Whoohoo! After a year where everything seemed to go wrong, we finally have some hope…the COVID-19 vaccine!! But as with everything in 2020, there is always a caveat – now it is vaccination hesitation. It is not surprising that after such a politicized year, people fear the vaccine is also a political tool. However, looking further into the vaccine and its current research illuminates the safety. In this post, I hope to unbiasedly answer some of the most pertinent questions regarding the coronavirus vaccine.

Essential Biology: How do vaccines protect you?

Before getting into the specifics of the COVID-19 vaccine, it is important to understand the fundamentals of vaccines and the biology behind them. Your body is under constant invasion from foreign entities, such as bacteria and viruses. Your innate immune system, which offers baseline protection much like a moat around a castle, will protect you from most of these invaders. Your innate immune system includes defenses such as skin and inflammation. But some invaders can get past ‘the moat’ and cause serious damage to the castle (you). Your body has a second line of defense called adaptive immunity, which is like generals within the castle who can adapt to the foreign invaders but require a lot of energy and resources to do so. This drain of resources by your own immune system causes many symptoms in most diseases such as a high fever and feeling tired. The white blood cells (WBCs) are the ‘leaders’ of the adaptive immune system and are called into battle when the innate immune cells bring them an antigen, or a protein from the ‘invader’ that the WBCs can use to recognize the invader. This causes many effects, including the creation of B cells, which are WBCs that create antibodies to ‘tag’ foreign invaders, and memory T cells, which are WBCs that cause ‘immune memory’ to fight this invader in the future. 

You are now protected from the invader.  But at what cost? Much like a castle that was nearly ransacked after an invasion, you have been sick for about a week and can feel drained of energy. In most cases, the invader is not too strong and you recover. However, with a severe invader you may have permanent damage or even death. Vaccines bypass this severe damage by exposing your body to an antigen without the bacteria or virus invading you. Your body develops an immune memory to the foreign invader and has a safer response upon actual exposure, much like a messenger arriving to the generals before an invasion prepares them for a possible threat.

What are the Moderna and Pfizer vaccines? Is there a difference?

The vaccines made by both companies are relatively similar. Both vaccines are 95% effective at protecting against the virus and are delivered in two shots. With both vaccines the protective benefits are strongest after receiving both doses. The second Pfizer shot is delivered three weeks after the first shot while the second Moderna shot is delivered four weeks after the first shot. There is significant data supporting that both vaccines protect against the dangerous symptoms of COVID-19. During the Pfizer vaccine trial, only one person of the 20,000 trialists administered the vaccine (there were 40,000 participants – 20,000 received the vaccine and 20,000 received a saline shot) had severe symptoms and only nine had persisting symptoms. However, it is not known if either vaccine can prevent COVID transmission (though the vaccine can protect you from getting deadly ill, you might still be able to pass on the virus to others). It is still unknown how effective these vaccines are in kids 12 and younger and how safe the vaccine is for pregnant women; however, experiments are ongoing to fully answer these questions.  There is no current evidence that these vaccines are unsafe or ineffective for either group.

What is an mRNA vaccine and is it safe?

Both vaccines are mRNA vaccines, which is a new type of vaccine. Previous vaccines include attenuated viruses (non-disease causing), inactive or killed bacteria, or segments of the virus or bacteria. Generally speaking, all of these previous vaccines contain an antigen that can cause an adaptive immune response and allow you to develop immune memory for the bacteria/virus. The new COVID-19 vaccines are unique because they actually include mRNA, a genetic message that contains information to synthesize proteins, that your cells convert into a Covid-19 spike protein, which is an antigen for the virus. At first, this can sound alarming because you are being injected with ‘a genetic message’ but there are three main reasons why you shouldn’t be so worried. First, the spike protein being made is completely harmless (that’s why it was chosen as the protein to be coded). Second, your body rapidly degrades this RNA in your cells, meaning the RNA is not around for long. Third, the RNA cannot alter or in any way impact your genetic code. This third point I want to emphasize, because it is one of the bigger fears I have heard. RNA (which is unstable and readily degraded in your cells) is different from DNA (which is very stable and is a permanent staple in your cells). All this together, plus the fact that 52 million people have been vaccinated with very few issues, really points to how this vaccine is safe. 

It is a new vaccine that was made so quickly. How can scientists know it’s safe?

I initially thought this myself; however, when I looked into the vaccine I was shocked to learn  scientists have been working on mRNA vaccines since 2003. Recently, mRNA vaccines  became a major focus for scientists because they could potentially be used to treat cancer. Also, research has already been done regarding vaccine development for other types of coronaviruses, such as the previous Middle East respiratory syndrome virus outbreak in 2012. Since the mRNA in the vaccine can readily and easily be changed, it allows these previous coronavirus vaccines to be adjusted to the novel coronavirus. Finally, COVID was heavily funded across the world in 2020. Due to these factors, when the genetic sequence of COVID-19 came out, the vaccine was readily made – most of the past year was utilized for clinical trials to ensure the safety of the vaccine.

Side effects/ questions:

Flu like symptoms:

The most common symptom is an achy arm at the injection site. However, it is not uncommon to get flu-like symptoms, which include fever, chills, tiredness, and headaches following your shot, especially the second one. These are not new vaccine side effects. As I mentioned above, your body causes these symptoms while it activates your immune system. So it is actually a good sign to have some slight symptoms because it means your body is working to protect you. As with any symptoms, if the symptoms persist for a few days or get worse, do not hesitate to contact your doctor.

Allergic reactions:

The only severe reactions to this vaccine, though very rare, have been allergic reactions. Though this is not new to vaccines, or any medical treatment for that matter, for people to be allergic to it. Even penicillin, one of the most commonly prescribed antibiotics, causes an allergic reaction in 10% of people. Though the COVID-19 vaccine has a significantly low allergy rate (0.0011%), you usually are monitored for allergy symptoms for around 15 minutes after getting the shot. If you are known to be allergic to many medicines, alert your health care provider because they will ask you to stay 30 minutes just to be absolutely sure no adverse allergic reaction occurs.

Can it make you infertile?

I’ve heard on the Internet that the vaccine can make women infertile. However, there is no scientific basis for this claim. This rumor began as a Facebook post that inaccurately conflated many medical concepts. If your immune system makes an antibody for a protein naturally found in the body, it can sometimes attack itself – this is called an autoimmune disorder. The Facebook post insinuated that parts of the COVID-19 spike protein encoded by the vaccine were similar to a human protein called syncytin-1, which is important for placental development. This was thought to cause an autoimmune reaction to the placenta and lead to infertility. This is inaccurate because an antibody is very specific for a certain exact protein, much like how you can have a similar phone number with someone else but only your phone is called when someone exactly dials your number. So it doesn’t matter if there are similar parts to a protein, because antibodies only recognize their specific antigen. 


In conclusion, the vaccine has far more science backing up its efficacy and safety than initially thought. Though it seems like the vaccine came out quickly, there has been extensive research done prior to vaccine administration and plenty of human trials. Many of the ‘side effects’ are actually induced by your body reacting to the vaccine to create antibodies. The only thing to be aware of is an allergic reaction, which is rare and why the nurse will keep you after your injection. Overall, this information fully supports the efficacy and safety of the vaccine. Together we can overcome this virus!

Peer edited by Ricardo Rivera-Soto and Yogitha Chareddy

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