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Not Even Close: COVID-19 Complications Vs. mRNA Vaccine Side Effects

Updated: Mar 1, 2021

Vaccines are one of the greatest achievements of humankind, having revolutionized public health by the prevention of millions of disease cases. However, vaccines are medications like any other, meaning that they can also have potential side effects. Therefore, it is logical to make a risk/benefit analysis and wonder if the advantages of receiving a vaccine against COVID-19 are more important than their side effects or the complications of contracting the disease itself.

As an exercise to illustrate this point, we take two of the most common vaccines that are currently in use, BNT162b2 produced by Pfizer and mRNA-1273 by Moderna, and compare the side effects that have been observed during their clinical evaluation (see How clinical trials work), against the risk and severity of COVID-19 complications. Both vaccine side effects and COVID-19 complications vary according to factors such as the age of a person and the number of vaccine doses, so we do our best to consider this information by presenting a range for the likelihood of developing these issues.

Side Effects of the Pfizer mRNA Vaccine

Let us start with the Pfizer vaccine. As expected, some of the side effects can be observed at the injection site (most likely the upper arm). According to the percentage of patients experiencing them, these are most commonly pain (66-83%), swelling (6-7%), and redness (5-7%). Additional side effects can appear in other parts of the body or have a more general reaction for the person. Some of the observed ones have been fever (1-16%), fatigue (34-59%), headache (25-52%), chills (6-35%), vomiting (1-2%), diarrhea (8-11%), muscle pain (14-37%) and joint pain (9-22%). These side effects occurred more often following the second dose of the vaccine.

Side Effects of the Moderna mRNA Vaccine

A very similar situation has been observed with the vaccine produced by Moderna, with the most common local side effects being once again pain (74-89.9%), swelling (4.4-12.6%), and redness (2.3-8.9%). Some of the general effects are fever (0.3-17.4%), fatigue (33.3-67.6%), headache (24.5-62.8%), chills (5.4-48.6%), vomiting (5.2-21.4%), muscle pain (19.7-61.6%) and joint pain (16.4-45.5%).

It is important to note that many of these symptoms reflect the changes that our body undergoes while developing an immune response. This response is in place to be prepared for the next time we encounter the actual virus so that we can defend ourselves from it. On average, these symptoms lasted 1-3 days and no person was hospitalized as a consequence of being vaccinated. Moreover, the patients that sadly died during the period of these studies seem to have done so for reasons not associated with the vaccines, as a similar small number died in the group that was not vaccinated and was studied for comparison. This strongly suggests that these events were coincidental and not vaccine related. In any case, and as a measure of precaution, surveillance for potential adverse effects is planned to continue for the next two years.

COVID-19 Complications

Now, let us see how these vaccine side effects compare against actually suffering from COVID-19. The most common complications that a person with COVID-19 experiences are: fever (up to 90% of patients), cough (60-86%), loss of taste and smell (64-80%), difficulty breathing (53-80%), fatigue (38%), muscle pain (15-44%) and vomiting (15-39%). Although some of these symptoms may seem similar to the previously mentioned vaccine side effects, one of the key differences is the severity of them. Indeed, approximately 5% of patients with COVID-19, and 20% of those hospitalized, present severe symptoms that require the person to be treated in an intensive care unit (ICU). This is most commonly due to direct viral damage to the lungs and the alteration of immune responses against it, which ultimately lead to respiratory failure. Among patients with COVID-19 in the ICU, 29-91% need to be intubated in order to use a mechanical ventilator that can help them breathe, as they are unable to do it on their own.

The damage that COVID-19 causes is not restricted only to the lungs. In addition to respiratory failure, hospitalized patients can present damage to the kidneys (9%), liver (19%) and heart (20–30%), bleeding and coagulation problems (10-25%) and septic shock (6%).

As a consequence of all these complications, the risk of dying from COVID-19 for hospitalized patients is approximately 15-20%, but can go up to 40% for patients treated at the ICU. Not all people who have unfortunately died during the pandemic were tested for COVID-19, thus the number of deaths might be much higher than reported. Moreover, it has been observed that patients having survived the disease present an increased risk of developing long-term physical and cognitive health problems. Thus, a second important difference between COVID-19 complications and vaccine side effects is related to their duration. Indeed,symptoms such as fatigue, muscle weakness, sleep difficulties, anxiety and depression can persist even after six months of the initial infection. Currently it remains unknown for how long these post-COVID-19 complications can last.

In Conclusion

Taking into account all the previous points, the final piece of information that we need to know is that the two vaccines we have discussed are examples among several others that have shown to be highly efficient in giving protection against COVID-19, with some of them preventing more than 90% of cases. We strongly believe that so much suffering for the patients and their families can be avoided by the use of these preventive measures. Ultimately, the choice to be vaccinated or not against COVID-19 is up to each person. However, we do hope that after going through the science and the testimonies of people affected by COVID-19 the right choice is made.


Contributed by: Text: Armando Andres Roca Suarez, Illustrations: Armando Andres Roca Suarez & Tania Castillo

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