Vaccination, historically known as inoculation, has long been practiced as a measure to protect against infectious diseases. The idea is to challenge the immune system with an active component of the pathogen – the antigen – to illicit a specific or adaptive immune response which will protect against the disease in the event of future exposure. The specific immune response employs white blood cells called B and T lymphocytes, which are triggered upon exposure to the antigen. B-lymphocytes produce antibodies that specifically target the antigen and neutralize it; T-lymphocytes recognize and attack the infected body cells. This immune response uses immunological memory to identify and process specific antigens, effectively remembering how to fight the disease, and it is this property that makes vaccines effective therapeutic tools against diseases.
The earliest records to the practice dates back to China, as early as 1000 CE., as well as to Africa and Turkey, involving smallpox inoculation, known at those times as variolation. It was based on the observation that healthy people who received grafts from pox-infected subjects developed immunity to the disease. The discovery of the first smallpox vaccine, though, is credited to the English Physician Edward Jenner in 1796 whose pioneering research on cowpox memorialized his name as founder of vaccination. Methodological advancements eventually followed with the remarkable work of Louis Pasteur who was the next to develop a vaccine against rabies in 1885. Jenner and Pasteur’s methods paved the way for further technical advances in vaccine research and development for the next two centuries.
Today, many types of vaccines are developed, some employing genetic engineering techniques, to help protect against different types of infectious disease. They vary in several aspects, including the form of the antigen or immunogen they contain (e.g. the natural whole pathogen versus a fragment of it), the potential health risks the vaccine may pose to some groups, especially individuals with critical health conditions (e.g. immune-compromised, allergic, or those who have had organ transplants), as well as their strength and how long they last. The latter factor determines the frequency of booster shots required in order to ensure ongoing immunity against specific diseases. Furthermore, based on the manufacturing process, vaccines usually incorporate non-antigen components that preserve and stabilize the vaccine, help retain the activity of the antigen, enhance the delivery of the vaccine, and improve its effectiveness.
The development of a vaccine is a time-consuming and meticulous process that involves 6 stages, each requiring a special human expertise that range from laboratory researchers to medical professionals to policymakers. These phases consist of the following:
1) exploratory, which aims at identifying the antigen;
2) pre-clinical trials which test the effectiveness and safety of the vaccine on cell cultures or in live animals;
3) clinical testing which measures the vaccine’s effectiveness and safety on human volunteers in controlled clinical trials after securing governmental and institutional approval;
4) regulatory review and approval phase, a step required to gain vaccine licensure;
5) manufacturing; and
6) quality control which involves follow up on the vaccine’s effectiveness in the population following its deployment.
Vaccines have helped control and contain serious human epidemics and pandemics throughout history, yet no vaccine is fully effective. Several determinants – biological and socioeconomic – can hamper vaccine development and effectiveness, as well as the implementation of immunization programs. Among these are safety concerns regarding the potential physiological complications that may arise in certain groups following vaccine administration, especially when considering immune compromised subjects. Individuals’ adherence to the recommended vaccine program, as well as the route of vaccine administration are important determinants of vaccine effectiveness. In addition, cultural resistance to vaccination has been among the main issues related to vaccine development since ancient times. Last but not least, the costs of a vaccine and the degree of coverage by health insurance plans (governmental or private/commercial sectors) and maintenance organizations is another crucial determinant that affects its development and implementation.
Nevertheless, vaccines have proven time and again to be one of the most effective measures we have against many pathogens and pandemics. The time taken to develop them is to ensure that they are as safe and effective as possible. In the case of an ongoing pandemic, like with COVID-19, it is imperative that people abide by safety precautions until a vaccine is ready to take in order to help minimize the health toll.
Dr. Colette Kabrita
Associate Professor, Department of Sciences, Faculty of Natural and Applied Sciences