Editorial note: Since the writing of this article, several COVID-19 vaccines have been developed. You can learn about how they work here and here.

We are currently living through a global pandemic due to a new virus that has completely upended our lives. COVID-19 has shown us very clearly that  a microscopic being can kill many people in a short amount of time and disrupt life as we know it. 

Many individuals who become infected with SARS-CoV-2 and develop COVID-19 have mild symptoms. However, others are not so lucky. Over 100,000 people have died from this disease in the United States and without a treatment or a way to combat this virus, we may be looking at a long year.

If a safe, effective vaccine is developed, we will have the ability to protect a large portion of the population (hopefully, everyone) from COVID-19, alleviating the burden on global healthcare systems and  avoiding losing thousands more to this disease.

As of July 7, 2020, more than 145 vaccine candidates were being evaluated for COVID-19, with 15 in the first phase of human clinical trials. As noted in a commentary published in Nature Reviews: Drug Discovery, the researchers working to develop these vaccines for COVID-19 are taking advantage of novel approaches and new technologies, which may lead to faster development and manufacturing of the amounts needed to treat large populations.

Regardless of the approach, a global herculean effort will be required to ensure any vaccine for COVID-19 is both safe and effective. According to a press release from the National Institutes of Health, “developing COVID-19 vaccines will require unprecedented cooperation from governments, academic institutions, industry, and global philanthropic partners.”

Clinical Trial - VaccineCovid-19, Coronavirus in vial with syringe on white background. Fake label.
As of July 7, 2020, there were more than 145 vaccine candidates for COVID-19

What are vaccines and how do they work?

When we are exposed to a pathogen – a microorganism that causes disease, like a bacterium or virus –  the immune system goes to work to make us better by destroying that pathogen. A pathogenic infection can cause illness, and in some cases, may put us at risk for serious health issues or death. Vaccines protect us by working with the immune system to develop defenses so that if we are exposed to certain pathogens, we are prepared to fight them.

Today, vaccines are our best weapon against the viruses or bacteria that cause measles, mumps, tetanus, influenza, whooping cough, human papillomavirus (HPV), hepatitis A and B, chickenpox, meningitis, and diphtheria, among others. They do so without us ever having to be sick. This is because vaccines expose the immune system to a modified version of a pathogen. When you are exposed to the real thing, your immune system reacts quickly to deal with the infection through immunological memory, where your body remembers what to do to clear the infection because the vaccine taught it how.

There are two main cell types that carry out this quick response: B cells and T cells. The presence of a foreign bacteria or virus activates B cells to produce antibodies – molecules that circulate in the bloodstream and bind to a specific part of the pathogen, either neutralizing it or tagging it to be destroyed by other immune cells.

These are the most common vaccine types, some of which are currently in development for COVID-19:

Live attenuated vaccines contain the pathogen itself, but a weakened version of it. Since this version of the pathogen is likely to be most similar to the natural pathogen, live attenuated vaccines tend to induce stronger and longer-lasting immunity. Because of this, they cannot be administered to those with weakened immune systems. Examples of live attenuated vaccines include those for measles, mumps, and chicken pox.

Inactivated vaccines contain a non-active form of the pathogen, created by treating the live pathogen with chemicals, heat, or radiation. Since the pathogen is inactivated or killed by these procedures, the immune response to these types of vaccines tends to be weaker; this is why you may have to go back for a “booster” to reinforce the immunological memory that was initially formed. 

Toxoid vaccines were developed to defend against certain bacteria that release toxins during infection. Toxoids are weakened bacterial toxins, like those from the bacteria that cause tetanus or diphtheria, and are included in vaccines to train the adaptive immune system to destroy the natural toxin when encountered.

Subunit vaccines, like the one for whooping cough, contain only a part of the pathogen they are designed to fight – the part that will induce an immune response. 

Finally, conjugate vaccines are a specialized type of vaccine that helps the immune system recognize the coating of certain bacteria, made up of sugars called polysaccharides. These vaccines contain the bacterial antigen attached to polysaccharides, which trains the immune system to induce immunity and identify bacterial pathogens with a polysaccharide coating.

Until a vaccine becomes available, scientists will continue to learn all that they can about this novel virus and, hopefully, in addition to a new vaccine, new effective treatment options will emerge.