COVID-19 Vaccines

How do they work and what are the different types?

How do COVID-19 vaccines work?

Vaccines protect against illness caused by a virus/bacterium (antigen). They trigger the body’s natural immune response by allowing the body to recognize the antigen and develop antibodies against it. Antibodies are responsible for fighting off and destroying invading agents.

An altered form of the antigen is the vaccine’s active ingredient which allows for the development of immunity without causing actual sickness or an infection. The way in which the antigen is altered depends on the type of vaccine.

In addition, vaccines contain adjuvants. Adjuvants are additives that help increase the vaccine’s immunity. One of the most used adjuvants is insoluble aluminum salts. The insoluble aluminum salts stimulate a fast and broad immune response, which in turn, initiates a more adaptive and specified immune response for the desired antigen.

Vaccines also contain stabilizers and preservatives, which help maintain quality during production and storage. Gelatin is a popular stabilizer and allergen. Sometimes vaccines can cause allergic reactions because of the stabilizers or preservatives they contain. If you have a known allergy, talk to your healthcare provider before receiving a vaccine.

Vaccines can cause short-term side effects; common ones for

Four main types of COVID-19 vaccines

Inactivated (Whole Virus) Vaccines

These vaccines use killed forms of the antigen.

Protein Subunit Vaccines

These vaccines use only a specific protein from the antigen that best stimulates an immune response. COVID-19 vaccines use the virus’s spike protein.

Viral Vector Vaccines

With these vaccines, the genetic material of the antigen is injected into a harmless virus that is different from the targeted antigen. The harmless virus (vector) is a transport mechanism that provides human cells with the genetic instructions to produce parts of the antigen such as spike proteins. The adenovirus, also known as the common cold, is a frequently used vector in COVID-19 vector vaccines.

Nucleic Acid Vaccines

These vaccines contain viral genetic material (DNA/RNA) that cause human cells to produce the antigen or part of it. These COVID-19 vaccines use viral mRNA to code for the virus’s spike proteins.

Vaccine immunity vs. natural immunity

A COVID-19 infection can have serious, and sometimes fatal, consequences. COVID-19 can cause long-lasting effects such as organ damage or post-COVID-19 syndrome. Vaccines help to prevent or lessen a COVID-19 infection and its associated symptoms.

The only way to gain natural immunity is to have been infected with the virus, while vaccine immunity is gained without infection and without the resulting complications. The strength of natural immunity and vaccine immunity are roughly equal with about 6 months of protection against reinfection. Both types of immunity decrease over time. Vaccine booster shots help keep immunity high. The reinfection rate of someone with natural immunity is roughly double that of someone who has vaccine induced immunity. Even if you have already had COVID-19 and have developed natural immunity, it is recommended that you still get vaccinated as this greatly increases your immune protection and lowers your chances of reinfection. In fact, the combination of natural and vaccine immunity offers the highest level of protection against COVID-19.

The goal with COVID-19 mass vaccination is to achieve herd immunity. Herd immunity occurs when enough people have been vaccinated and have developed immunity to a disease so that it no longer is able to spread easily through a community, and in turn, it declines or disappears over time. This decrease in prevalence is how heard immunity protects those who are unable to get vaccinated. Heard immunity achieved through mass vaccination has led to the eradication of many diseases such as smallpox, polio, and rubella to name a few.

References

• Danielsson R, Eriksson H. Aluminium adjuvants in vaccines - A way to modulate the immune response. Semin Cell Dev Biol [Internet]. 2021 Jul [cited 2022 Jul 19];115:3-9. DOI: 10.1016/j.semcdb.2020.12.008.
• Marrack P, McKee AS, Munks MW. Towards an understanding of the adjuvant action of aluminium. Nat Rev Immunol [Internet]. 2009 Apr [cited 2022 Jul 19];9(4):287-93. DOI: 10.1038/nri2510.
• Centers for Disease Control and Prevention (CDC). What’s in Vaccines? [Internet]. Atlanta, GA: U.S. Department of Health and Human Services, CDC; 2019 Aug 5 [cited 2022 Jul 19]. Available from: https://www.cdc.gov/vaccines/vac-gen/additives.htm
• Public Health Agency of Canada. Immunization of immunocompromised persons: Canadian Immunization Guide [Internet]. Ottawa, ON: Government of Canada; 2022 May 9 [cited 2022 Jul 19]. Available from https://www.canada.ca/en/public-health/services/publications/healthy-living/canadian-immunization-guide-part-3-vaccination-specific-populations/page-8-immunization-immunocompromised-persons.html
• World Health Organization (WHO). Coronavirus disease (COVID-19): Vaccines [Internet]. Geneva, CH: WHO; 2022 May 17 [cited 2022 Jul 19]. Available from: https://www.who.int/emergencies/diseases/novel-coronavirus-2019/question-and-answers-hub/q-a-detail/coronavirus-disease-(covid-19)-vaccines?adgroupsurvey={adgroupsurvey}&gclid=EAIaIQobChMI5YeRsZCJ-QIVBIbICh3YNQIIEAAYASAAEgJhefD_BwE
• Centers for Disease Control and Prevention (CDC). Science Brief: SARS-CoV-2 Infection-induced and Vaccine-induced Immunity [Internet]. Atlanta, GA: U.S. Department of Health and Human Services, CDC; 2021 Oct 29 [cited 2022 Jul 19]. Available from: https://www.cdc.gov/coronavirus/2019-ncov/science/science-briefs/vaccine-induced-immunity.html
• Cavanaugh AM, Spicer KB, Thoroughman D, Glick C, Winter K. Reduced Risk of Reinfection with SARS-CoV-2 After COVID-19 Vaccination - Kentucky, May-June 2021. MMWR Morb Mortal Wkly Rep [Internet]. 2021 Aug 13 [cited 2022 Jul 19];70(32):1081-1083. DOI: 10.15585/mmwr.mm7032e1