A pandemic happens when a disease spreads across several countries at the same time. Pandemics can be challenging to deal with because doctors cannot treat all the sick people at once.
How do Diseases Spread?
Diseases that affect the respiratory tract can spread through water droplets. When you breathe, talk, or chew with your mouth open, you are constantly releasing millions of tiny water droplets. When you cough or sneeze, you shoot these tiny droplets into the air.
Some of the droplets are heavy and drop to the ground quickly. Other droplets are very small particles that can hang in the air for a long time. The measles virus, for example, can last in the air for 8 hours. That makes measles very contagious!
Scientists describe how fast a disease spreads by determining the average number of people an infected person will pass the virus to. They call this average number “R0”. (This is pronounced “are not” – as in, “You R0 a hippopotamus.”)
This is simply a way of explaining how many people are likely to be infected by one sick person. With an R0 of 2, each infected person will spread the disease to two other people. If it takes one week to transmit the illness from one person, in 10 weeks, about 500 people will be infected with an R0 of 2.
In 20 weeks, the number of people infected is over 500,000.
In less than six months, a disease with an R0 of 2 can grow from just one person to infect the entire human race, if nothing is done to stop it.
To end the spread of an illness, the R0 needs to be less than 1. When each infected person gives it to less than one other person, the virus will eventually die out.
Immunity to Disease
When your body gets a disease for the first time, it isn’t prepared. The disease spreads through your body, and your immune system must work hard to fight it off. However, your immune system figures out how to recognize the disease, so it will be ready the next time.
If you get exposed to a virus a second time, your immune system will be ready. It can recognize the invader right away and fight it off. Your body produces antibodies to catch the viruses or bacteria, and white blood cells come in to gobble them up. For instance, you can only get chickenpox once. The chickenpox vaccine teaches your body what to look for, so a vaccine can also make you immune, without having to actually get chickenpox.
SARS-CoV-2 the virus that causes COVID-19, is completely new to the human population. Unlike the flu or the common cold, no one is immune. So, the virus can easily transfer to every person it encounters. If the virus sweeps through the human population all at once, many people could die because there simply aren’t enough doctors to help everyone!
That’s why it’s important to wear a mask, wash your hands often, and avoid large groups of people. This will give us time to develop a vaccine and eventually beat the virus. Plus, by slowing the spread of the virus, we can ensure that everyone can have a doctor when they get sick.
The difference between epidemic, pandemic, and endemic diseases
Pandemics happen when a disease spreads across the entire world. Fortunately, they don’t happen too often. Before COVID-19 in 2020, the last major pandemic was a flu pandemic in 1918.
An epidemic happens when many people in a single region get the same illness. COVID-19 started out as an epidemic in Wuhan, China. When it spread to countries around the world, it became a pandemic.
Endemic diseases are illness that appears in a population at a steady rate and never go away. An illness may start as an epidemic, flare up into a pandemic, and then hang around as an endemic disease, continuing to make a few people sick every year.
Written by Laura McCamy
Edited by Gabriel Buckley, MS Professional Natural Sciences
Illustrated by Meimo Siwapon