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Vaccines and why they matter

Fatma Guleid

The COVID-19 pandemic is a public health crisis on a scale which we have not witnessed for generations. For most, a vaccine is seen as the most effective way to protect everyone from COVID-19 and allow us to return to our normal lives.


Vaccines may have risen to the limelight this pandemic, but they have long shaped the landscape of disease prevention and to a larger scale, public health. Our success in eradicating smallpox and wild polio and preventing some cancers such as those of the cervix, can all be attributed to vaccines. But what are vaccines? how do they work and how are they made? As we anticipate the development of a COVID-19 vaccine, it would be worthwhile to understand just how important vaccines are and why we should all advocate for access for everyone.

What is a vaccine and what does it do?

To understand how a vaccine works, we must first understand how our bodies fight diseases. Our immune system is responsible for protecting us against diseases.  When a pathogen (a disease-causing microorganism) invades your body, your immune system recognizes it as an invader and destroys it.  But very importantly, your immune system also remembers this pathogen so that when you encounter it again, the immune system is quick to respond and eliminates it before you get sick. This is known as natural immunity.


However, your immune system can take days to eliminate the pathogen and sometimes becomes overwhelmed. This can make you ill and even cause death. This is where vaccines come in handy. Vaccines teach your immune system to recognize pathogens even before you encounter the pathogen. Vaccines contain a harmless form of the pathogen you are being vaccinated against. This pathogen is either killed, weakened or broken up into small parts. Once you are vaccinated, your immune system attacks this harmless pathogen and keeps a memory of it so that the next time you encounter this pathogen, your immune system is already trained and can eliminate it before you get sick.


A good vaccine will provide adequate and prolonged protection against the disease. The number of doses needed to achieve this varies from vaccine to vaccine.

Why are they important?

Simply put, vaccines prevent life-threatening diseases. Through vaccination, we can develop immunity without the risk of illness and death. This greatly reduces the burden of disease and mortality rates.  In addition, it is much cheaper to prevent a disease than to treat it making vaccines extremely cost-effective.


Vaccines are capable of not only protecting an individual but a whole population. When a large portion of the population is vaccinated, it becomes difficult for a disease to spread.  This is especially important because, within every population, there are individuals who cannot be vaccinated e.g. newborn babies, pregnant women and people with compromised immune systems. If these groups of people are surrounded by people who are already vaccinated and therefore cannot pass on disease, then they also gain protection.


Vaccines are also important in stopping epidemics and pandemics. They stop the chain of transmission as vaccinated individuals cannot transmit disease. This creates a protective barrier which eventually stops the epidemic/pandemic.

How are they made?

Good vaccines must meet basic criteria of safety and effectiveness. The vaccine development process is complex and usually takes many years. The first step is finding a viable vaccine candidate. This requires a good understanding of the pathogen and how our immune system responds to it. This is usually done in labs and on animal models and is known as preclinical studies. Once these preclinical studies have been concluded, we move on to clinical trials which are usually carried out in four phases to determine the safety, effectiveness and dosage of the vaccine.


Phase I

Phase I trials involve testing the vaccine candidate on a small group of healthy individuals. The goal of this phase is to evaluate the safety of the vaccine candidate, its ability to trigger an immune response, the optimal dose range and the preferred route of administration.


Phase II

Phase II trials are conducted following the successful completion of phase I trials. In this stage, up to hundreds of individuals are tested. The participants are split into two groups. One group receives the vaccine, while another receives a placebo (a placebo can be a salt solution, a vaccine targeting another disease or another substance). More safety data is collected, and the immune responses produced by the vaccine are also measured.


Phase III

During phase III trials, thousands to tens of thousands of people are tested and preferably from different countries.  As with phase II, participants are given either the vaccine or a placebo. In this phase, more safety data is collected from a larger group of people. The vaccine’s effectiveness is also measured i.e., does the vaccine prevent disease? Does it prevent infection? Does it produce a strong immune response? If the vaccine proves to be safe and effective after phase III trials, the manufacturers can then request approval from the appropriate regulatory body for licensure.


Phase IV

This is usually done at the post-marketing stage of the vaccine. The goal of the trial is to continue to monitor the safety and effectiveness of the vaccine after it has been rolled out.



Before a vaccine can reach people, it is thoroughly tested for safety. Each phase and step of the vaccine development process is under regulation and oversight by a regulatory body. Any adverse effects from the vaccine are usually reported and investigated thoroughly to ensure that the safety and quality of vaccines are upheld.


Finally, vaccines are an incredibly powerful public health tool. The best way to protect populations against disease is to make sure that as many people as possible are vaccinated. As the world awaits the COVID-19 vaccine, we face numerous challenges. As this is a global pandemic, most manufacturers are unlikely to have the production capacity to meet demand. In addition, as the geopolitical race to prioritize vaccination for its own citizens intensifies, low-income countries stand at a disadvantage. Therefore, a concerted global effort that coordinates production and distribution of a COVID-19 vaccine is needed to ensure equitable access. 

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