In the very beginning of vaccine production, the method used was somewhat more primitive than the advanced science we use nowadays. Smallpox was the first illness that a vaccine was produced for, as a physician called Edward Jenner noted that milkmaids who had caught cowpox from their herds could not then catch the deadly smallpox. In fact, the term vaccine is derived from the latin vaccinus, meaning ‘of or related to cows’. Jenner injected people with a small sample of cowpox, and noted that these people would also become immune to the deadly version of the disease. The first vaccine had been created.
What is a vaccine?
The breakthrough that exposure to a less harmful version of a dangerous virus or bacteria can produce immunity is the basis of all vaccines. When the body is exposed to a foreign microbe, such as a bacteria or virus, the immune response is triggered. The parts of the microbe that triggers this are called antigens. To create a vaccine, you must produce antigens of the harmful microbe you want to protect against. Once the body has been in contact with these, the immune system produces antibodies specific to these antigens that attack any cells containing them.
This response needs to only happen once, and the body will ‘remember’ these antigens in the future, so can mount the attack much faster, killing off any unwanted cells before they have time to multiply. And thus, you have immunity. The trick, though, is to create this immune response without contracting the harmful disease in the first place. There are a couple of ways to do this.
Live attenuated vaccines
The first way to produce these antigens is to grow the virus in a cell culture. Large vats of living cells are purposefully infected with the virus, which multiplies thousands of times inside them, helped along by a growth medium containing various nutrients such as amino acids, proteins and minerals. These viruses are then extracted and purified from the host cells, which is called a live attenuated vaccine.
The important difference between these viruses and the deadly virus it is a strain of, is that they have been modified so it not harmful to humans any longer. This is achieved either by being grown over many generations in non-human cells, like chicken cells, so they have mutated in such a way that they are no longer harmful if they infect a human. Another way is for them to be grown at very low temperatures, until again they have mutated so that they can only replicate properly at these low temperatures rather than in the warm temperature of the human body.
They will very briefly replicate once they are injected into the body, which triggers a huge immune response, meaning you need a much lower dose of these vaccines. It is highly unlikely that the host will develop the active disease, due to the mutations the virus has undergone to make it less harmful, and because it cannot replicate as fast as it would need to. Vaccinations that use the live attenuation technique are those such as measles, mumps and rubella (MMR) and chickenpox.
Inactivated vaccines
These vaccines are produced in the same way as the step above, but with an added final step to kill the live virus. This is achieved using heat or a chemical treatment to destroy the virus’ proteins and DNA. As dead viruses are unable to replicate, a much lower level of immune response is triggered by injecting these type of vaccines, which is why need a higher dose over a longer time, occasionally having to have top-ups after a certain amount of time to maintain immunity. The flu shot, polio and Hepatitis A use inactivated vaccines.
There are other, more complicated ways of producing vaccines, such as combining various bits of microbes rather than using one whole virus, to protect against multiple pathogens all at once. The way to produce vaccines for bacteria is very similar, although they don’t need a host cell to grow in – they can grow by themselves in the growth medium before being inactivated for use as a vaccine.
All of this is done to protect people from dangerous illnesses and diseases, which has been highly successful up to now. The risk of developing these diseases having been given the vaccine is negligible, so everyone who is offered a vaccine should feel privileged that they are in a part of the world that this life-saving preventative medicine is available to them.
