Vaccines are made from antigenic components, along with other chemicals that enhance its effectiveness, such as adjuvants and preservatives. Since Edward Jenner first discovered vaccination in 1769, this breakthrough has saved countless lives. Prior to the introduction of Jenner's smallpox vaccine, as many as 400,000 people in Europe alone died of the disease each year. The traditional treatment for smallpox, variolation, involved taking a sample from someone with smallpox and injecting it into someone who was susceptible to contracting the disease. Variation was risky, given that traditional medicine men deliberately injected the smallpox virus into another patient. If the dose was too high, the patient could face the full force of the disease. Jenner's vaccine, on the other hand, adopted a similar method, but much safer. Edward Jenner's vaccine was born out of the observation that milkmaids who had previously contracted cowpox did not get smallpox. Jenner decided to put this tale to the scientific test. He injected an 8-year-old boy with cowpox. After the boy recovered from cowpox, Jenner infected the boy with smallpox. The boy did not contract the disease because he became immune to it. This simple vaccine started a revolution in the world of health care that continues to this day. We have now discovered a wide range of ways to achieve immunity to disease. Jenner's strategy is now one element of a weapon that has diversified widely over years of curiosity and scientific research. So ... what vaccination strategies are available to us today? To understand what goes into a vaccine and to appreciate the nuances of our current developments, it is important to understand how the body acquires immunity against disease. Immune Response and Memory The immune system responds to pathogens (or any other foreign particles) in two broad ways. The first is a primary response, in which certain immune cells indiscriminately attack anything they identify as foreign. If this fails to neutralize the threat, the immune system calls in its more specialized troops, which marks the beginning of the secondary response. In the secondary response, T cells and B cells are recruited to fight the threat. The B-cells will produce antibodies, chemical death tags that signal the T-cells and various other immune cells to finish killing whatever is labeled with the antibody. This system is extremely efficient, but importantly for vaccination, it can recall past infections from pathogens. If the same pathogen enters the body again, the immune system can fight and finish it off more quickly. Thus, a vaccine can be anything that gives the immune system the long-term ability to fight a given disease. This brings us to the key ingredient in the vaccine-that which gives the immune system a memory of a pathogen it has not yet fought. There are various ways to develop this immunity, as will be explained below. Live attenuated vaccines A live attenuated vaccine is the way Edward Jenner's cowpox vaccine followed. As the name implies, attenuated live vaccines are live pathogens that have been attenuated so they can no longer cause disease, but are still able to stimulate the immune system. This stimulation causes the immune cells to develop a memory of the disease. A weakened pathogen can be a non-pathogenic or less pathogenic species or variant of the disease-causing organism. The cowpox virus used by Jenner belonged to the same family as the smallpox vaccine - smallpox viruses - and therefore shared molecular markers to which the immune system responded to fight the disease. So far, live attenuated vaccines have been some of the most successful vaccines in history. These vaccines create the longest memory against the pathogen; in many cases, people need only one vaccination to provide nearly lifelong immunity against the disease. Vaccines against smallpox, measles, and chickenpox, to name a few, have used live, attenuated vaccines.
Inactivated vaccine If a live attenuated pathogen is deemed not feasible for the disease (because of safety, side effects, or difficulty in creating a safe version), a dead or inactivated pathogen is administered. The pathogen is killed by heat or chemical treatment and then injected into the body. Since the pathogen is still a foreign substance and carries all the pathogenic markers, called antigens, it is able to generate an immune response and induce memory formation. They are not as effective as live vaccines in terms of providing immunity to the body, so you usually have to give several shots of a vaccine called a booster. Subunits, DNA, and genetic engineering In addition, there are vaccines that do not inject the entire pathogen. Instead, we break down the pathogen, identify the antigens on the pathogen, and then only introduce these molecules into the body. The antigen can be a sugar molecule in the pathogen, a specific protein, or, as in the case of a virus, only its capsid. We can introduce a combination of these molecules in inventive ways to stimulate the immune system exactly the way we want. There are also DNA vaccines. Here, instead of injecting the antigenic molecule itself, the DNA that encodes these molecules is injected. Some host cells will express the antigenic code in the DNA (this is abnormal but normal host cell behavior), resulting in immunization. In addition, there are new vaccine technologies incorporating various genetic engineering techniques to make vaccines safer and more highly accurate tools for fighting diseases such as cancer and HIV. Adjuvants, preservatives and more: Vaccines are not only made from attenuated pathogen or antigens in an aqueous solution. There are adjuvants, preservatives, stabilizers, antibiotics, and more to ensure the best chance of the vaccine reaching the body. Vaccine developers carefully combine the perfect formula to help the immunogenic part of the vaccine do its job. This is also the area that has been most widely discussed both in the media and in conspiracy theory circles. The chemicals used for adjuvants, the molecules that enhance the immune properties of the vaccine, are being scrutinized for their potential toxicity to the body.
Aluminum compounds are a commonly used adjuvant. This has raised public concerns about toxicity. In addition, thimerosal, a mercury-based adjuvant, has been banned by the Food and Drug Administration because of health concerns. Although such compounds are toxic to the body, the amount in the formulation is too small to cause any serious side effects. With this in mind, adjuvant research addresses potential health problems and attempts to formulate molecules that are safer and more effective than molecules used in the past. Since the "discovery" of Jenner's cowpox, vaccines have saved millions of lives over the years. There are many new technologies being tested, such as mRNA vaccines as well as adjuvants developed with recombinant technologies. These new strategies offer hope for a potential cure for viral diseases, which continue to affect a large proportion of the world's population.