Written on 2021-04-29
Recently, I wrote about the effectivity of masks to prevent the spread of Covid-19. Today I was asked whether I would let myself be vaccinated, as my conversation partner had heard that the new mRNA vaccines were potentially problematic. As with the masking question, this isn't the first time I've been posed that question, so I think this makes a good follow-on blog post. Basically, I want to take a look at how these vaccines work, what risks are associated with them, and why I am going to let myself be vaccinated anyway.
The first vaccine was developed in the 18th century, when a British doctor called Edward Jenner showed that you could immunise people against the (very deadly) disease of smallpox by bringing them into contact with the closely related (but harmless) cowpox. (“Vaccination” is hence derived from the Latin “vacca” = “cow”.) Since then, numerous other vaccines have been developed, successfully curbing or even eradicating previously widespread and deadly diseases such as polio, meningitis, or measles.
To understand how vaccines work, one must first understand a little bit about how the human immune system works. This is a phenomenally complex system, but for our purposes a simplified excerpt will suffice. The key part we're interested in are two types of white blood cells, known as T-cells and B-cells. These cells contain receptors that can recognise and dock to pathogens, and consequently have them destroyed. Importantly, every cell can bind to exactly one type of pathogen, or more specifically, a specific structure on this pathogen. This structure is known as an antigen, and can be thought of as the pathogen's unique fingerprint.
Once a T-cell or a B-cell has bound such an antigen, a complicated reaction is launched in your body to get it ready for action. The immune system produces numerous copies of the cell that bound the pathogen, mass-producing an army of white blood cells, all of them targeted at exactly the pathogen that was detected. This reaction (possibly accompanied by a fever or other immune responses) is designed to get rid of any pathogens of this type that have gained access to the body. However, just to be on the safe side, the body keeps some of the produced white blood cells around even after the infection is over. These form a reservoir, or immunological memory, that can be used to rapidly mobilise the body's immune response should the initially encountered pathogen ever return.
The idea of a vaccine, then, is simple: create an immunological memory without making the vaccinated person seriously sick. This means one has to somehow trigger the antigen receptors without actually introducing a lot of dangerous pathogens into his or her body. The Jenner vaccine did this by using a type of pathogen (the cowpox virus) that was sufficiently similar to the targeted smallpox virus to cause a reaction, but which was not as dangerous. Most vaccines nowadays do use the “real” pathogen, but either weaken or kill it, or extract the antigen itself (remember, we only need the “fingerprint” to launch the immune response).
There are two problems here. First, if we use dead or weakened pathogens, there's still a chance we haven't killed them all - and injecting live pathogens is generally not something you want to do. Second, extracting the antigens is expensive and difficult to do on an industrial scale.
Because of this, pharmaceutical researchers have spent the past 30 years developing a new vaccination method based on mRNA. This is a very important type of molecule in your body that is used to copy genetic information from the DNA in your cells' nuclei and transmit it into the cell body (the cytoplasma), where it is then used to create the protein molecules that make up the cell.
Before we start, I should point out that I am neither a medical doctor nor a molecular biologist. As a biologist specialising in ecology and conservation, I did have several semesters' worth of undergraduate molecular biology courses, but it is not my prime area of expertise.
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