In Nigeria, a cluster of Ebola cases in July 2014 resulted from a traveler from Liberia. CDC deployed disease control experts to Lagos, the country’s most populous city, within 72 hours and, in the first week after disease confirmation, supplemented response efforts with 13 Field Epidemiology Training Program (FETP) trainees, graduates, and trainers who had experience in epidemiology and infection control. In the 2 weeks that followed, CDC sent additional agency staff and helped mobilize 40 CDC-trained physicians from Nigeria’s FETP. With the Nigerian government and partners, CDC facilitated creation of an effective incident management system, using leadership and staff from the Nigerian Polio Eradication Program and support from the Bill and Melinda Gates Foundation. This incident management system oversaw training of 2,300 health care staff, creation of an ETU in 14 days, and identification of >800 contacts; conducted 19,000 home visits of these contacts to monitor symptoms and temperatures; and screened >150,000 persons at airports. Although 19 secondary cases of Ebola occurred in 3 generations of spread in 2 cities, this rapid action controlled transmission, and Nigeria has been Ebola-free since this incident (3).

CDC staff provided similar assistance in Mali after a child arriving from Guinea died of Ebola and again after a cluster of cases occurred from a person from the Mali–Guinea border who had previously undiagnosed Ebola (29), and in Senegal after an incident of disease importation (4). CDC also collaborated with WHO to increase preparedness in at-risk countries by helping establish EOCs, surveillance for hemorrhagic fever and clusters of deaths, training in contact tracing, laboratory specimen transport and testing, isolation capacity for patients suspected of having Ebola, health communication messages, and border health security.

Before diagnosis of the first case of Ebola imported to the United States, CDC alerted US health care providers to consider Ebola if compatible signs and symptoms manifested within 21 days after a traveler arrived from an affected country (30). CDC also issued infection control guidance for hospitals (31); strengthened laboratory networks and existing surveillance systems; and disseminated recommendations for travelers on the CDC website, through social media channels, and at US international airports.

The first case of Ebola diagnosed in the United States, imported by a traveler from Liberia, revealed gaps in hospital preparedness and response capabilities (32). Ebola was not considered in the patient’s initial presentation, despite fever and travel history to Liberia. CDC provided assistance to the state and local health departments and to nearby hospitals. Two nurses caring for the patient were infected, most likely as the result of underprepared processes, lack of training, and suboptimal use of PPE during the first few days of the patient’s second hospitalization, before his Ebola diagnosis. CDC subsequently strengthened recommendations for infection control, particularly training, supervision, and specifications of PPE. The second nurse who became ill was allowed to travel by air despite exposure that CDC should have categorized as high-risk to prevent the nurse from flying (33). In turn, this measure would have reduced the number of travelers whose health was monitored and the work of public health personnel monitoring contacts.

Recognizing a need for enhanced preparedness and training, CDC staff then visited 81 facilities in 21 states and Washington, DC, helping 55 of these facilities qualify as Ebola Treatment Centers for patients with suspected or confirmed Ebola. CDC also has qualified 56 state, county, and local public health laboratories to perform real-time quantitative reverse transcription PCR for Ebola with a Food and Drug Administration–approved DoD assay developed by the US Army Medical Research Institute of Infectious Diseases (34).

CDC established Ebola Response Teams composed of CDC experts in infection control, clinical care, contact tracing, communications, environmental waste management, and other areas to support state and local health departments and to deploy to any hospital in the United States that has a patient under investigation for Ebola (35). CDC staff arrived at New York City’s Bellevue Hospital before Ebola was confirmed in the patient treated there.

To strengthen protection throughout the United States and to preclude restrictions on travel that could have undermined the response in West Africa and led to surreptitious travel from the region, CDC, together with the US Customs and Border Protection and state and local public health departments, developed a postarrival monitoring program to educate and follow >20,000 travelers arriving in the United States from Guinea, Liberia, and Sierra Leone since October 2014 (36). Travelers are met at the airport and provided with Check and Report Ebola (CARE) kits that include health education materials, a thermometer, and ways to connect with their state or local health department, including a prepaid cell phone. Through mid-May 2015, >1,200 travelers were referred to CDC for additional screening because of illness or, more commonly, to assess possible exposures; 28 persons were referred for medical evaluation. Ebola was not diagnosed in any of these persons (37).

Nearly 500 persons considered to be at “some or high risk” received direct active monitoring that included daily direct observation of symptoms and temperature monitoring by health workers. More than 20,000 travelers classified as “low but not zero risk” received active monitoring, in which they monitored their own temperature and any symptoms and reported daily to the state or local health department until 21 days after their departure from an Ebola-affected country (an effort that has involved >400,000 cumulative contacts with arriving travelers). Health departments facilitated safe transport to a hospital ready to assess travelers for Ebola if the person developed fever or other symptoms of concern.

Before initiation of the active monitoring program, 1 case of Ebola was detected by self-monitoring; rapid detection and isolation prevented further disease transmission. Every jurisdiction now monitors travelers arriving from the highly affected countries and reports to CDC.

The Ebola epidemic in West Africa is unprecedented in size and geographic distribution; it spread in many areas unfamiliar with the disease, including the first large urban outbreaks of Ebola. If the response in West Africa and global assistance had been implemented earlier, faster, and more effectively, far fewer cases and deaths and much less social and economic disruption would have occurred. The epidemic has shown that critical improvements are needed in 2 main areas. First, the ability of every country to quickly identify and respond to a health threat needs to be enhanced. Second, the ability of the global community to rapidly respond to needs in a country overwhelmed by an epidemic must be improved.

For months, the Ebola epidemic spread faster than the international community, including CDC, responded. Critical barriers in the affected countries include limited electronic connectivity (38); insufficient numbers of trained staff; inability to surge rapidly enough to provide needed case detection, education, contact tracing, and isolation services; and poorly functioning national health and public health systems with staff who often were unpaid, untrained, and poorly supervised. Surveillance and data management systems were overwhelmed; solutions are needed to manage, track, and support large outbreaks and public health interventions.

Stronger national and international systems for disease detection and control are needed. Paradoxically, the world is better prepared to find and stop emerging health threats than at any time in history, yet also is at greater risk for rapid spread of infectious diseases, which occur more frequently because of encroachment into forest areas, spread of antimicrobial-resistant organisms, and increasing ease of creation of dangerous pathogens, in the context of an increasingly mobile, interconnected, and urban world. The global community must use these lessons to improve response systems for large-scale emergencies, following the principles of the International Health Regulations, while using core staff and facilities on a daily basis to respond to ongoing health problems.

If the 3 highly affected countries had had effective surveillance and containment systems in place before 2014, the outbreaks might have been detected and stopped promptly (39). There was an unrecognized need for more effective control in urban areas with mobile populations. The use of the incident command system in this complex scenario was critical for organizing focused efforts to stop chains of transmission at the community level and within the health care system. Trust and coordination had to be established with more diverse communities, many of which were in postconflict environments, than in past outbreaks. In all 3 countries, emergency risk communication was a dynamic process, changing as the outbreak evolved, to promote understanding of nuanced messages of risk. Community engagement and understanding of each local community’s beliefs and traditional practices was critical to success of the overall response and particularly important to ensure rapid isolation of infected patients, complete elicitation and monitoring of contacts, and safe burials.

In Uganda, where CDC and others have invested in public health for years, cases of Ebola and Marburg virus disease are now diagnosed promptly, infection control and contact tracing quickly implemented, and outbreaks either stopped rapidly or prevented altogether (40). Similarly, leveraging infrastructure and assets developed through the polio eradication efforts in Nigeria enabled an effective rapid response and demonstrated the value of investing in core public health capacities and training epidemiologists through the country’s FETP program, which is needed in countries around the world. In contrast, before the outbreak, CDC had limited activities and no offices in any of the 3 heavily affected countries. The Global Health Security Agenda, supported by the United States in partnership with other nations and international organizations, seeks to rapidly improve the capacity of countries throughout the world to find, stop, and, wherever possible, prevent the spread of health threats (41,42).

Sustainable response capacity of international entities also needs to be improved. There were initial delays in effective response by WHO country offices and initial resistance of these offices and the African Region of WHO to involve CDC and other organizations (43). WHO has since mounted an effective response supporting the core public health interventions to stop spread of Ebola and is working to become more effective. The Global Outbreak Alert and Response Network is designed to provide a global response (44) but needed more staff with a wider range of skills to be deployed rapidly and for longer periods of time. Organizations that participated in the response needed a broad range of skills, including expertise not only in laboratory and epidemiologic functions but also clinical care, logistics, health communications, information technology, data management, and anthropology, as well as fluency in English, French, and local languages and substantial knowledge of the cultural, social, and religious sensitivities that need to be addressed to engage communities and stop the spread of disease. CDC, along with communities, health care workers, and leaders in the affected nations and the international community, will continue to respond until the Ebola epidemic ends and is committed to strengthening national capacities in West Africa and elsewhere to prevent similar epidemics in the future.