Vaccines, usually in the forms of shots or nasal sprays, are used to prevent disease, both viral and bacterial. According to a Health and Human Services website article, Vaccine Types, there are several major types of vaccines. These include live vaccines, which use a weakened (attenuated) form of the live pathogen, and inactivated vaccines, which use dead microbes of disease for vaccination.

 

Another type of vaccine discussed is the mRNA (messenger RNA) vaccine. This is currently being used to prevent the COVID-19 virus. Messenger RNA is found in all living things, but the mRNA in a vaccine contains the code necessary to make a protein or part of a protein produced by a pathogen. The mRNA is then injected into the body, where it is picked up by an immune cell. The immune cell makes the protein and displays it on its cell surface. Antibodies recognize it as foreign, and an immune response is triggered.

 

Also mentioned were subunit vaccines, which include polysaccharide, conjugate, and recombinant vaccine types. These vaccine types all have one thing in common: they elicit an immune response using just pieces of pathogens, germs, instead of the whole pathogen. This article kind of glosses over these vaccine types, and for a somewhat deeper look at how each of these works, you have to turn to other resources. Sometimes subunit vaccines also contain additives, called adjuvants, that enhance the immune response.

 

A subunit vaccine may be made from just part of an immune-triggering protein produced by the pathogen. A subunit vaccine might also be made from a bacteria’s hard, polysaccharide outer covering (polysaccharide vaccines), or the hard capsid (protective covering) of a virus.

 

Conjugate vaccines contain the substances from the hard polysaccharide coats of bacteria linked to a pathogen protein. The conjugation of these two items not only triggers a strong immune response for even very young patients under 18 months, but also allows the body to “remember” the invading germ.

 

In recombinant vaccines, part of the DNA of a pathogen, say from the hepatitis B virus, is inserted into the DNA of another type of organism, such as yeast cells, with the result that yeast cells are “tricked” into quickly and safely producing large amounts of an immune triggering protein of the virus, allowing for the manufacture of this recombinant kind of vaccine.

 

The last of the vaccine types discussed were the toxoid vaccines and viral vector vaccines. Toxoid vaccines trigger an immune response to substances produced by some germs, rather than the germ itself. 

 

Viral vector vaccines use a modified version of a relatively harmless virus to deliver protection from a more deadly virus. As of April 2021, some COVID-19 vaccines were in clinical trials which use viral vectors.

 

As the article explained, there are different pros and cons to the different types of vaccines. For example, live attenuated vaccines deliver a strong, long-lasting immune response; however, there is a slight risk of becoming sick from the disease injected (particularly for those with compromised immune systems), and the vaccine must be kept cool during shipping. Vaccines using a dead germ do not have those risks, but may not deliver a strong or long-lasting effect, and so booster shots may be required over time to maintain immunity. Messenger RNA vaccines deliver a strong response, but must be kept super cold during shipping. This limits the number of sites that can deliver the vaccine, and so on.

 

This is not the end of the story. There are still more types of vaccines under development, such as DNA vaccines, which could be easier and quicker to manufacture; mRNA vaccines that are more stable at somewhat higher temperatures; and vaccines that might be used to treat disease after onset, rather than focusing on prevention.