend that earlier vaccination would save more lives and lead to additional savings during an H1N1 pandemic. The specificity of the number of lives saved and dollars saved made me curious about the specificity of the H1N1 data used for these calculations. In this study, the H1N1 positive cases were "based on a New York City telephone survey of influenza-like illness...and ...CDC data on cases of influenza-like illness testing positive for pandemic H1N1(1)." I visited the CDC website to review their definition of positive H1N1 cases, and was surprised to find fewer laboratory confirmed cases of H1N1 deaths than I expected. While the laboratory confirmed cases of H1N1 related death were relatively low, the CDC FluView website reported an increased number of doctor visits for influenza-like illness (ILI) in 2009 as compared to 2008 (2). Are we comfortable using ICD-9 codes for "influenza-like illness" to define an H1N1 infection after a massive TV campaign depicting a deadly viral pandemic sweeping the country? I checked the CDC data from April-October 2009 which described only 95 laboratory confirmed H1N1 deaths in American children (3). They mentioned that fewer than half of these cases were tested for bacterial infection, and reported that Staphylococcus was identified in many of the cases that were tested (3). Did these children die from secondary Staphylococcal septocemia or H1N1 viral pneumonia? Lets assume that bacterial sepsis had nothing to do with these deaths, and 95 American children died from laboratory confirmed H1N1 between April and October. This data from the CDC confirms that approximately 15 of the 74 million American children (0.00002%) died from laboratory confirmed H1N1 infection per month nationwide and that 99.99998% did not. Is this a legitimate cause for level 6 pandemic precautions with universal vaccination costing over $4 billion in emergency H1N1 flu vaccine funding (4)? Keep in mind that over 3000 Americans die each month from car accidents (5) and over 3000 die each month from accidental poisonings (6). The National Weather Service reports approximately 400 Americans experience lightning strikes per year (7), so one could argue that Americans are twice as likely to be struck by lightening than their children are likely to die from laboratory confirmed H1N1 viral infection.
Last month, Harvard's School of Public Health in conjunction with the UK Medical Research Council published data confirming that "...the severity of the H1N1 flu may be less than initially feared" with far fewer deaths than the 36,000 that are typical of an average flu season in America (8). In closing, it would be helpful for those of us who sometimes read only the abstract of an important article such as this one to have the source of the data more clearly defined in the abstract. In this case, the majority of the H1N1 data was not derrived from laboratory testing. A better conclusion might be that it is impossible for even the most accomplished medically-trained professors, clinicians, and statisticians to accurately determine the efficacy of a vaccine in terms of lives saved or potential cost savings if we do not insist on more thorough testing of hospitalized patients with ILI during purported pandemics.
1.) Khazeni N, Hutton DW, Garber AM, Hupert N, Owens DK. Effectiveness and cost-effectiveness of vaccination against pandemic influenza (H1N1) 2009. Ann Intern Med. 2009 Dec 15;151(12):829-39. PubMed PMID: 20008759.
5.) http://www.forbes.com/2009/01/21/car-accident-times-forbeslife- cx_he_0121driving.html
7.) http://geology.com/news/2009/numerous-deaths-by-lightning- strikes.shtml
8.) http://www.newsrx.com/print.php?articleID=1715210 Cauchemez S, Donnelly CA, Reed C, Ghani AC, Fraser C, Kent CK, Finelli L, Ferguson NM. Household transmission of 2009 pandemic influenza A (H1N1) virus in the United States. N Engl J Med. 2009 Dec 31;361(27):2619-27.
Khazeni N, Hutton DW, Garber AM, Hupert N, Owens DK. Effectiveness and Cost-Effectiveness of Vaccination Against Pandemic Influenza (H1N1) 2009. Ann Intern Med. 2009;151:829–839. doi: 10.7326/0000605-200912150-00157
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Published: Ann Intern Med. 2009;151(12):829-839.
High Value Care, Infectious Disease, Prevention/Screening, Vaccines/Immunization.
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