The human immune system is a group of dedicated cells and tissues that fight off infectious agents such as bacteria or viruses. When a virus invades your body, your immune system responds to try to eliminate the virus. This response may include fever, inflammation and the creation of certain proteins, called antibodies, that help fight the infection. The process doesn’t always work, but for many mild viral infections, such as common colds, the immune system is able to contain and mitigate the virus and return your body to health.
Generally speaking, once you have antibodies for a specific pathogen, it’s harder to get sick with that same disease again because those antibodies are able to “recognize” the pathogen and deactivate it when it enters the body. Again, it doesn’t always work this way, but that’s the basic idea of how people can acquire immunity to certain diseases.
Depending on the specific pathogen, these antibodies may stay in your body for months or years, potentially even the rest of your life. This is why it’s very unlikely for you to get chickenpox twice — your body recognizes it if you’re exposed again and can usually fight it off.
When your immune system successfully deploys antibodies in response to a virus it has previously responded to, you probably won’t get sick with that illness again, so you’re considered immune to that specific pathogen. It should be noted, though, that some people who’ve had chickenpox as children develop a related condition called shingles later in life. Shingles occur when the chickenpox virus becomes reactivated in the body, which may occur when you’re overly stressed or otherwise unwell — and the immune system can’t function quite how it should.
This is also the underlying principle behind how most vaccines work — by delivering a dose of either live or inactive viral particles to the body, the immune system ramps up production of the necessary antibodies to fend off a particular illness.
Vaccines are a way of giving your body the immunity it needs to fend off viruses that would cause the flu, measles, polio and other diseases. Those who’ve been inoculated often never even know they’ve been exposed or infected with the virus the vaccine protects against.
Not every virus functions the same way, though, and extensive research into whether the SARS-CoV-2 virus that causes COVID-19 generates enough antibodies to impart a durable immune response is unclear. But there’s plenty of reason to hope that a vaccine can be developed, and, in fact, clinical trials have already started.
