There are two ways to acquire immunity to an infectious disease: get sick and survive it or get vaccinated. Interest in vaccines has risen in response to the coronavirus pandemic. Understanding how vaccines are made facilitates conversations between doctors and patients about vaccine options, benefits, and possible risks.
Vaccines work by teaching the body to recognize a pathogen and to react by generating antibodies to fight the infection, mimicking the natural immune system response when a person comes down with a sickness. Vaccines sometimes need time to take effect, and immunity doesn’t always last a lifetime for some diseases, so booster shots or annual vaccines are necessary. It’s possible to get sick after being vaccinated, but the vaccination will reduce the severity of the illness.
Vaccines fall into five general groups:
Attenuated: these are live pathogens that have been weakened so they no longer cause disease, but they still stimulate the immune response that creates antibodies against the illness. They can’t be given to people with weakened immune systems. This type is becoming rarer, as newer vaccines tend to fall into one of the other four groups.
Inactivated: these vaccines contain viruses killed with chemicals, heat, or radiation so they can’t cause disease, but they still stimulate the production of antibodies that “remember” the virus and will battle it if a live version enters the vaccinated person’s system. Sometimes multiple doses are necessary to achieve the desired immunity.
Subunit: pieces of the pathogen, usually the outer layer, without the other parts that cause disease, make up subunit vaccines. These vaccines trigger an immune response because the outer layer is what the immune system reacts to first when the virus enters the system.
Conjugate: some bacterial pathogens fool the immune system with coatings that resemble sugars. Harmless proteins are attached or “conjugated” to cells with those coatings to enable the immune system to recognize an invader and send out cells to attack it.
Toxoid: inactivated or killed toxins become “toxoids.” The killed toxins won’t cause disease but do create an immune response.
Leaning how vaccines are made may send your mind back to your college biology class; to create a vaccine, the virus or bacteria is grown in live host cells from animals, yeast, or in a nutrient broth within a bioreactor. Over several generations, the pathogens change to become harmless to humans, or they become acclimated to conditions (such as low temperatures) that cause them to lose the ability to reproduce within the human body. Sometimes, vaccine producers inject only the gene responsible for the part of the germ that induces an immune response. The result won’t cause the disease, but it will trigger the production of antibodies.
After enough of the pathogen grows, it is filtered out of the host cells and treated as necessary (killed, conjugated, etc.). Additives that enhance the immune response, stabilizers in case the vaccine is exposed to extreme conditions, and preservatives to prevent the growth of microbes may be introduced. Vaccines must be proven safe and effective to gain FDA approval for use.