What you need to know about vaccines and how they work

Over the last two centuries, people have been protected from the plague of infectious and deadly diseases through the refinement of the vaccine producing process and mass vaccinations. Before the existence of preventive methods and effective therapies, infectious diseases such as measles, diphtheria, smallpox, and pertussis topped the list of childhood killer diseases across the world. Fortunately, many of these devastating diseases have been contained because of the development and widespread distribution of safe, effective, and affordable vaccines. 


The term vaccines and vaccination are derived from variolae vaccinae the scientific name for cow pox disease. The terms were first used by an English Doctor, Edward Jenner, who developed the concept of vaccines and created the first vaccine against smallpox using exposure to the cowpox virus in 1796. 

By definition, a vaccine is a suspension of live, usually attenuated or inactivated microorganisms typically bacteria or viruses or fractions of viruses administered to induce immunity and prevent infectious disease. A vaccine provides the recipient with an acquired active immunity to a particular infectious disease. It typically contains an agent that resembles the disease-causing microorganism that it targets and is often made from weakened or killed forms of the microbe, its toxins or one of its surface proteins. The agent in a vaccine preparation works by stimulating the body’s immune system to recognize the agent as a threat, destroy it, and to further recognize and destroy any microorganisms associated with that agent that it may encounter in the future. The immune system then builds a defence mechanism against the offending microbe and its protein coat, as well as any other associated microbes. This defence mechanism is stored in the memory of the immune system of the recipient. When the recipient is exposed to the virulent form of the microbe in the future, the immune system is able to recognize it and is ready to respond by first neutralizing the microbe or its surface protein before it can enter the cells. Secondly, the immune system also destroys any cells that may have already been infected by the microbe, thereby further reducing the infection and limiting the effects. Vaccines are commonly administered via an injection on the arm. 

Vaccine Administration

Vaccines can be administered to prevent a future infection or reduce the effects of the infection if it does occur. They can also be administered to fight the effects of a disease that has already occurred. An example of this type of vaccine is the preparation used in the treatment for some forms of cancer such as bladder cancer, prostate cancer and skin cancer.

Some vaccines can offer a lifetime immunity to the disease it is designed for, and offer full sterilizing immunity by completely preventing future infections. Some vaccines, however, only provide a mitigating effect to the disease once the infection occurs. Vaccines generally provide a safe and effective way to fight and eradicate infectious diseases. Nonetheless, there are some limitations to the effectiveness of vaccines, and this is due to two main reasons:

  • Vaccine related failure
  • Host related failure

Vaccine related failure can result from a failure of attenuation of the disease causing microbe used for the vaccine or poor vaccination administration regimes. Attenuated vaccines are made from devitalized live microbes and if the attenuation process is not stable, the microbe may be able to cause infection in immunocompromised individuals. Vaccinations need to be conducted in specific time frames and if this is not followed strictly it may cause an inadequate immune response development rendering the vaccination ineffective.  

Host related failure results from a number of issues, all associated with the recipient’s immune response. A poor immune response to a vaccine can be as a result of the poor nutritional status of the recipient, age, a poor immune system or genetics. In this case, even if the recipient develops antibodies against the infection, the protection developed may not be adequate in that the immunity might not develop in time to be effective, or the antibodies produced may not be able to destroy the microbe completely. Another reason could be that the infection might be caused by multiple strains of the microbe, all of which may not be susceptible to the effect of the developed antibodies.

Even with these limitations, a partial, late or weak immunity gained from a vaccine often reduces the severity of an infection and results in lower morbidity, lower mortality rate and a faster recovery rate.

Adverse reactions to vaccines 

Vaccines are generally safe. Any adverse reactions or side effects are also typically mild. Some common side effects of vaccines include fever, pain at the injection site and muscle ache. However, some individuals develop an allergic reaction to some ingredients in the vaccine, and this can sometimes be quite serious.

Severe side effects are rare. Individuals that experience severe side effects usually have underlying conditions that make them susceptible to the disease infection, or are allergic to some ingredients in the vaccine preparation. 

Types of vaccines

Attenuated vaccines are made from active viruses and other microbes that have been cultivated under conditions that disable their virulent properties to produce a broad immune response. Examples are the yellow fever vaccine, measles vaccine, mumps vaccine, rubella vaccine and the plague vaccine. Attenuated vaccines have the advantage of producing a long-lasting immune response but may not be safe for immunocompromised individuals.

Inactivated vaccines are produced from inactivated but previously virulent microbes that have been destroyed with chemicals, heat or radiation. Examples are the polio vaccine, hepatitis A vaccine, rabies vaccine and influenza vaccines.

Toxoid vaccines are prepared from inactivated toxic compounds that cause illness rather than the microbe. Examples are the vaccines for tetanus and diphtheria. 

Heterotypic vaccines are created from pathogens of other animals that either do not cause disease in humans or only cause a mild form of disease. An example is the use of cowpox virus to develop an immunity against small pox and the BCG vaccine against tuberculosis made from the bovine microbe mycobacterium bovis.

Vector vaccines use a safe virus to carry pathogen genes that produce specific antigens such as surface proteins to stimulate an immune response in the recipient. 

Ribonucleic Acid (RNA) vaccines are composed of the RNA of the microbe packaged within a vector, such as nanoparticles. An example is the COVID-19 vaccines made by Pfizer and Moderna. 

Production of vaccines

Vaccinology is the study of the science of vaccine development and production. On average it takes about 12 months to produce a vaccine that has passed all the necessary safety tests. The production process is often complex and involves a lot of quality controls to ensure safety. The quality and safety testing takes up about 70% of the time it takes to develop and manufacture the vaccine.

All the vaccine ingredients, production processes and testing methods have to comply with strict manufacturing practices. Also, appropriate and adequate infrastructure needs to be in place to ensure the purity, sterility, efficacy and unique identity of the vaccine. Depending on the nature of the target microorganism causing a particular infectious disease, it can sometimes take more than 36 months to produce a safe vaccine for mass distribution. Other times, as in the case of the Malaria parasite or the virus that causes HIV/AIDS, the complex nature of the organism and its ability to keep mutating makes it quite difficult to develop a vaccine that will be effective in the long term.


The administration of vaccines is termed vaccination. It is currently the most effective method to curb the spread of infectious diseases. Vaccination is responsible for the widespread immunity and eradication of small pox, one of the most highly contagious and deadly disease ever to affect humans. Vaccination is also the reason for the low incidence of diseases such as polio, mumps, rubella, measles, chicken pox, tetanus, and typhoid. Numerous studies have been conducted to verify the efficacy of vaccines and there is clear, unequivocal evidence to support this. 

The effectiveness of vaccinations depend on the following:

  • Vaccines can only be produced for some type of diseases but not others. This is because sometimes the microbe causing the disease is difficult to target as it changes and adapts to developed therapies. Examples are Malaria and HIV/AIDS.
  • Some vaccines are only effective against a particular strain of the disease causing microbe. As such, some recipients can still develop a disease infection when exposed to a different strain of the microbe in the future.
  • Vaccinations work best if the administration regime is followed strictly.
  • Some individuals do not produce an immune response after being vaccinated. They are referred to as non-responders. These individuals can develop the disease infection even after receiving the vaccine. Sometimes age, ethnicity or genetic predisposition can have similar effects on the immune response.

As long as many people in a community are vaccinated, it is much more difficult for an outbreak of a disease to occur and spread. The effect of mass vaccinations is called herd immunity. Herd immunity can be achieved when over 70% of the population has been vaccinated. As a result, the whole community is protected, not just those who have been vaccinated.

COVID-19 and the available vaccines

It was possible to develop the COVID-19 vaccines in a very short period of time because most of what was required to do so was available, and those that weren’t become quickly available as the pandemic gained grounds. A lot of resources were freed up by many governments to facilitate research into finding a vaccine quickly. The length of time it takes to test the vaccine was further reduced as many people came forward to volunteer for early testing. The prevalence of the disease also allowed for a shorter trial period.

Another factor that aided the quick development of the vaccines was that there was already research available to build on, as work on the Severe Acute Respiratory Syndrome (SARS) disease and Middle East Respiratory Syndrome (MERS) disease are caused by viruses similar to the COVID-19 virus had already been done in previous years when those diseases broke out. The viruses that cause these three diseases all belong to the same family of coronaviruses. The mRNA technology for making the COVID-19 vaccines already existed, as research had been going on for decades prior to the outbreak. The Coalition for Epidemic Preparedness Innovation (CEPI) was formed in 2005 due to the outbreak of Ebola in some countries in Central and West Africa and works to accelerate the development of vaccines against emerging infectious diseases. It is a global partnership of public, private, philanthropic and civil society organizations. CEPI supported various stakeholders to work together seamlessly in the race to develop vaccines that are safe to administer in the shortest time possible. The internet also made it easy for researchers around the world to collaborate, resulting in faster positive outcomes.

Vaccination is the surest way to stop an infectious disease from breaking out and spreading. Vaccines are safe for use. The science behind them proves it. So don’t be afraid to get vaccinated.

Don’t forget to social distance, wear a nose mask and wash your hands or sanitize them frequently.  Let’s work together to stop the spread of COVID-19. Get vaccinated!


  1. Alexandra Minna Stern and Howard Markel, The History Of Vaccines And Immunization: Familiar Patterns, New Challenges health Affairs, Volume24, Number  361. DOI 10.1377/hlthaff.24.3.611 ©2005 Project HOPE–The People-to-People Health Foundation, Inc.
  2. https://www.healthline.com/health-news/heres-how-it-was-possible-to-develop-covid-19-vaccines-so-quickly
  3. https://www.who.int/news-room/q-a-detail/vaccines-and-immunization-what-is-vaccination
  4. https://www.britannica.com/science/vaccine
  5. https://en.wikipedia.org/wiki/Vaccine
February 4, 2022