The current worldwide outbreak of COVID-19 has left many people with concerns about the spread of this new disease. Among those concerns is one important underlying question: What exactly is a pandemic?

The spread of the novel coronavirus, SARS-CoV-2, was officially defined as a pandemic by the World Health Organization (WHO) on March 11, 2020, due to its sudden emergence and expansion around the world.

In this article, we’ll explore what defines a pandemic, how to prepare for a pandemic, and how many pandemics have affected us in recent history.

According to the WHO, a pandemic is defined as the “worldwide spread of a new disease.”

When a new disease first emerges, most of us lack the natural immunity to fight it off. This can cause a sudden, sometimes rapid, spread of the disease between people, across communities, and around the world. Without a natural immunity to fight off an illness, many people can become sick as it spreads.

The WHO is responsible for announcing the emergence of a new pandemic based on how the spread of the disease fits into the following 6 phases:

  • Phase 1. Viruses circulating among animal populations haven’t been shown to transmit to human beings. They’re not considered a threat and there’s little risk of a pandemic.
  • Phase 2. A new animal virus circulating among animal populations has been shown to transmit to human beings. This new virus is considered a threat and signals the potential risk of a pandemic.
  • Phase 3. The animal virus has caused disease in a small cluster of human beings through animal to human transmission. However, human to human transmission is too low to cause community outbreaks. This means that the virus places humans at risk but is unlikely to cause a pandemic.
  • Phase 4. There has been human-to-human transmission of the new virus in considerable enough numbers to lead to community outbreaks. This kind of transmission among humans signals a high risk of a pandemic developing.
  • Phase 5. There has been transmission of the new virus in at least two countries within the WHO region. Even though only two countries have been affected by the new virus at this point, a global pandemic is inevitable.
  • Phase 6. There has been transmission of the new virus in at least one additional country within the WHO region. This is known as the pandemic phase and signals that a global pandemic is currently occurring.

As you can see above, pandemics aren’t necessarily defined by their growth rate but rather by the spread of the disease. However, understanding the growth rate of a pandemic can still help health officials prepare for an outbreak.

Many disease outbreaks follow a growth or spread pattern described as exponential growth. This means they spread at a rapid rate over a specific period of time — days, weeks, or months.

Think of driving a car and pressing on the gas pedal. The farther you travel, the faster you go — that’s exponential growth. Many initial disease outbreaks, like the 1918 influenza pandemic, seem to follow this growth pattern.

Some diseases also spread sub-exponentially, which is at a slower rate. This is like a car that maintains speed going forward — it doesn’t increase in speed across the distance it travels.

For example, one research study found that the 2014 Ebola epidemic seemed to follow a much slower disease progression at the local level in some countries even though it spread faster, or exponentially, in others.

When public health officials know how quickly a disease is spreading, it can help them determine how quickly we need to move to help slow that spread.

Pandemic and epidemic are related terms used to define the spread of a disease:

  • An epidemic is the spread of a disease in a community or region over a specific amount of time. Epidemics can vary based on the location of the disease, how much of the population has been exposed, and more.
  • A pandemic is a type of epidemic that has spread to at least three countries within the WHO region.

A pandemic can be an uncertain time for many people around the world. However, pandemic prevention tips can help you prepare for the worldwide spread of a disease:

Pay attention to news reports from health agencies

News updates from the WHO and Centers for Disease Control and Prevention (CDC) can provide information on the spread of the disease, including how to protect yourself and your family during the outbreak.

Local news can also keep you updated on new legislation that is being enforced during the pandemic.

Keep your house stocked with a 2-week supply of food and essentials

Lockdowns and quarantines may be enforced during a pandemic to slow or stop the spread of the disease. If possible, keep your kitchen stocked with enough food and essentials for about a 2-week period. Remember, there’s no need to stockpile or hoard more than you can use over 2 weeks.

Fill your prescriptions ahead of time

It can help to have medications filled ahead of time in the case that pharmacies and hospitals become overwhelmed. Keeping over-the-counter drugs can also help ease any symptoms you might experience if you contract the disease and need to self-quarantine.

Make a plan of action in the event of illness

Even if you follow all the protocols recommended during a pandemic, there’s still a chance you could become sick. Talk to family and friends about what would happen if you become ill, including who will take care of you and what will happen if you need to be admitted to the hospital.

We have experienced seven notable epidemics like COVID-19 since 1918. Some of these epidemics have been classified as pandemics, and all of them have had a serious effect on the human population in some way.

Spanish Flu (H1N1 virus): 1918–1920

The 1918 influenza pandemic took the lives of anywhere from 50 to 100 million people around the world.

The so-called “Spanish Flu” was caused by an H1N1 virus that spread from birds to humans. People ages 5 and younger, 20 to 40, and 65 and older all experienced high mortality rates.

Overcrowding in treatment areas, poor sanitation practices, and nutritional deficiencies are thought to have contributed to the high death rate.

Asian Flu (H2N2 virus): 1957–1958

The 1957 influenza pandemic took the lives of roughly 1.1 million people worldwide.

The “Asian Flu” was caused by an H2N2 virus that also spread from birds to humans. This strain of the flu affected people primarily between the ages of 5 and 39, with the majority of cases occurring in younger children and teenagers.

Hong Kong Flu (H3N2 virus): 1968–1969

In 1968, the H3N2 virus, sometimes called Hong Kong Flu, was another influenza pandemic that took the lives of around 1 million people around the world.

This flu was caused by an H3N2 virus that mutated from the H2N2 virus from 1957. Unlike previous flu pandemics, this pandemic primarily affected older people, who had the highest mortality rate of the outbreak.

SARS-CoV: 2002–2003

The 2002 SARS coronavirus outbreak was a viral pneumonia epidemic that took the lives of over 770 people worldwide.

The SARS outbreak was caused by a new coronavirus with an unknown transmission source. Most of the infections during the outbreak started in China but eventually spread to Hong Kong and other countries around the world.

Swine Flu (H1N1pdm09 virus): 2009

The 2009 Swine Flu outbreak was the next influenza pandemic that caused the deaths of somewhere between 151,700 and 575,400 people around the world.

The Swine Flu was caused by another H1N1 virus variant which originated from pigs and eventually spread through human-to-human contact.

It was discovered that a portion of people aged 60 and older already had antibodies against this virus from previous flu outbreaks. This led to a higher percentage of infection in children and young adults.

MERS-CoV: 2012–2013

The 2012 MERS coronavirus caused a disease characterized by severe respiratory illness that had a 34 percent mortality rate and took the lives of 858 people, primarily in the Arabian Peninsula.

The MERS outbreak was caused by a coronavirus that spread from an unknown animal source to humans. The outbreak originated in Saudi Arabia and was contained primarily to the Arabian Peninsula.

The MERS outbreak had a much higher mortality rate than the previous coronavirus outbreak.

Ebola: 2014–2016

The 2014 Ebola outbreak involved a hemorrhagic fever epidemic that took the lives of 11,300 people, primarily in West Africa.

The Ebola outbreak was caused by an Ebola virus that is thought to have been initially transmitted from bats to humans. Although the outbreak started in West Africa, it spread to eight countries in total.

COVID-19 (SARS-CoV-2): 2019–ongoing

The 2019 COVID-19 outbreak is a viral pandemic that’s currently ongoing. This is a new illness caused by a previously unknown coronavirus, SARS-CoV-2. The infection rate, mortality rate, and other statistics are still developing.

Preparing for a pandemic is a community effort that we can all take part in to lessen the impact of the illness on our communities and around the world.

You can find live updates on the current COVID-19 pandemic here. Visit our coronavirus hub for more information about symptoms, treatment, and how to prepare.

When a new disease emerges, there is the possibility of a pandemic, which is worldwide spread of the disease. There have been multiple pandemic and epidemic outbreaks in recent history, including the 1918 influenza pandemic, the 2003 SARS-CoV outbreak, and most recently, the COVID-19 pandemic.

There are things we can all do to prepare for a possible pandemic outbreak, and it’s important that we all follow the appropriate steps to slow or stop the spread of the new disease.

For more information on how you can do your part to slow the spread of COVID-19, click here for the current guidelines.