The Role of Immunity for Coronavirus

What is a Coronavirus?

A coronavirus can be one of the hundreds of viruses that infect birds and mammals, including humans. The name corona comes from the halo of spikes that extend from the virus cells that can be seen under a microscope. According to the CDC (Centers for Disease Control), coronavirus symptoms are often mild, but some strains may cause serious illnesses.

Coronaviruses usually causes upper respiratory symptoms like a sore throat, runny nose, and cough. Some strains also cause gastrointestinal symptoms like diarrhea. It’s likely that at some point in your life, you were infected with one or more coronaviruses that may have caused a mild illness.

Once you’ve been exposed to a strain of coronavirus, you may develop an immunity to that strain that will keep you from getting it again or having milder symptoms the next time you catch it.

What is a Novel Coronavirus?

The designation as a novel corona virus means that humans have never been exposed to it before. Novel means “new.” COVID-19 is a strain of corona virus that was previously found in animals and is new to humans. Viruses can be transferred from one species to another through farms, markets, bites, or even close contact. If the virus can mutate enough to accept a new host to infect, it will infect a new species. The symptoms one species has may be different from the way the virus affects another species.

Acquired Immunity

Generally, people become immune to a virus by active exposure. For many common diseases, a vaccine provides safe, limited exposure that allows the body to develop antibodies without developing the disease. Unfortunately, there is no vaccine for COVID-19 at this time.

If people are infected with the virus and survive the disease, they may develop antibodies that will protect them from getting the disease again. According to the University of Rochester Medical Center, humans often develop antibodies when exposed, but over time, they can lose the antibodies and can become infected again. Viruses can also mutate, so people’s antibodies don’t recognize a new strain and protect against it.

Because COVID-19 is a novel coronavirus (novel meaning new), humans have not acquired any immunity to it. Anyone who is exposed can become infected. Scientists are working on determining who develops strong antibodies, how long these antibodies last, and the likelihood of the virus mutating into another strain that will bypass any current antibodies. But these tests take time, and because COVID-19 is new, scientists are just beginning to study the effects.

Passive Immunity

If a person develops strong antibodies to a virus, doctors may be able to use their antibodies by giving them directly to an infected person. This is known as passive immunity. While this can help someone fight and recover from a virus, the antibody effect is short-lived. The shared antibodies are only borrowed from the original person, and the infected person doesn’t develop antibodies of their own, meaning they can become infected again.

Herd Immunity

Even with modern vaccines for other diseases, populations are not 100% immune. Some people may be allergic to the vaccine, or too young or sick to receive the vaccine. Herd immunity protects these people from becoming infected.

Viruses need a host to survive. While they can live on surfaces like plastic or metal for a short time, to reproduce, they need a host. If the majority of a population is immune to a virus, the virus can’t find enough hosts and eventually dies out. This is known as herd immunity.

When enough people are vaccinated, a virus can’t find enough hosts. People who don’t have immunity don’t get infected because the virus is no longer active in the population.

Scientists don’t know if enough people will become immune to create herd immunity to COVID-19. They also don’t know how long individual or herd immunity may last. These unknown factors make a novel virus difficult to predict.