Rebekah H. Borse

Estimating the Burden of 2009 Pandemic Influenza A (H1N1) in the United States (April 2009–April 2010)

To calculate the burden of 2009 pandemic influenza A (pH1N1) in the United States, we extrapolated from the Centers for Disease Control and Preventions Emerging Infections Program laboratory-confirmed hospitalizations across the entire United States, and then corrected for underreporting. From 12 April 2009 to 10 April 2010, we estimate that approximately 60.8 million cases (range: 43.3-89.3 million), 274,304 hospitalizations (195,086-402,719), and 12,469 deaths (8868-18,306) occurred in the United States due to pH1N1. Eighty-seven percent of deaths occurred in those under 65 years of age with children and working adults having risks of hospitalization and death 4 to 7 times and 8 to 12 times greater, respectively, than estimates of impact due to seasonal influenza covering the years 1976-2001. In our study, adults 65 years of age or older were found to have rates of hospitalization and death that were up to 75% and 81%, respectively, lower than seasonal influenza. These results confirm the necessity of a concerted public health response to pH1N1.

Effects of Vaccine Program against Pandemic Influenza A(H1N1) Virus, United States, 2009–2010

Vaccination likely prevented 700,000–1,500,000 clinical cases, 4,000–10,000 hospitalizations, and 200–500 deaths.

Estimating Effect of Antiviral Drug Use during Pandemic (H1N1) 2009 Outbreak, United States

From April 2009 through March 2010, during the pandemic (H1N1) 2009 outbreak, ≈8.2 million prescriptions for influenza neuraminidase-inhibiting antiviral drugs were filled in the United States. We estimated the number of hospitalizations likely averted due to use of these antiviral medications. After adjusting for prescriptions that were used for prophylaxis and personal stockpiles, as well as for patients who did not complete their drug regimen, we estimated the filled prescriptions prevented ≈8,400–12,600 hospitalizations (on the basis of median values). Approximately 60% of these prevented hospitalizations were among adults 18–64 years of age, with the remainder almost equally divided between children 0–17 years of age and adults >65 years of age. Public health officials should consider these estimates an indication of success of treating patients during the 2009 pandemic and a warning of the need for renewed planning to cope with the next pandemic.

Closing Schools in Response to the 2009 Pandemic Influenza A H1N1 Virus in New York City: Economic Impact on Households

Understanding the effectiveness of a school closure in limiting social interaction and the economic impact of school closure on households is critical when developing guidelines to prevent spread of pandemic influenza. A New York City survey conducted in June 2009 in 554 households affected by the 2009 pandemic influenza H1N1-related school closures showed that, during closure, 30% of students visited at least 1 locale outside their homes. If all the adults in the home were employed, an ill child was less likely to leave home. In 17% of the households, at least 1 adult missed some work because of the closure. If all adults in the home were employed, someone was more likely to take time off work. If other children were in the household, it was less likely that an adult took time off work. The findings of our study will be important when developing future pandemic school-closure guidance.

Estimating the Potential Effects of a Vaccine Program Against an Emerging Influenza Pandemic—United States

Abstract Background. Human illness from influenza A(H7N9) was identified in March 2013, and candidate vaccine viruses were soon developed. To understand factors that may impact influenza vaccination programs, we developed a model to evaluate hospitalizations and deaths averted considering various scenarios. Methods. We utilized a model incorporating epidemic curves with clinical attack rates of 20% or 30% in a single wave of illness, case hospitalization ratios of 0.5% or 4.2%, and case fatality ratios of 0.08% or 0.53%. We considered scenarios that achieved 80% vaccination coverage, various starts of vaccination programs (16 or 8 weeks before, the same week of, or 8 or 16 weeks after start of pandemic), an administration rate of 10 or 30 million doses per week (the latter rate is an untested assumption), and 2 levels of vaccine effectiveness (2 doses of vaccine required; either 62% or 80% effective for persons aged <60 years, and either 43% or 60% effective for persons aged ≥60 years). Results. The start date of vaccination campaigns most influenced impact; 141 000–2 200 000 hospitalizations and 11 000–281 000 deaths were averted when campaigns started before a pandemic, and <100–1 300 000 hospitalizations and 0–165 000 deaths were averted for programs beginning the same time as or after the introduction of the pandemic virus. The rate of vaccine administration and vaccine effectiveness did not influence campaign impact as much as timing of the start of campaign. Conclusions. Our findings suggest that efforts to improve the timeliness of vaccine production will provide the greatest impacts for future pandemic vaccination programs.

Prevalence of 2009 Pandemic Influenza A (H1N1) Virus Antibodies, Tampa Bay Florida — November–December, 2009

Background In 2009, a novel influenza virus (2009 pandemic influenza A (H1N1) virus (pH1N1)) caused significant disease in the United States. Most states, including Florida, experienced a large fall wave of disease from September through November, after which disease activity decreased substantially. We determined the prevalence of antibodies due to the pH1N1 virus in Florida after influenza activity had peaked and estimated the proportion of the population infected with pH1N1 virus during the pandemic. Methods During November-December 2009, we collected leftover serum from a blood bank, a pediatric childrens hospital and a pediatric outpatient clinic in Tampa Bay Florida. Serum was tested for pH1N1 virus antibodies using the hemagglutination-inhibition (HI) assay. HI titers ≥40 were considered seropositive. We adjusted seroprevalence results to account for previously established HI assay specificity and sensitivity and employed a simple statistical model to estimate the proportion of seropositivity due to pH1N1 virus infection and vaccination. Results During the study time period, the overall seroprevalence in Tampa Bay, Florida was 25%, increasing to 30% after adjusting for HI assay sensitivity and specificity. We estimated that 5.9% of the population had vaccine-induced seropositivity while 25% had seropositivity secondary to pH1N1 virus infection. The highest cumulative incidence of pH1N1 virus infection was among children aged 5–17 years (53%) and young adults aged 18–24 years (47%), while adults aged ≥50 years had the lowest cumulative incidence (11–13%) of pH1N1 virus infection. Conclusions After the peak of the fall wave of the pandemic, an estimated one quarter of the Tampa Bay population had been infected with the pH1N1 virus. Consistent with epidemiologic trends observed during the pandemic, the highest burdens of disease were among school-aged children and young adults.

Modeling the Effect of Water, Sanitation, and Hygiene and Oral Cholera Vaccine Implementation in Haiti

In 2010, toxigenic Vibrio cholerae was newly introduced to Haiti. Because resources are limited, decision-makers need to understand the effect of different preventive interventions. We built a static model to estimate the potential number of cholera cases averted through improvements in coverage in water, sanitation and hygiene (WASH) (i.e., latrines, point-of-use chlorination, and piped water), oral cholera vaccine (OCV), or a combination of both. We allowed indirect effects and non-linear relationships between effect and population coverage. Because there are limited incidence data for endemic cholera in Haiti, we estimated the incidence of cholera over 20 years in Haiti by using data from Malawi. Over the next two decades, scalable WASH interventions could avert 57,949–78,567 cholera cases, OCV could avert 38,569–77,636 cases, and interventions that combined WASH and OCV could avert 71,586–88,974 cases. Rate of implementation is the most influential variable, and combined approaches maximized the effect.

The Economics of Strategies to Reduce Respiratory Syncytial Virus Hospitalizations in Alaska

BACKGROUND Alaska Native infants experience high rates of respiratory syncytial virus (RSV) hospitalizations. Through 2008, Alaska administered a 7-dose (maximum) palivizumab regime to high-risk infants from October to May. In 2009, the maximum was reduced to 3 doses for 32- to 34-week preterm babies and 6 doses for other groups. METHODS We used 11 years of data and regional Medicaid reimbursement rates to model the cost effectiveness of 4 palivizumab intervention strategies to reduce RSV hospitalizations among Alaskan infants including: current strategy, old strategy (1998-2008), and 2 hypothetical strategies using the current strategy plus 1 or 3 doses to all newborn infants during the RSV season. RESULTS The current strategy represents 5 hospitalizations averted per year for the palivizumab cohort (∼50-56 children) at ∼

Efficiency of Points of Dispensing for Influenza A(H1N1)pdm09 Vaccination, Los Angeles County, California, USA, 2009

52 846 per hospitalization averted, compared with no intervention. Compared with the old strategy, the mean cost per hospitalization prevented for the current strategy was 63% lower, net program costs were 85% lower, and the mean hospitalizations prevented were 27% lower. Compared with current strategy only, the addition of 1 dose to all newborns during the RSV season could decrease the mean cost per hospitalization prevented by 23%, increase the number of hospitalizations prevented by 2.5-fold, and increase the net programmatic costs by 3.3-fold; administering up to 3 doses to infants further reduced hospitalizations and increased costs. CONCLUSIONS The current palivizumab strategy improved the cost-effectiveness ratio compared with the old strategy. Further improvement could be obtained by adding doses for Alaskan Native newborns during the RSV season; however, programmatic costs would increase.

Cost-effectiveness of dog rabies vaccination programs in East Africa

During October 23-December 8, 2009, the Los Angeles County Department of Public Health used points of dispensing (PODs) to improve access to and increase the number of vaccinations against influenza A(H1N1)pdm09. We assessed the efficiency of these units and access to vaccines among ethnic groups. An average of 251 persons per hour (SE 65) were vaccinated at the PODs; a 10% increase in use of live-attenuated monovalent vaccines reduced that rate by 23 persons per hour (SE 7). Vaccination rates were highest for Asians (257/10,000 persons), followed by Hispanics (114/10,000), whites (75/100,000), and African Americans (37/10,000). Average distance traveled to a POD was highest for whites (6.6 miles; SD 6.5) and lowest for Hispanics (4.7 miles; SD ±5.3). Placing PODs in areas of high population density could be an effective strategy to reach large numbers of persons for mass vaccination, but additional PODs may be needed to improve coverage for specific populations.