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Response to epidemics in humanitarian crises

  • Page updated onMarch 16, 2025
Response to epidemics
Photo: Bruno Abarca

In humanitarian contexts not only does the risk of infections increase, but also the response to epidemics becomes more difficult. It is common for the scarce health personnel to be overwhelmed and the supply of medicines to be cut off. In addition, essential health services such as vaccination, and even essential public health functions are disrupted.

If routine epidemiological surveillance is not guaranteed, an alternative is necessary. In such cases, it is recommended to implement an Early Warning Alert and Response System (EWAR) or strengthen it if it already exists. This will identify signals, manage alerts and guide outbreak control measures.

Epidemiological surveillance to detect signals and manage alerts

Detection of potential public health events is key to epidemic response

Epidemiological surveillance can be performed from a functional health information system, or as a component of an emergency EWAR system. This system, ideally, should be integrated into the public health system. In addition, it should be led by the national public health authorities, with technical support from WHO and other actors.

In any case, existing epidemiological surveillance should be able to detect signals. Signals are possible public health events, which are not yet verified. They occur when the number of cases of some diseases exceeds alert thresholds. In most cases, it is not possible to monitor all possible diseases. Instead, a set of 8-12 diseases or health conditions considered as priority is selected. To enable signals to be detected, information on these priority diseases will be collected in regular periodic reports. Signals may also be produced when information about potential public health events arrives by any other route. This includes citizen warnings or notifications received through media.

Signal detection is only the first step on the road to a possible response to an epidemic. The second step is alert management. Managing alerts requires verifying signals, analyzing risks, and finally deciding whether to respond to an epidemic.

Once a signal has been detected, its validity must be proactively assessed

The process of signal verification is fundamental in the response to epidemics. It is what allows "filtering out" false signals. These can be produced by calculation errors, data artifacts, warnings based on false rumors, or repeated warnings, among other causes.

For example, a signal may come in the form of a phone call from a nurse at a remote health post. In this hypothetical call, she reports that this morning several users of the post told her that a neighbor's house had a child with a rare paralysis. Hearing that the child could not move his limbs on one side, the nurse thought of a possible case of polio. 

Once the signal is detected, verification must be done very quickly, within 24 hours. Generally, a signal can be verified if consultation with the source that reported the signal confirms that the source is reliable. This requires that the clinical case description is reliable and that the epidemiology appears plausible. In other cases, in addition, a signal may be consistent with other signals received in the same period, for example. A verified signal constitutes an event: the manifestation of a disease or a potentially pathogenic event.

It is necessary to determine the risk that each public health event poses to human health

The next step, with each event, is to complete an analysis to determine the risk posed to human health. This is sometimes done locally. However, in other cases it may require sample collections for laboratory analysis. It may even require field visits by specialized rapid response teams. The advantage of having these teams, moreover, is that they can quickly initiate an in-depth investigation of the public health event, if necessary.

The risk analysis includes:

  • A hazard assessment. This analysis addresses aspects such as the number of cases or whether they are laboratory confirmed or not. It also takes into account whether it is a pathology with a high risk of mortality or rapid transmission.
  • An exposure assessment. This involves estimating the number of individuals who may have already been exposed to the event. The number that could be exposed in the following days and weeks is also estimated.
  • A contextual assessment. This includes aspects such as vaccination coverage, access to water and sanitation or malnutrition rates. It also addresses the availability of health services or the current capacity of the epidemiological surveillance system. This analysis also helps to contextualize the public health event, if it may be affected by conflict or displacement, for example.

The outcome of this risk analysis may determine that the event poses a public health threat. This may be due to its potential impact on human health, its high risk of transmission, or insufficient local capacity to respond. In such cases it is referred to as an alert, indicating that a response is needed.

Responding to epidemics: investigation, communication and control measures

Response to epidemics is the set of public health actions that are implemented following the risk analysis of an alert. The response is not only the implementation of control measures. Before that it may include an in-depth investigation of the epidemic outbreak or the search (active or passive) for cases. It also encompasses monitoring the progress of the outbreak and public communication of the epidemic and its risks.

In-depth research makes it possible to characterize in detail the alert

The in-depth investigation of the epidemic outbreak is sometimes a continuous process starting from the verification of the first signal and risk analysis. Now that there is already an alert, a great deal of work is required to characterize the pathogen and the population at risk. This research will also help to determine the control measures that will be necessary in the response to the epidemic. Therefore, it is important that the investigation be led by an expert in epidemiology.

The success of an investigation also requires that the team includes health agents or community leaders. These individuals usually have a thorough knowledge of the local context and population. It is also essential to have the means to collect samples, send them to designated laboratories and have them analyzed there. The laboratory analysis sometimes also includes genomic or antibiotic resistance tests. Throughout this process, which can take several days, some control measures may already need to be determined, despite the uncertainty.

A case-finding strategy may be necessary

The outbreak investigation, among other things, also allows an agreed definition of "case" to be established. This will be key for the epidemiological surveillance system to be able to proceed with a case search. Case-finding strategies depend on the context, the pathogen, or even the evolution of the outbreak.

This search can be passive. It is done by asking the community and health personnel to report all suspected cases that come to their attention. At the same time, just in case, they should take protective measures.

An active search can also be employed. This is accomplished with the support of community and community health workers. These volunteers should visit all families believed to have been exposed to the outbreak. They should also follow up on any rumors they hear. In this way they will identify as soon as possible possible cases that would otherwise never be detected in health units.

Monitoring the progress of the epidemic allows to know the attack and case fatality rate

Thanks to the case search, the surveillance system will also be able to produce and periodically update descriptive analyses of the outbreak and its evolution. These analyses make it possible to show how the number of cases evolves along an epidemic curve. They also provide information about the most affected areas or the population groups most at risk, for example.

In addition, monitoring makes it possible to calculate indicators that, during an epidemic, are essential. One of them is the attack rate. It consists of the proportion of new cases in a population over a period. It also helps to calculate the case fatality rate. This is the proportion of cases that die due to a specific condition. All these data can inform key actions to intensify surveillance or concentrate control measures in an area. Moreover, with this information it can be determined whether a response is relevant. If the attack rate is high, it may be necessary to prioritize vaccination, while if the case fatality rate is higher than expected, the quality of medical care may need to be strengthened.

Public communication of information about the epidemic must be done with great care

In epidemic response, it may be necessary to develop a comprehensive risk communication and community mobilization strategy. Messages should include information on the nature of the epidemic, such as the pathogen, the groups at risk, or the localities affected. But that is not all. It is also necessary to communicate the recommended measures to reduce the risk of contagion or in case of suspicion of exposure or infection and the available resources.

In any case, messages, by themselves, are never enough. The importance of understanding how communities react to epidemics should never be minimized. It is not easy to deal with some people's fear of contagion, others' low perception of risk or the circulation of rumors and misinformation. Sometimes there is also stigma towards patients, exposed persons or healthcare personnel, or fear of this stigma. It is also important to document and understand possible clashes between recommended control measures and social or religious norms, or mistrust of authorities with little transparency and accountability.

In addition, an adequate risk communication and community mobilization strategy must go hand in hand with a two-way dialogue. This allows the community to participate in the analysis of the situation and the identification of control measures. Moreover, their active participation in the implementation of measures and their monitoring can be a success factor. An example of the risk that exists in epidemics in relation to the way in which the community is connected during the response can be seen in the COVID-19 pandemic. This international public health emergency has had a global impact on the distrust of all types of vaccines and the resurgence of infections.

Responding to epidemics requires control measures adapted to the pathogens and contexts

Possible control measures, depending on the pathogen and the context include:

  • The reinforcement of health services, both preventive and curative, with a strong emphasis on ensuring accessible primary care.
  • Promote the adoption of infection prevention and control measures in healthcare centers. To this end, the availability of personal protective equipment should be ensured. The application of universal precautions should also be promoted and supervised.
  • The intersectoral collaboration to ensure water hygiene, animal health or reduction of the risk of further zoonotic transmission, for example.
  • Measures aimed at reducing contact and social interactions among the population at risk.
  • Isolation measures for persons with confirmed infection (for example in the COVID-19 pandemic).
  • The use of vaccines, if available and their use is considered relevant and feasible. They may be important, for example, in epidemics of COVID-19, cholera, measles, Ebola, meningitis, or yellow fever.
  • Chemoprophylaxis measures (e.g. in pregnant women at high risk of exposure to malaria).
  • Adoption of safe (and dignified) funeral practices, in cases where there is a risk of transmission through contact with the corpse, as in the case of ebola.

All these steps and measures may be impossible without access, preparation and coordination

Each and every one of these measures can be a tremendous challenge in the midst of conflict or in displaced populations. They can also be so if the epidemic follows an emergency that has deteriorated living conditions, damaged infrastructure and disrupted access to essential services.

There are a thousand other factors that can make managing an epidemiological alert an almost impossible task in a complex humanitarian crisis. For example, initiating a vaccination campaign against an outbreak may be unfeasible or ineffective in outbreaks that are detected late. This is especially worrisome if transmission and contagion is already widespread in populations weakened by forced displacement. An example of this was the cholera among Rwandan refugees in 1994. In addition to the above, building trust towards humanitarian actors in the population can be difficult in highly politicized contexts. Similarly, the entry of medicines, vaccines or medical personnel may be limited by border closures or restrictions on access, among many other possible examples.

Finally, adequate preparedness of health systems prior to epidemics is also essential for an adequate response to epidemics. Adequate coordination of public health actors during epidemics is also important. This may require urgently establishing new mechanisms adapted to the crisis, beyond the usual humanitarian coordination mechanisms.

Infectious diseases

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