Pandemics and Infectious Diseases


A pandemic is the sustained transmission of an infectious disease across a wide area of one country or across international borders.

Pandemics may be either naturally occurring (such as avian flu) or the result of human intervention through genetic engineering or biological warfare. The World Health Organization (WHO) identifies six phases of influenza pandemics:

  • Phase 1: No animal influenza virus circulating among animals have been reported to cause infection in humans.
  • Phase 2: An animal influenza virus circulating in domesticated or wild animals is known to have caused infection in humans and is therefore considered a specific potential pandemic threat.
  • Phase 3: An animal or novel human-animal influenza virus has caused sporadic cases or small clusters of disease in people but has not resulted in sustained human-to-human transmission.
  • Phase 4 (Outbreak): Sustained human-to-human transmission of an animal or novel human-animal influenza has resulted in ongoing community-level outbreaks.
  • Phase 5 (Epidemic): The same identified virus as in Phase 4 has caused sustained community-level outbreaks in two or more countries.
  • Phase 6 (Pandemic): The same virus as in Phase 5 has caused sustained community-level outbreaks in at least one other country outside of the same geographic region as Phase 5.

While the influenza virus is the most likely to cause more widespread outbreaks, the risk is not limited solely to influenza or even to viruses. The bubonic plague and anthrax are infectious diseases that are caused by bacteria which could also result in a pandemic.

WHO is the global body responsible for monitoring, tracking, responding to and mitigating infectious disease outbreaks around the world. Along with national health bodies such as the U.S. Centers for Disease Control and Prevention (CDC), WHO has established a series of International Health Regulations (IHR) to help reduce the possibility of a global pandemic. The IHR provide a framework upon which countries can build legislation and policies to ensure the safety of their citizens.

In the U.S., the CDC is responsible for monitoring, tracking, responding to and mitigating infectious disease outbreaks, along with local and state health authorities. Working cooperatively with other federal agencies such as Customs and Border Protection, the CDC ensures that outbreaks of infectious disease in the U.S. are handled quickly and appropriately before they can become epidemics or pandemics.

Most viral infectious diseases including polio, measles and mumps can be easily prevented through routine vaccinations. However, anti-science and anti-vaccination sentiments, coupled with the financial cost of healthcare in many countries, mean that some people are not receiving routine vaccinations. This has resulted in recent outbreaks of infectious diseases once considered eradicated, such as measles and polio.

WHO data about estimated vaccine coverage in nations show that some “still-developing” countries have better vaccine coverage than some “developed” countries. In 2018, only 87 percent of Canadian babies had received the first dose of the Diphtheria, Tetanus and Pertussis vaccine compared with over 99 percent of babies in Afghanistan. And, a 2019 article in The Lancet about vaccine coverage in Africa states: “Future increases in coverage are anticipated to return large health benefits, but coverage rates in many countries across the continent are far from national targets, with many rates stagnating or falling.”

Most bacterial infections, including anthrax and the bubonic plague, are easily treatable with good outcomes if they are quickly diagnosed and rapidly treated. Unfortunately, the cost of treatment in the U.S. and other countries without a national healthcare program often prevents people from seeking out treatment or causes significant financial hardship (up to and including bankruptcy).

Key Facts

  • The next pandemic strain of influenza is expected to be a variant of an animal influenza. Viruses of all types are continually changing and adapting based on their interactions with the world around them. As animal influenza strains come into contact with humans, they adapt to become infectious to humans. Current animal influenzavariants that have been identified as causing human infections include H5N1, H5N6 and H7N9 – all of which are capable of animal-to-human transmission but have not achieved sustained human-to-human transmission.
  • Pandemic strains of influenza are different from seasonal strains of influenza. Humans have the ability to build up resistance to many infectious diseases either through exposure or vaccinations. Seasonal influenzas are those virus types that regularly circulate through the human population – currently Influenza A types H1N1 and H3N2, as well as Influenza B. Pandemic strains do not normally circulate through the human population so there is little to no immunity through either exposure or vaccinations.
  • Infectious diseases can rapidly spread through global travel, especially by air. Affordable and plentiful air travel means a person with an infectious disease can travel to countries far away from where they contracted the disease, spreading it along the way. The person may not even be aware that they have an infectious disease because they have not started showing symptoms. They may spread the disease to others on the plane, who may in turn continue spreading it through their continued travel or to people around them.
  • New research is changing previously fatal diseases into both preventable and treatable diseases. Recent years have seen multiple outbreaks of Ebola hemorrhagic fever (Ebola) that have killed thousands of people in Africa. Since it was first detected in humans 40 years ago, Ebola has been almost certainly fatal to those who contract it. Research and development in recent years have resulted in effective vaccines and effective treatments that have reduced the fatality rate to under ten percent in some cases.
  • Proper Water, Sanitation and Hygiene (WASH) programs are essential to preventing infectious diseases and reducing the possibility of transmission. One of the most effective ways to reduce or prevent transmission of infectious diseases continues to be adequate handwashing with soap and water. People who do not have regular access to adequate WASH systems are often subject to outbreaks of easily preventable diseases.
  • Displaced people and those in emergency and interim shelter are at increased risk for infectious diseases.Many people who are displaced do not have access to disease prevention tools such as vaccines and adequate WASH systems. Some may have already contracted an infectious disease during or prior to their displacement. Crowded conditions, along with inadequate WASH and medical systems in emergency and interim shelters can contribute to increased disease transmission within the sheltered or displaced population. Local, state and territorial public health units in the U.S. and abroad are often active in offering vaccines or treating illnesses. Many health-care based nongovernmental organizations (NGOs) provide support after a disaster or in a humanitarian emergency.
  • Vaccines save lives. According to UNICEF, “Vaccines protect children against disease and death, saving up to three million lives every year – more than five lives saved every minute of every day. … 1.5 million deaths could be avoided if global immunization coverage improves.”

How to Help

  • Support programs that provide immunizations to low-income people around the world. Most infectious diseases can be prevented by routine vaccination schedules for children and adults. While some people have legitimate reasons to not receive a vaccination (as identified by a medical professional), it is important that as many people as possible are vaccinated in order to prevent the transmission of infectious diseases and protect those who cannot receive vaccinations. UNICEF often offers mass vaccine clinics after disasters as it is an efficient way to reach a large population base. Some U.S. communities offer tetanus vaccines to people affected by a disaster.
  • Support healthcare organizations who make vaccinations available at low- or no-cost. In the United States, along with many still-developing countries, people must often pay for vaccines out of pocket. These can be expensive, with single doses ranging in cost from $9.50 to $228.
  • Fund research into new vaccines and treatments for infectious diseases. As evidenced by the advances in prevention and treatment for Ebola, research that provides new insights into vaccination and treatment for infectious diseases can radically change the risk from an infectious disease.
  • Support WASH (Water, Sanitation and Hygiene) programs, particularly in still-developing countries or places where there are large numbers of displaced people. In addition to supporting WASH programs, support for research and development of new and lower-cost WASH technologies can also have a significant impact on infectious disease transmission.
  • Provide support for health organizations working in places with large numbers of displaced people, ongoing conflict or low-income residents. The Center for Disaster Philanthropy works with donors and recipients to ensure that philanthropic funds are directed to the places where they will have the most impact.

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(Photo: Medics in full safety gear at the entrance to an isolation unit. Source: Simon Davis/DFID)