Introduction
Vaccines | What vaccines do | Gaining immunity | Using vaccines | Herd immunity | Diseases | R naught | Vaccine safety | Vaccine effectiveness | Vaccine waning rate
Overview
Vaccines
Vaccines are an important part of fighting illness in humans, livestock, and our pets. The first vaccines were developed in the late 1700s. Now, depending on where they live, people across the globe can use vaccines to protect against severe disease from over 25 different pathogens.
What vaccines do
Vaccines are a way to train our bodies how to fight specific viruses and other pathogens. They introduce our immune systems to parts of viruses, dead viruses, or viruses that are similar to ones we know cause major health problems. When we are exposed to the vaccine, our bodies learn how to quickly recognize the pathogen, and which pathogen-fighting molecules, called antibodies, need to be made to win the fight. That way, if we encounter the real virus later, our bodies can fight it off more quickly, which means the symptoms will be milder or we won't get sick at all.
Gaining immunity
There are only two ways that your body can learn how to fight a disease. It either has to fight the real pathogen and win, or it needs to be trained against that pathogen with a vaccine. Vaccines are the safest way for us to gain immunity against dangerous pathogens.
Using vaccines
But what effect do vaccines have when you look at the numbers? For some diseases, like smallpox and polio, vaccines have nearly wiped the pathogens off the globe. This has saved hundreds of millions of lives. For other diseases, like the seasonal influenza viruses, vaccines help millions of people avoid hospitalization every year.
Herd immunity
When a large portion of a population is vaccinated against a disease, that can help protect the people who are at risk of the disease but are not vaccinated. This community-based protection is called "herd immunity," but it can be very hard to reach a level of protection that works for a specific pathogen. Vaccines are the only ethical way to reach herd immunity. With dangerous diseases that have no vaccines, a huge number of people would have to get sick, and many would have to die to reach herd immunity. Even then, it is likely that the "natural" level of protection would still not be high enough to stop the spread.
Vaccines allow us to save lives by providing protection without severe disease. Reaching herd immunity is especially important for people who cannot be vaccinated because they have weakened immune systems. If most of the rest of the population gets vaccinated, it could potentially save the lives of those vaccinated. But it could also save the lives of people who should not be vaccinated for medical reasons. In addition, vaccines may not work on newborn babies, whose immune systems are not well developed (and who are protected by antibodies from their mothers). Herd immunity can help protect those newborns.
Diseases
COVID-19
COVID-19 is caused by the virus SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2). Many people who are infected don't show symptoms. Because of this, those people have a large impact on the spread of the virus. Those who do show symptoms may have fever or chills, tiredness, body aches, headaches, sore throat, loss of taste and smell, and digestive issues. People with more severe cases may have trouble breathing, chest pain, confusion, and problems staying awake. Though COVID-19 can affect people of any age, older adults and adults with other health problems are at the greatest risk of severe disease. COVID-19 spreads more easily than the flu and can lead to more serious illness in those who catch it. The best ways to fight the spread of the disease is through social distancing (staying more than 6 feet away from people outside of your household members), wearing a mask (some are more effective than others), and getting vaccinated against the disease.
Keep up with new findings on the new coronavirus vaccines on our story page, COVID-19 vaccines.
Influenza
The flu is caused by various strains of the influenza viruses. Common symptoms are fever, body aches, headache, coughing, and a sore throat. Some strains of the flu are much more severe than others. The flu can be fatal and results in about 300,000 to 650,00 deaths per year across the globe. Pandemic strains (like swine flu) can cause more fatalities. Most people who are killed by the virus are in high risk groups, including the very old or young, and those with other existing health problems. Influenza is spread through the air, by direct contact with infectious droplets, or through contact with surfaces covered with the virus. Influenza is a virus that does not just infect humans. Pigs and birds can also carry influenza. As the virus passes between different types of hosts, it can mutate and evolve very quickly. This is why the strain we protect against is different every year, and why a different flu shot is available every year.
Measles
Measles is caused by the measles virus. Measles can cause a rash across the body and makes your immune system work poorly. In healthy people, measles is not usually fatal, but it can cause other issues such as pneumonia and other infections. In rare cases, it can cause blindness and swelling of the brain. Measles is extremely contagious; 90% of people who have close contact with someone with measles may get the disease. It can be passed through contact with the germs or by breathing in air with infectious droplets from an infected person's sneeze, cough, or breath.
Polio
Polio is caused by the poliovirus. In some people the disease only causes flu-like symptoms (fever, headache, sore throat, etc.) but in others, it can infect the central nervous system and cause inflammation of the brain or spinal cord, abnormal growth of limbs, and paralysis. Paralysis can also affect the ability to breathe. Polio can be fatal, and rates depend on how it infects. Poliovirus is not airborne; it is only passed through contact with body fluids or bodily waste.
Simulation values
R naught
R0, or "R naught" is a value used to measure the spread of a disease in a population. That value is equal to the number of people that an infected person is likely to infect. R0 is based on how easily the disease spreads, how much of the population is vaccinated, how dense a population is, and what precautions a population takes against the disease. Wearing masks and distancing from one another can have a huge effect in protecting against specific diseases, especially those that are airborne.
Vaccine safety
All vaccines go through thorough safety tests before they are approved for widespread use. Vaccines that are approved are 99.99% safe. Generally, the only safety issues for approved vaccines are experienced by people with weakened immune systems, or by people who have an allergy to a vaccine ingredient. To learn more about vaccine safety, visit Do Vaccines Scare You?
Vaccine effectiveness
Vaccine effectiveness is a measure of how well a vaccine works. Some vaccines, such as the vaccine for polio, have very high levels of effectiveness, around 90% or more with at least two doses. Others, such as the vaccine for influenza, may be around 30 – 50% effective, depending on the year. Because influenza mutates so much, we have to try to predict what the virus will look like every year to plan far enough in advance to make a vaccine that works well enough to be approved. This prediction doesn't always line up with how the virus mutates, which is why some years it may be more effective than others.
Vaccine waning rate
Vaccines work because our immune systems have memories. They learn how to fight off certain pathogens. However, immune memory does not last forever with some pathogens. Whether you fight off a disease or you are vaccinated for it, after enough time, your body can forget how to fight that pathogen. Tetanus and rabies vaccines are two examples, where you need to get regular boosters (every 10 years and 5 years, respectively) to protect yourself from the pathogen.