In my previous post I mentioned how vaccines are a pretty hot topic right now and I believe people should approach this issue with an open mind, in order to figure out how vaccines work and their importance for the single individual and for the community. Then this week, casually reading some news online, I came across the news of a measles outbreak in New York and I believe it is time for me to write about vaccines and clarify their mechanism of action. Therefore today I will first talk a bit about the history of vaccines and then I will try to explain how they work to protect us from possibly lethal diseases.
Evidences show that vaccines, in the form of smallpox material inoculations, were employed as early as 1000 BC in China, as well as in Africa and Turkey, before they spread to Europe in the 1700 and, later on, the Americas. However, it was only in 1796 when Edward Jenner, a British physician, discovered and developed the first vaccination in its modern form and proved its efficacy to the scientific community. He observed and studied milkmaids who had previously caught cowpox (a very mild disease, similar to the highly contagious and often deadly smallpox), noticing that these milkmaids did not later catch smallpox. Therefore, when Sarah Nelmes contracted cowpox and went to Jenner for treatment, he decided to test his theory: he inoculated the 8 years old son of his gardener, James Phipps, with the cowpox material taken from the milkmaid. After developing mild symptoms of the disease, the young boy recovered, and about two months later, Jenner inoculated the young boy again, this time with smallpox material. The boy did not show any symptom of the disease: he was immune to smallpox (see picture below). His theory and methodology underwent medical and technological changes over the next 200 years, and eventually resulted in the eradication of smallpox.
From this point on, research started focusing on vaccines and developments rapidly followed. Antitoxins and vaccines against diphtheria, tetanus, anthrax, cholera, plague, typhoid, tuberculosis, and more were developed through the 1930s. Later on, new methods for growing viruses in the laboratory allowed for rapid discoveries and innovations, including the creation of vaccines for polio. Researchers started targeting childhood diseases: attenuated strains of measles, mumps and rubella were developed for inclusion in vaccines, reducing the disease burden greatly. The past two decades have seen the application of molecular genetics and its increased insights into immunology, microbiology and genomics applied to vaccinology: new methodologies and approaches like new delivery techniques (such as viral vectors, plant vaccines and topical formulations) are allowing researchers to move on unexplored paths. Disease targets have expanded, and research is beginning to focus also on non-infectious conditions such as allergies, autoimmune diseases and addictions.
As you just read, the first successful vaccine was developed by Jenner in 1796, who also coined the word “vaccination”, that derives from the Latin root vaccinus, meaning cow or derived from a cow. But how does a vaccine help our bodies to fight a disease? Basically, vaccines are our immune system trainers, preparing the body to fight diseases without exposing our body to disease symptoms. Therefore, when we come in contact with bacteria or viruses, our immune system can produce antibodies (protein molecules) that can fight the bacterium or virus threat and protect us against further infections. Our body can produce millions of antibodies a day, fighting infections so efficiently that people never even know they were exposed to an infectious threat. However, the first time the body faces a particular infection, it can take several days to produce this antibody response. For some diseases, like for example the measles, a few days to produce antibodies is too long: this infection can spread and kill the person before the immune system can fight back. That is the reason why we need vaccines.
Vaccines are made of dead, weakened or even parts of bacteria and viruses that can not cause an infection, but the immune system still sees them as threats and produces antibodies in response. However, after the “fake infection” has passed, our immune system keeps a memory of the threat and when the body encounters that infectious threat again, it can produce antibodies fast and defeat the infection before it’s too late. Vaccines also work on a community level: some people can’t be vaccinated (people without a fully-working immune system, new-born babies and elderly people, people on chemotherapy treatment whose immune system is weakened and so on), but if everyone around them is vaccinated, unvaccinated people are protected by something called herd immunity. In other words, when a high percentage of the population is vaccinated, it is difficult for infectious diseases to spread, because there are not many people who can be infected. For example, if someone with measles is surrounded by people who are vaccinated against measles, the disease cannot easily be passed on to anyone, and it will quickly disappear again (see picture below).
Despite the evidence of health gains and diseases eradications from immunisation programmes, there has always been resistance to vaccines in some groups. For example, already back in the late 1970s and 1980s, there was an increased litigation and decreased profitability for vaccine manufacture, which led to a decline in the number of companies producing vaccines. Unfortunately, the legacy of that years continues to the present day in supply crises and continued media efforts by a growing vociferous anti-vaccination lobby, allowing for diseases outbreaks as the one that was going on in New York.