What Are the Different Types of Vaccine?

The unprecedented COVID-19 pandemic has sent global health experts scrambling to find a vaccine. From The Imperial College London to German-based immunotherapy company BioNTech SE, human trials are starting up around the world. Depending on how research progresses, several different options could be used to develop the vaccine.

Weakening the virus

One of the most widely used vaccine development strategies is "weakened" vaccines to hinder reproduction inside the body. Vaccines for measles, mumps, rubella, chickenpox and influenza all rely on this technique. It works by introducing small amounts of a vaccine virus into the body with the capacity to reproduce less than 20 times. In comparison, natural strains of the same virus would reproduce thousands of times. This means that while the body is introduced to the virus and creates antigens to fight it off, the body is not at risk of disease. Exposure prompts the body to create 'Memory B' cells that remember the virus and can remain in the human body for decades, easily fighting off infection if it appears in the future. One of the main advantages of weakened vaccines is lifelong immunity.

Inactivate the virus

The inactivate strategy sees researchers kill off the virus with a chemical before introducing it to the body. While the capacity to reproduce and cause disease is hindered, the body still reacts to the presence of the virus and prompts the immune system to create cells that protect against disease. Vaccines for polio, rabies and hepatitis A all use this method. As the vaccine doesn't trigger even a mild form of disease it's suitable for people with compromised immune systems. One of the limitations is that several doses are required before immunity is attained.

Partial use of the virus

Another option is removing a section of the virus and using it as a vaccine. Vaccines for hepatitis B and the human papillomavirus (HPV) use this method, which relies on a partial immune response to protect against the full strain. After just two doses, lifelong immunity can be achieved.

Deactivating bacteria

Other vaccines, including diphtheria, tetanus and pertussis, rely on toxins created by disease causing bacteria. These toxins are extracted and deactivated with a chemical that eliminates the capacity to cause disease. They're then introduced to the body which encourages the immune system to create antigens, without the risk of disease.

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