This is a really quick article just to explain why two doses of the first two COVID-19 vaccines are important and why we should not just take one and not go back for the follow up dose. If you get few side effects or no side effects, go get your second dose! The only reason you should not have the second dose is if it is recommended by a physician most times due to a life-threatening allergic reaction. Thus far there have been very few allergic reactions and none life-threatening.
The end goal of a vaccine is to create long-lasting immunity, ideally for a lifetime. For an overview of how immunity works take a look at our entire vaccine series. Some vaccines can achieve this long-lasting immunity with one shot for example the chicken pox vaccine or yellow fever vaccine others require some sort of boosting. For example children receive 5 different Diphetheria, Pertussis and Tetanus shots over the first few years of life then as adults we still get tetanus boosters every 10 years. Of course with the flu vaccine a new version is synthesised every year, this is partly because strains of flu mutate effectively enough that the old vaccine against them is not as effective. Why some vaccines require boosting and others do not is not known. Like many things in medicine we rely on the body’s natural systems to respond to our assistance. Sometimes the response is powerful and long lasting, sometimes it needs a boost or several to create that long lasting immunity.
The first shot is called a prime and the second a boost. As the words imply the prime starts the immune response and the boost amplifies it and hopefully allows it to last for a longer time. That is, antibodies exist against the virus inside your body for a number of years or a lifetime. In many ways this follows the body’s own phase by phase immune system. Therefore if you only take the first shot you would have only started the process, your immune response would not be amplified or long lasting, thereby defeating the purpose.
There are other COVID-19 vaccines in the making that only require one dose. This does not mean that they are better or worse in terms of efficacy than those requiring two. Again, we are just working with what the body allows. If clinical trials show that one dose produces an effective immune response then that’s what we work with; if two are required then that’s what we work with. The body is in charge. Similarly, trials are ongoing to determine if an increased dose will allow for a one dose regimen of the Pfizer and Moderna vaccines. We await the body’s response.
Get the prescribed dosage of whichever vaccine is available to you as soon as it’s available and let’s end this pandemic!
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M Parley 
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