Skip directly to search Skip directly to A to Z list Skip directly to page options Skip directly to site content

Volume 12, Number 1—January 2006

Volume 12, Number 1—January 2006   PDF Version [PDF - 6.97 MB - 189 pages]

THEME ISSUE
Influenza

Overview

  • Influenza Revisited PDF Version [PDF - 30 KB - 2 pages]
    J. K. Taubenberger and D. M. Morens
       
  • H5N1 Outbreaks and Enzootic Influenza PDF Version [PDF - 206 KB - 6 pages]
    R. G. Webster et al.
    View Summary

    Highly pathogenic H5N1 influenza viruses continue to evolve and increase their geographic and host range.

        View Abstract

    Ongoing outbreaks of H5N1 avian influenza in migratory waterfowl, domestic poultry, and humans in Asia during the summer of 2005 present a continuing, protean pandemic threat. We review the zoonotic source of highly pathogenic H5N1 viruses and their genesis from their natural reservoirs. The acquisition of novel traits, including lethality to waterfowl, ferrets, felids, and humans, indicates an expanding host range. The natural selection of nonpathogenic viruses from heterogeneous subpopulations cocirculating in ducks contributes to the spread of H5N1 in Asia. Transmission of highly pathogenic H5N1 from domestic poultry back to migratory waterfowl in western China has increased the geographic spread. The spread of H5N1 and its likely reintroduction to domestic poultry increase the need for good agricultural vaccines. In fact, the root cause of the continuing H5N1 pandemic threat may be the way the pathogenicity of H5N1 viruses is masked by cocirculating influenza viruses or bad agricultural vaccines.

History

  • Influenza Pandemics of the 20th Century PDF Version [PDF - 166 KB - 6 pages]
    E. D. Kilbourne
    View Summary

    Influenza A virus infection created confusion in distinguishing true pandemics, pseudopandemics, and epidemics.

        View Abstract

    Three worldwide (pandemic) outbreaks of influenza occurred in the 20th century: in 1918, 1957, and 1968. The latter 2 were in the era of modern virology and most thoroughly characterized. All 3 have been informally identified by their presumed sites of origin as Spanish, Asian, and Hong Kong influenza, respectively. They are now known to represent 3 different antigenic subtypes of influenza A virus: H1N1, H2N2, and H3N2, respectively. Not classified as true pandemics are 3 notable epidemics: a pseudopandemic in 1947 with low death rates, an epidemic in 1977 that was a pandemic in children, and an abortive epidemic of swine influenza in 1976 that was feared to have pandemic potential. Major influenza epidemics show no predictable periodicity or pattern, and all differ from one another. Evidence suggests that true pandemics with changes in hemagglutinin subtypes arise from genetic reassortment with animal influenza A viruses.

  • 1918 Influenza: the Mother of All Pandemics PDF Version [PDF - 175 KB - 8 pages]
    J. K. Taubenberger and D. M. Morens
        View Abstract

    The "Spanish" influenza pandemic of 1918–1919, which caused ≈50 million deaths worldwide, remains an ominous warning to public health. Many questions about its origins, its unusual epidemiologic features, and the basis of its pathogenicity remain unanswered. The public health implications of the pandemic therefore remain in doubt even as we now grapple with the feared emergence of a pandemic caused by H5N1 or other virus. However, new information about the 1918 virus is emerging, for example, sequencing of the entire genome from archival autopsy tissues. But, the viral genome alone is unlikely to provide answers to some critical questions. Understanding the 1918 pandemic and its implications for future pandemics requires careful experimentation and in-depth historical analysis.

  • Swine Influenza A Outbreak, Fort Dix, New Jersey, 1976 PDF Version [PDF - 98 KB - 6 pages]
    J. C. Gaydos et al.
    View Summary

    Published literature and events surrounding the outbreak are reviewed.

        View Abstract

    In early 1976, the novel A/New Jersey/76 (Hsw1N1) influenza virus caused severe respiratory illness in 13 soldiers with 1 death at Fort Dix, New Jersey. Since A/New Jersey was similar to the 1918–1919 pandemic virus, rapid outbreak assessment and enhanced surveillance were initiated. A/New Jersey virus was detected only from January 19 to February 9 and did not spread beyond Fort Dix. A/Victoria/75 (H3N2) spread simultaneously, also caused illness, and persisted until March. Up to 230 soldiers were infected with the A/New Jersey virus. Rapid recognition of A/New Jersey, swift outbreak assessment, and enhanced surveillance resulted from excellent collaboration between Fort Dix, New Jersey Department of Health, Walter Reed Army Institute of Research, and Center for Disease Control personnel. Despite efforts to define the events at Fort Dix, many questions remain unanswered, including the following: Where did A/New Jersey come from? Why did transmission stop?

  • Reflections on the 1976 Swine Flu Vaccination Program PDF Version [PDF - 38 KB - 5 pages]
    D. J. Sencer and J. Millar
    View Summary

    The swine flu vaccination program has implications for the current pandemic preparedness.

        View Abstract

    In 1976, 2 recruits at Fort Dix, New Jersey, had an influenzalike illness. Isolates of virus taken from them included A/New Jersey/76 (Hsw1n1), a strain similar to the virus believed at the time to be the cause of the 1918 pandemic, commonly known as swine flu. Serologic studies at Fort Dix suggested that >200 soldiers had been infected and that person-to-person transmission had occurred. We review the process by which these events led to the public health decision to mass-vaccinate the American public against the virus and the subsequent events that led to the program's cancellation. Observations of policy and implementation success and failures are presented that could help guide decisions regarding avian influenza.

  • Influenza Pandemic Periodicity, Virus Recycling, and the Art of Risk Assessment PDF Version [PDF - 123 KB - 6 pages]
    W. R. Dowdle
    View Summary

    Conditions that lead to influenza pandemics are not fully understood.

        View Abstract

    Influenza pandemic risk assessment is an uncertain art. The theory that influenza A virus pandemics occur every 10 to 11 years and seroarcheologic evidence of virus recycling set the stage in early 1976 for risk assessment and risk management of the Fort Dix, New Jersey, swine influenza outbreak. Additional data and passage of time proved the theory untenable. Much has been learned about influenza A virus and its natural history since 1976, but the exact conditions that lead to the emergence of a pandemic strain are still unknown. Current avian influenza events parallel those of swine influenza in 1976 but on a larger and more complex scale. Pre- and postpandemic risk assessment and risk management are continuous but separate public health functions.

  • The Swine Flu Episode and the Fog of Epidemics PDF Version [PDF - 131 KB - 4 pages]
    R. Krause
    View Summary

    Knowledge of the 1976 swine flu episode can help shape public health response to future pandemic threats.

        View Abstract

    The 1918 influenza pandemic has shaped research and public health for nearly a century. In 1976, the specter of 1918 loomed large when a pandemic threatened the country again. Public health officials initiated a mass vaccination campaign, but the anticipated pandemic failed to occur. An examination of the available data in 1976 and the decision to vaccinate, as well as lessons learned from the HIV/AIDS epidemic in the early 1980s, may help shape an appropriate public health response to future threats from avian influenza or other infectious diseases.

Pathogenesis

  • Antiviral Response in Pandemic Influenza Viruses PDF Version [PDF - 36 KB - 4 pages]
    A. García-Sastre
    View Summary

    The regulatory activities of the nonstructural protein 1 appear to affect the ability of influenza viruses to infect multiple animal species.

        View Abstract

    The outcome of viral infections depends on a complex set of interactions between the viruses and their hosts. Particularly, viral infection triggers specific signaling programs within the infected cells that results in substantial changes in host gene expression. While some of these changes might be beneficial for viral replication, others represent the induction of a host antiviral response. In this respect, viruses have evolved genes that counteract this initial innate antiviral response. These viral-host interactions shape the subsequent phases of the disease and influence the adaptive immune response. In influenza viruses, the nonstructural protein 1 inhibits the interferon-mediated antiviral response. The regulatory activities of this viral protein play a major role in the pathogenicity of influenza virus and appear partially responsible for the ability of influenza viruses to infect multiple animal species, which likely contributes to the generation of new pandemic viruses in humans.

  • Cell-mediated Protection in Influenza Infection PDF Version [PDF - 103 KB - 7 pages]
    P. G. Thomas et al.
    View Summary

    Cell-mediated immune responses should be considered in vaccination protocols.

        View Abstract

    Current vaccine strategies against influenza focus on generating robust antibody responses. Because of the high degree of antigenic drift among circulating influenza strains over the course of a year, vaccine strains must be reformulated specifically for each influenza season. The time delay from isolating the pandemic strain to large-scale vaccine production would be detrimental in a pandemic situation. A vaccine approach based on cell-mediated immunity that avoids some of these drawbacks is discussed here. Specifically, cell-mediated responses typically focus on peptides from internal influenza proteins, which are far less susceptible to antigenic variation. We review the literature on the role of CD4+ and CD8+ T cell–mediated immunity in influenza infection and the available data on the role of these responses in protection from highly pathogenic influenza infection. We discuss the advantages of developing a vaccine based on cell-mediated immune responses toward highly pathogenic influenza virus and potential problems arising from immune pressure.

Prevention

  • Vaccines and Antiviral Drugs in Pandemic Preparedness PDF Version [PDF - 77 KB - 6 pages]
    A. S. Monto
    View Summary

    Controlling a pandemic with vaccine and antiviral drugs will require a coordinated international approach to determine how the least amount of virus can immunize the largest segment of a population.

        View Abstract

    While measures such as closing schools and social distancing may slow the effects of pandemic influenza, only vaccines and antiviral drugs are clearly efficacious in preventing infection or treating illness. Unless the pandemic strain closely resembles one already recognized, vaccine will not be available early. However, studies can be conducted beforehand to address questions concerning vaccine dose, frequency of inoculation, and need for adjuvants. In contrast, antiviral drugs, particularly the neuraminidase inhibitors, will be effective for treatment and available if stockpiling takes place. Special questions need to be answered if a highly lethal virus, such as influenza A (H5N1), produces the pandemic. Both vaccines and antiviral drugs will be required for a coordinated strategy.

  • Making Better Influenza Virus Vaccines? PDF Version [PDF - 58 KB - 5 pages]
    P. Palese
    View Summary

    Better influenza vaccines are possible and necessary.

        View Abstract

    Killed and live influenza virus vaccines are effective in preventing and curbing the spread of disease, but new technologies such as reverse genetics could be used to improve them and to shorten the lengthy process of preparing vaccine seed viruses. By taking advantage of these new technologies, we could develop live vaccines that would be safe, cross-protective against variant strains, and require less virus per dose than conventional vaccines. Furthermore, pandemic vaccines against highly virulent strains such as the H5N1 virus can only be generated by reverse genetics techniques. Other technologic breakthroughs should result in effective adjuvants for use with killed and live vaccines, increasing the number of available doses. Finally, universal influenza virus vaccines seem to be within reach. These new strategies will be successful if they are supported by regulatory agencies and if a robust market for influenza virus vaccines against interpandemic and pandemic threats is made and sustained.

  • Vaccines for Pandemic Influenza PDF Version [PDF - 157 KB - 7 pages]
    C. J. Luke and K. Subbarao
    View Summary

    A program to develop vaccines to prevent avian influenza pandemics is under way.Vaccines for Pandemic Influenza

        View Abstract

    Recent outbreaks of highly pathogenic avian influenza in Asia and associated human infections have led to a heightened level of awareness and preparation for a possible influenza pandemic. Vaccination is the best option by which spread of a pandemic virus could be prevented and severity of disease reduced. Production of live attenuated and inactivated vaccine seed viruses against avian influenza viruses, which have the potential to cause pandemics, and their testing in preclinical studies and clinical trials will establish the principles and ensure manufacturing experience that will be critical in the event of the emergence of such a virus into the human population. Studies of such vaccines will also add to our understanding of the biology of avian influenza viruses and their behavior in mammalian hosts.

  • Pandemic Influenza Threat and Preparedness PDF Version [PDF - 89 KB - 5 pages]
    A. S. Fauci
    View Summary

    New vaccine technologies and antiviral drugs are needed to prepare for the next influenza pandemic.

        View Abstract

    The threat of a human influenza pandemic has greatly increased over the past several years with the emergence of highly virulent avian influenza viruses, notably H5N1 viruses, which have infected humans in several Asian and European countries. Previous influenza pandemics have arrived with little or no warning, but the current widespread circulation of H5N1 viruses among avian populations and their potential for increased transmission to humans and other mammalian species may afford us an unprecedented opportunity to prepare for the next pandemic threat. The US Department of Health and Human Services is coordinating a national strategy to respond to an influenza pandemic that involves multiple agencies, including the Centers for Disease Control and Prevention, the Food and Drug Administration, and the National Institutes of Health (NIH). Within NIH, the National Institute of Allergy and Infectious Diseases (NIAID) conducts basic and clinical research to develop new vaccine technologies and antiviral drugs against influenza viruses. We describe recent research progress in preparing for pandemic influenza.

Another Dimension

Volume 12, Number 1—January 2006 - Continued

Research

  • Economics of Neuraminidase Inhibitor Stockpiling for Pandemic Influenza, Singapore PDF Version [PDF - 263 KB - 8 pages]
    V. J. Lee et al.
    View Summary

    Stockpiling drugs to prevent and treat influenza would be economically effective.

        View Abstract

    We compared strategies for stockpiling neuraminidase inhibitors to treat and prevent influenza in Singapore. Cost-benefit and cost-effectiveness analyses, with Monte Carlo simulations, were used to determine economic outcomes. A pandemic in a population of 4.2 million would result in an estimated 525–1,775 deaths, 10,700–38,600 hospitalization days, and economic costs of $0.7 to $2.2 billion Singapore dollars. The treatment-only strategy had optimal economic benefits: stockpiles of antiviral agents for 40% of the population would save an estimated 418 lives and $414 million, at a cost of $52.6 million per shelf-life cycle of the stockpile. Prophylaxis was economically beneficial in high-risk subpopulations, which account for 78% of deaths, and in pandemics in which the death rate was >0.6%. Prophylaxis for pandemics with a 5% case-fatality rate would save 50,000 lives and $81 billion. These models can help policymakers weigh the options for pandemic planning.

  • Estimating Influenza Hospitalizations among Children PDF Version [PDF - 121 KB - 7 pages]
    C. G. Grijalva et al.
    View Summary

    Two surveillance systems gave a better estimate of influenza hospitalizations in children <5 years of age than either system alone.

        View Abstract

    Although influenza causes more hospitalizations and deaths among American children than any other vaccine-preventable disease, deriving accurate population-based estimates of disease impact is challenging. Using 2 independent surveillance systems, we performed a capture-recapture analysis to estimate influenza-associated hospitalizations in children in Davidson County, Tennessee, during the 2003–2004 influenza season. The New Vaccine Surveillance Network (NVSN) enrolled children hospitalized with respiratory symptoms or fever and tested them for influenza. The Tennessee Emerging Infections Program (EIP) identified inpatients with positive influenza diagnostic test results through review of laboratory and infection control logs. The hospitalization rate estimated from the capture-recapture analysis in children <5 years of age was 2.4 per 1,000 (95% confidence interval 1.8–3.8). When NVSN estimates were compared with capture-recapture estimates, NVSN found 84% of community-acquired cases, EIP found 64% of cases in which an influenza rapid test was performed, and the overall sensitivity of NVSN and EIP for influenza hospitalizations was 73% and 38%, respectively.

  • Real-time Estimates in Early Detection of SARS PDF Version [PDF - 167 KB - 4 pages]
    S. Cauchemez et al.
    View Summary

    A statistical method can be used for early monitoring of the effect of disease control measures.

        View Abstract

    We propose a Bayesian statistical framework for estimating the reproduction number R early in an epidemic. This method allows for the yet-unrecorded secondary cases if the estimate is obtained before the epidemic has ended. We applied our approach to the severe acute respiratory syndrome (SARS) epidemic that started in February 2003 in Hong Kong. Temporal patterns of R estimated after 5, 10, and 20 days were similar. Ninety-five percent credible intervals narrowed when more data were available but stabilized after 10 days. Using simulation studies of SARS-like outbreaks, we have shown that the method may be used for early monitoring of the effect of control measures.

  • Influenza-associated Deaths in Tropical Singapore PDF Version [PDF - 224 KB - 8 pages]
    A. Chow et al.
    View Summary

    Surveillance and annual vaccination are needed for at-risk populations in tropical countries.

        View Abstract

    We used a regression model to examine the impact of influenza on death rates in tropical Singapore for the period 1996–2003. Influenza A (H3N2) was the predominant circulating influenza virus subtype, with consistently significant and robust effect on mortality rates. Influenza was associated with an annual death rate from all causes, from underlying pneumonia and influenza, and from underlying circulatory and respiratory conditions of 14.8 (95% confidence interval 9.8–19.8), 2.9 (1.0–5.0), and 11.9 (8.3–15.7) per 100,000 person-years, respectively. These results are comparable with observations in the United States and subtropical Hong Kong. An estimated 6.5% of underlying pneumonia and influenza deaths were attributable to influenza. The proportion of influenza-associated deaths was 11.3 times higher in persons age >65 years than in the general population. Our findings support the need for influenza surveillance and annual influenza vaccination for at-risk populations in tropical countries.

  • Real-time Forecast of Multiphase Outbreak PDF Version [PDF - 273 KB - 6 pages]
    Y. Hsieh and Y. Cheng
    View Summary

    The multistage Richards model provides insights into ongoing outbreaks that may be useful for real-time public health responses.

        View Abstract

    We used a single equation with discrete phases to fit the daily cumulative case data from the 2003 severe acute respiratory syndrome outbreak in Toronto. This model enabled us to estimate turning points and case numbers during the 2 phases of this outbreak. The 3 estimated turning points are March 25, April 27, and May 24. The estimated case number during the first phase of the outbreak between February 23 and April 26 is 140.53 (95% confidence interval [CI] 115.88–165.17) if we use the data from February 23 to April 4; and 249 (95% CI: 246.67–251.25) at the end of the second phase on June 12 if we use the data from April 28 to June 4. The second phase can be detected by using case data just 3 days past the beginning of the phase, while the first and third turning points can be identified only ≈10 days afterwards. Our modeling procedure provides insights into ongoing outbreaks that may facilitate real-time public health responses.

  • SARS–associated Coronavirus Replication in Cell Lines PDF Version [PDF - 360 KB - 6 pages]
    M. Kaye et al.
    View Summary

    Virus can replicate in several common cell lines, sometimes without cytopathic effect.

        View Abstract

    Given the potential for laboratory-associated severe acute respiratory syndrome–associated coronavirus (SARS-CoV) infections, we must know which cell lines are susceptible to the virus. We investigated 21 cell lines routinely used for virus isolation or research. After infection with SARS-CoV, cells were observed for cytopathic effects, and quantitative real-time polymerase chain reaction was used to measure ongoing viral replication. An indirect immunofluorescence assay was also used as a confirmatory test. The study identified 10 new cell lines capable of supporting the replication of SARS-CoV and confirmed the susceptibility of 4 cell lines previously reported. This study shows that SARS-CoV can be isolated in several cell lines commonly used for diagnostic or research purposes. It also shows that SARS-CoV can achieve high titers in several cell lines, sometimes in the absence of specific cytopathic effects.

Policy Review

  • Nonpharmaceutical Interventions for Pandemic Influenza, International Measures PDF Version [PDF - 174 KB - 7 pages]
    View Summary

    Closing international borders was usually ineffective in past pandemics and would be less effective today.

        View Abstract

    Since global availability of vaccine and antiviral agents against influenza caused by novel human subtypes is insufficient, the World Health Organization (WHO) recommends nonpharmaceutical public health interventions to contain infection, delay spread, and reduce the impact of pandemic disease. Virus transmission characteristics will not be completely known in advance, but difficulties in influenza control typically include peak infectivity early in illness, a short interval between cases, and to a lesser extent, transmission from persons with incubating or asymptomatic infection. Screening and quarantining entering travelers at international borders did not substantially delay virus introduction in past pandemics, except in some island countries, and will likely be even less effective in the modern era. Instead, WHO recommends providing information to international travelers and possibly screening travelers departing countries with transmissible human infection. The principal focus of interventions against pandemic influenza spread should be at national and community levels rather than international borders.

  • Nonpharmaceutical Interventions for Pandemic Influenza, National and Community Measures PDF Version [PDF - 199 KB - 7 pages]
    View Summary

    Recommended interventions vary by transmission pattern, pandemic phase, and disease severity.

        View Abstract

    The World Health Organization's recommended pandemic influenza interventions, based on limited data, vary by transmission pattern, pandemic phase, and illness severity and extent. In the pandemic alert period, recommendations include isolation of patients and quarantine of contacts, accompanied by antiviral therapy. During the pandemic period, the focus shifts to delaying spread and reducing effects through population-based measures. Ill persons should remain home when they first become symptomatic, but forced isolation and quarantine are ineffective and impractical. If the pandemic is severe, social distancing measures such as school closures should be considered. Nonessential domestic travel to affected areas should be deferred. Hand and respiratory hygiene should be routine; mask use should be based on setting and risk, and contaminated household surfaces should be disinfected. Additional research and field assessments during pandemics are essential to update recommendations. Legal authority and procedures for implementing interventions should be understood in advance and should respect cultural differences and human rights.

Dispatches

Letters

Books and Media

About the Cover

Etymologia

Conference Summaries

TOP