We’re all familiar with the concept of vaccination and have probably been administered several vaccines since we were born. Vaccines have been waging war against diseases since the very first vaccine was discovered by British physician Edward Jenner in 1796 (he discovered the smallpox vaccine). Since then, vaccines for numerous diseases have been developed, smallpox has been eradicated, and the current number of vaccine-preventable diseases stands at 25.
First of all, let’s have a look at how vaccines work.
Vaccines are essentially substances that stimulate our immune system to produce antibodies. Antibodies are proteins that protect our body against pathogens (the deadly virus or bacteria responsible for causing infection). The important property of the vaccine is that it does not cause an infection itself, but merely elicits the production of antibodies against that specific disease.
Subsequently, if the vaccinated person encounters the same pathogen, the antibodies in the blood of the person recognize that pathogen and deal with it (either destroying it or rendering it inactive).
Now, let’s take a look at the most common types of vaccines in use today that are protecting the world against minuscule killers.
Live, Attenuated Vaccines
These vaccines are the closest thing to actually causing an infection in the body, because these vaccines are basically live forms of the pathogen! If they are live forms of the pathogen, then why do they NOT cause an infection?
The answer is simple: they have been weakened to such an extent that they are simply incapable of causing an infection (in other words, they have been attenuated). All they do is elicit an immune response in the body, stimulating the immune system to produce antibodies against the given pathogen, which would be similar to an actual infection. Given that they are a complete form of the pathogen, the immune response they elicit is very strong and the immunity they confer is often lifelong (just one or two doses are required). Vaccines are strong stuff!
On the down side, there’s a chance that the weakened pathogen may once again become dangerous and virulent (capable of causing infection). Also, people with weakened immune systems (like HIV patients) cannot be administered these vaccines safely. As for storage, these vaccines require refrigeration to remain potent (effective), meaning that they are unsuitable for transport to countries that may not possess the necessary storage facilities.
Examples of live vaccines are the MMR vaccine (for measles, mumps and rubella) and varicella (for chickenpox).
These vaccines contain the killed (inactive) form of the pathogen. This is achieved by killing the pathogen with chemicals, heat, or radiation. The great thing about inactivated vaccines is that the pathogen within is dead, so it can’t revert back to a virulent form. This makes them safe. Also, since no live microbes need to be sustained, refrigeration is not required and they can be transported in a freeze-dried form to developing countries.
It goes without saying, though, that inactivated vaccines don’t elicit the same strong immune response that live vaccines do. Therefore, many doses are required to maintain immunity, which is why people are given booster shots of these kinds of vaccines throughout their life.
Examples for inactivated vaccines are the polio vaccine (viral) and the cholera vaccine (bacterial).
By now, we are familiar with antibodies and the purpose they serve in our bodies. You should now know that the specific portion of the pathogen that these antibodies recognize is called an antigen. Subunit vaccines take advantage of this antibody-antigen specificity by only including the antigen in the vaccine.
Therefore, because the vaccine doesn’t contain other unnecessary parts of the pathogen, the chances of the vaccine having side-effects on people are very low.
The main problem with this type of vaccine is the time and effort required to actually isolate the specific antigens from the pathogen.
An example of a subunit vaccine is the vaccine against the hepatitis B virus (composed of only the surface proteins of the virus).
These are a very special kind of vaccine, as no part of the actual pathogen is used here. Instead, only the toxin secreted by bacteria (yes, this vaccine is only used for bacterial infections) is isolated and rendered inactive by treating the toxin with formalin (formaldehyde + water). These inactivated toxins are called toxoids. They are effective in stimulating the production of antibodies in the immune system, which will attach to these toxoids and block them, effectively teaching the body how to react to the real toxins.
Examples of toxoid vaccines are vaccines against diphtheria and tetanus.
Vaccines are very important tools in combating disease in a world that is coming under increasing medical stress. It’s time that we started taking vaccination very seriously in order to successfully reach a safer and healthier tomorrow.