National Academies Press: OpenBook
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×

FRAMEWORK FOR

EQUITABLE

ALLOCATION OF

COVID-19

VACCINE

Helene Gayle, William Foege, Lisa Brown, and Benjamin Kahn, Editors

Committee on Equitable Allocation of Vaccine for the Novel
Coronavirus

Board on Health Sciences Policy

Board on Population Health and Public Health Practice

Health and Medicine Division

A Consensus Study Report of

images

and

NATIONAL ACADEMY OF MEDICINE

THE NATIONAL ACADEMIES PRESS
Washington, DC
www.nap.edu

Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×

THE NATIONAL ACADEMIES PRESS 500 Fifth Street, NW Washington, DC 20001

This activity was supported by contracts between the National Academy of Sciences and the Centers for Disease Control and Prevention and the National Institutes of Health (HHSN263201800029I). This project has been funded in whole or in part with federal funds from the Office of Science Policy, National Institutes of Health, U.S. Department of Health and Human Services under Contract No. HHSN263201800029I. Any opinions, findings, conclusions, or recommendations expressed in this publication do not necessarily reflect the views of any organization or agency that provided support for the project.

International Standard Book Number-13: 978-0-309-68224-4
International Standard Book Number-10: 0-309-68224-X
Digital Object Identifier: https://doi.org/10.17226/25917
Library of Congress Control Number: 2020947136

Additional copies of this publication are available from the National Academies Press, 500 Fifth Street, NW, Keck 360, Washington, DC 20001; (800) 624-6242 or (202) 334-3313; http://www.nap.edu.

Copyright 2020 by the National Academy of Sciences. All rights reserved.

Printed in the United States of America

Suggested citation: National Academies of Sciences, Engineering, and Medicine. 2020. Framework for equitable allocation of COVID-19 vaccine. Washington, DC: The National Academies Press. https://doi.org/10.17226/25917.

Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×

Image

The National Academy of Sciences was established in 1863 by an Act of Congress, signed by President Lincoln, as a private, nongovernmental institution to advise the nation on issues related to science and technology. Members are elected by their peers for outstanding contributions to research. Dr. Marcia McNutt is president.

The National Academy of Engineering was established in 1964 under the charter of the National Academy of Sciences to bring the practices of engineering to advising the nation. Members are elected by their peers for extraordinary contributions to engineering. Dr. John L. Anderson is president.

The National Academy of Medicine (formerly the Institute of Medicine) was established in 1970 under the charter of the National Academy of Sciences to advise the nation on medical and health issues. Members are elected by their peers for distinguished contributions to medicine and health. Dr. Victor J. Dzau is president.

The three Academies work together as the National Academies of Sciences, Engineering, and Medicine to provide independent, objective analysis and advice to the nation and conduct other activities to solve complex problems and inform public policy decisions. The National Academies also encourage education and research, recognize outstanding contributions to knowledge, and increase public understanding in matters of science, engineering, and medicine.

Learn more about the National Academies of Sciences, Engineering, and Medicine at www.nationalacademies.org.

Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×

Image

Consensus Study Reports published by the National Academies of Sciences, Engineering, and Medicine document the evidence-based consensus on the study’s statement of task by an authoring committee of experts. Reports typically include findings, conclusions, and recommendations based on information gathered by the committee and the committee’s deliberations. Each report has been subjected to a rigorous and independent peer-review process and it represents the position of the National Academies on the statement of task.

Proceedings published by the National Academies of Sciences, Engineering, and Medicine chronicle the presentations and discussions at a workshop, symposium, or other event convened by the National Academies. The statements and opinions contained in proceedings are those of the participants and are not endorsed by other participants, the planning committee, or the National Academies.

For information about other products and activities of the National Academies, please visit www.nationalacademies.org/about/whatwedo.

Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×

COMMITTEE ON EQUITABLE ALLOCATION OF VACCINE FOR THE NOVEL CORONAVIRUS

WILLIAM H. FOEGE (Co-Chair), Emeritus Distinguished Professor of International Health, Rollins School of Public Health, Emory University

HELENE D. GAYLE (Co-Chair), President and Chief Executive Officer, The Chicago Community Trust

MARGARET L. BRANDEAU, Coleman F. Fung Professor of Engineering, Professor of Medicine (by courtesy), Department of Management Science and Engineering, Stanford University

ALISON M. BUTTENHEIM, Associate Professor of Nursing and Health Policy, University of Pennsylvania School of Nursing

R. ALTA CHARO, Warren P. Knowles Professor of Law and Bioethics, University of Wisconsin Law School

JAMES F. CHILDRESS, University Professor Emeritus, Institute for Practical Ethics and Public Life, University of Virginia

ANA V. DIEZ ROUX, Dean and Distinguished University Professor of Epidemiology, Dornsife School of Public Health, Drexel University

ABIGAIL ECHO-HAWK (Citizen of the Pawnee Nation), Director, Urban Indian Health Institute, Chief Research Officer, Seattle Indian Health Board

CHRISTOPHER ELIAS, President, Global Development Division, Bill & Melinda Gates Foundation

BARUCH FISCHHOFF, Howard Heinz University Professor, Department of Engineering and Public Policy, Institute for Politics and Strategy, Carnegie Mellon University

DAVID MICHAELS, Professor, Environmental and Occupational Health, Milken Institute School of Public Health, The George Washington University

JEWEL MULLEN, Associate Dean for Health Equity, Associate Professor of Population Health and Internal Medicine, The University of Texas at Austin Dell Medical School

SAAD B. OMER, Director, Yale Institute for Global Health

DANIEL POLSKY, Bloomberg Distinguished Professor of Health Policy and Economics, Carey Business School and Bloomberg School of Public Health, Johns Hopkins University

SONJA A. RASMUSSEN, Professor of Pediatrics, Epidemiology, and Obstetrics and Gynecology, College of Medicine and College of Public Health and Health Professions, University of Florida

Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×

ARTHUR L. REINGOLD, Division Head, Epidemiology and Biostatistics, Professor of Epidemiology, School of Public Health, University of California, Berkeley

REED V. TUCKSON, Managing Director, Tuckson Health Connections, LLC

MICHAEL R. WASSERMAN, President, California Association of Long Term Care Medicine

Study Staff

LISA BROWN, Study Director

BENJAMIN KAHN, Associate Program Officer

ELIZABETH FINKELMAN, Senior Program Officer

AURELIA ATTAL-JUNCQUA, Associate Program Officer

EMMA FINE, Associate Program Officer

REBECCA CHEVAT, Senior Program Assistant

ROSE MARIE MARTINEZ, Senior Director, Board on Population Health and Public Health Practice

ANDREW M. POPE, Senior Director, Board on Health Sciences Policy

Science Writer

ANNA NICHOLSON

Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×

Reviewers

This Consensus Study Report was reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise. The purpose of this independent review is to provide candid and critical comments that will assist the National Academies of Sciences, Engineering, and Medicine in making each published report as sound as possible and to ensure that it meets the institutional standards for quality, objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process.

We thank the following individuals for their review of this report:

Page viii Cite
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×

In addition, we again thank the reviewers who provided comments on the Discussion Draft of the Preliminary Framework for Equitable Allocation of COVID-19 Vaccine, some of whom also served as reviewers for this report:

Although the reviewers listed above provided many constructive comments and suggestions, they were not asked to endorse the conclusions or recommendations of this report nor did they see the final draft before its release. The review of this report was overseen by BRUCE N. CALONGE, The Colorado Trust, ELLEN WRIGHT CLAYTON, Vanderbilt University Medical Center, and SUSAN J. CURRY, The University of Iowa. They were responsible for making certain that an independent examination of this report was carried out in accordance with the standards of the National Academies and that all review comments were carefully considered. Responsibility for the final content rests entirely with the authoring committee and the National Academies.

Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×

This page intentionally left blank.

Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×

Acronyms and Abbreviations

AAP American Academy of Pediatrics
ACA Patient Protection and Affordable Care Act
ACIP Advisory Committee on Immunization Practices
ACT-A Access to COVID Tools (ACT) Accelerator
ADI Area Deprivation Index
AI/AN American Indian/Alaska Native
AMC advanced market commitment
 
BeSD behavioral and social drivers of vaccination
BMI body mass index
   
CARES Coronavirus Aid, Relief, and Economic Security
CCVI COVID-19 Community Vulnerability Index
CDC Centers for Disease Control and Prevention
CEPI Coalition for Epidemic Preparedness Innovations
CMS Centers for Medicare & Medicaid Services
COVID-19 coronavirus disease 2019
COVID-NET COVID-19 Associated Hospitalization Surveillance Network
CSC crisis standards of care
   
DHS U.S. Department of Homeland Security
DoD U.S. Department of Defense
   
EMS emergency medical services
EU European Union
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
EUA Emergency Use Authorization
   
FDA U.S. Food and Drug Administration
   
GPMB Global Preparedness Monitoring Board
   
HHS U.S. Department of Health and Human Services
HMD Health and Medicine Division
   
ICU intensive care unit
IHR International Health Regulations
IHS Indian Health Service
IOM Institute of Medicine
   
LGBTQ+ lesbian, gay, bisexual, transgender, queer, and others
   
MCM medical countermeasure
mRNA messenger RNA
   
NAM National Academy of Medicine
n.d. no date
NIAID National Institute of Allergy and Infectious Diseases
NIH National Institutes of Health
   
OSHA Occupational Safety and Health Administration
OWS Operation Warp Speed
   
PHEP public health emergency preparedness
PPE personal protective equipment
PREP Public Readiness and Emergency Preparedness
   
SAGE Strategic Advisory Group of Experts
SARS severe acute respiratory syndrome
SARS-CoV-2 SARS coronavirus 2
STLT state, tribal, local, and territorial
SVI Social Vulnerability Index
   
VTrckS Vaccine Tracking System
   
WHO World Health Organization
Page xvii Cite
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×

Preface

“Certainty,” Richard Feynman said, “is the Achilles heel of science.” We approach this task with humbleness and great uncertainty. At the time of this writing, we do not know when a vaccine for coronavirus disease 2019 (COVID-19) will pass Phase III studies or will be licensed by the U.S. Food and Drug Administration. Even then, we will not know the effectiveness of the vaccine in protecting the very old or the very young. If protective, we do not know the duration of protection. We do not know what will constitute primary immunization or the need for boosters, and we do not know if rare but potentially serious adverse events will occur, and, if so, in which groups.

We do not understand the nuances of virus spread. What increases the risk of acquisition and transmission? How long does immunity last? How rare or frequent is reinfection? Are there preventive measures beyond masks, hand washing, social distancing, minimizing size of groups, and improving indoor air quality, not yet defined?

How will a vaccine change the equation given the hesitancy expressed by many? How can risk categories be established that account for both personal and social vulnerabilities? What is the chance of a virus mutation that puts all of the investments in vaccine production at risk?

In addition to these scientific uncertainties, we approached this task in the face of gaps and conflicts in legal authority and unprecedented economic and political uncertainty. The Centers for Disease Control and Prevention and the National Institutes of Health understood such uncertainties but also understood the urgency of having guidance ready when a safe and effective vaccine becomes available. As such, these two agencies asked

Page xviii Cite
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×

the National Academies of Sciences, Engineering, and Medicine to make recommendations on the equitable allocation of a COVID-19 vaccine by assembling the best recommendations from scientists, ethicists, psychologists, epidemiologists, and others using the latest information available. Despite an intense effort, this framework should still be regarded as an evolving document—meant to be adapted and refined by its implementers in the face of continuing improvement in our understanding of the dynamics of the pandemic.

In embarking on our task, the committee started with equity. Inequity has been a hallmark of this pandemic, both locally and globally. Inequities in health have always existed, but at this moment there is an awakening to the power of racism, poverty, and bias in amplifying the health and economic pain and hardship imposed by this pandemic. Thus, we saw our work as one way to address these wrongs and do our part to work toward a new commitment to promoting health equity that is informed by but lives beyond this moment.

The committee then approached what the science reveals about transmission, susceptibility, and risks of severe disease or death. The committee decided that a single objective, even one as important as mortality, obscures the impact of this virus on the triad of suffering, death, and societal dysfunction. Therefore, a target of reducing all three seemed appropriate.

Nobel Laureate Albert Schweitzer reminded us that suffering can often be a greater burden than death itself. The increase in poverty, the cost of isolation, and the inability to work or to be forced to work in unsafe environments have led to mental as well as physical suffering of major proportions.

The proposal of phases versus the usual nomenclature of tiers may appear to be insignificant or artificial. But, it seemed more dynamic, indicates movement, and eliminates the suggestion of any group having greater importance. It asserts that all life has equal value but also allows for the importance of making timing decisions about a potentially scarce resource.

In the end, the real work will be done in states, localities, and tribal lands. It should use every lesson we have learned in getting vaccine to both children and adults. It should use the experience of a system that eliminated polio from this country and stopped measles transmission for long periods of time. It should use the commercial delivery systems that worked so well during the H1N1 outbreak. It should use every health worker and volunteer needed to make this a successful community and national effort.

A report by a National Academies committee is not the same as effectively getting a message to the public.1 It does not vaccinate a single

___________________

1 Bloom, B. R., G. J. Nowak, and W. Orenstein. 2020. “When will we have a vaccine?”—understanding questions and answers about COVID-19 vaccination. The New England Journal of Medicine. September 8, 2020. doi: 10.1056/NEJMp2025331.

Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×

person. But, it can provide guidelines and be the impetus for one of the most consequential peacetime efforts this country has ever seen as well as a springboard to resuming our place as a leader in global health.

“First, do no harm,” is repeated endlessly in medical education. We do far more harm, and kill far more people, by our errors of omission, rather than by our errors of commission. It is the science not shared, the vaccine not provided, the assistance not given, that results in suffering in other countries. We have a chance to protect ourselves and to be a leader in protecting the rest of the world. It is a challenge worthy of this country.

Lastly, we want to say what a privilege, honor, and joy it has been to work with this committee and staff. The dedication to purpose and the esprit de corps that developed was impressive and heartening. It is exactly this kind of effort and selflessness that is needed to address a pandemic effectively, and this group definitely rose to the occasion. Thank you to Victor Dzau for his leadership and support throughout this activity. Thanks to Rose Marie Martinez and Andrew Pope for providing daily guidance in preparing a useful report. Special recognition goes to the staff; in particular, we note that Lisa Brown and Benjamin Kahn gave their all to support the committee process and writing of the report. They were tireless, thoughtful, and always pleasant despite the fact that “there are no weekends in a pandemic.” Elizabeth Finkelman, Aurelia Attal-Juncqua, Emma Fine, and Rebecca Chevat rounded out the staff support and provided extensive assistance in the research and development of the report. What a joy it has been to work with such talented staff and committee members.

Helene D. Gayle, Co-Chair
William H. Foege, Co-Chair
Committee on Equitable Allocation of Vaccine for the Novel Coronavirus

Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×

This page intentionally left blank.

Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Page R1
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Page R2
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Page R3
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Page R4
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Page R5
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Page R6
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Page R7
Page viii Cite
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Page R8
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Page R9
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Page R10
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Page R11
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Page R12
Page xiii Cite
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Page R13
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Page R14
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Page R15
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Page R16
Page xvii Cite
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Page R17
Page xviii Cite
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Page R18
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Page R19
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2020. Framework for Equitable Allocation of COVID-19 Vaccine. Washington, DC: The National Academies Press. doi: 10.17226/25917.
×
Page R20
Next: Summary »
Framework for Equitable Allocation of COVID-19 Vaccine Get This Book
×
 Framework for Equitable Allocation of COVID-19 Vaccine
Buy Paperback | $65.00 Buy Ebook | $54.99
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

In response to the coronavirus disease 2019 (COVID-19) pandemic and the societal disruption it has brought, national governments and the international community have invested billions of dollars and immense amounts of human resources to develop a safe and effective vaccine in an unprecedented time frame. Vaccination against this novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), offers the possibility of significantly reducing severe morbidity and mortality and transmission when deployed alongside other public health strategies and improved therapies.

Health equity is intertwined with the impact of COVID-19 and there are certain populations that are at increased risk of severe illness or death from COVID-19. In the United States and worldwide, the pandemic is having a disproportionate impact on people who are already disadvantaged by virtue of their race and ethnicity, age, health status, residence, occupation, socioeconomic condition, or other contributing factors.

Framework for Equitable Allocation of COVID-19 Vaccine offers an overarching framework for vaccine allocation to assist policy makers in the domestic and global health communities. Built on widely accepted foundational principles and recognizing the distinctive characteristics of COVID-19, this report's recommendations address the commitments needed to implement equitable allocation policies for COVID-19 vaccine.

READ FREE ONLINE

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    Switch between the Original Pages, where you can read the report as it appeared in print, and Text Pages for the web version, where you can highlight and search the text.

    « Back Next »
  6. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  7. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  8. ×

    View our suggested citation for this chapter.

    « Back Next »
  9. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!