COVID-19 Vaccine Side Effects: What You Need To Know

As the world ramps up measures to combat the ongoing global pandemic, the creation and distribution of COVID-19 vaccines are currently one of humankind’s biggest hopes in heading towards a new normal.

For those who have received the vaccine — whether it’s their first dose or second, whether it’s Pfizer, Moderna, AstraZeneca, or others — many reported feeling a combination of different side effects. According to the World Health Organisation (WHO), typical side effects include “pain at the injection site, fever, fatigue, headache, muscle pain, chills and diarrhea.” It also is noted that the chances of any of these side effects occurring after vaccination differ in intensity and duration according to the specific vaccine. 

In most cases, these symptoms are mild or moderate and go away on their own within a few days. Regardless, there are anomalies, as shown in clinical trials, or either more serious and long-lasting effects, or subjects who did not have any symptoms upon receiving their vaccination.

This proposes a few questions: Why do people react differently to vaccines? What specific elements in vaccines cause such side effects? And most importantly, is there a correlation between one’s side effects and their immune system? 

We sat down with Doctor Phan Vo Hanh Nguyen, currently working in the Vaccination Department of Ho Chi Minh City’s Children Hospital 1.

Why do people get side effects after getting the vaccine?

The purpose of vaccination is to take advantage of the body's adaptive immune response to create immune memory cells that are ready to respond quickly when encountering the same pathogens again in the future. Preparing your body to actively fight the pathogen upon exposure usually takes several weeks after vaccination. However, as soon as there is an entry of a foreign agent (vaccine), the innate (or natural) immune mechanism is also activated immediately, causing some — but not all — people to be exposed to the virus. The likelihood of any adverse events following vaccination and the extent of these reactions varies by vaccine and by individual. 

In addition, the excessive fear or anxiety of the person receiving the injection can also create some overreactions and can easily be confused with an allergic reaction caused by the vaccine.

What are the side effects of the COVID-19 vaccine that you’ve seen among your patients?

As with any other vaccine, side effects reported from COVID-19 vaccine were mostly mild to moderate and of short duration, rarely leaving a lasting effect. Common side effects include local reactions such as swelling, redness, pain, and itching at the injection site, or systemic reactions such as fever, chills, malaise, fatigue, headache, musculoskeletal pain, nausea, diarrhea, and loss of appetite.

A few serious adverse events that have been reported with extremely rare incidence after receiving the COVID-19 vaccine, such as anaphylaxis, low blood platelet count, Guillain-Barré syndrome (body immune system attack the nerves near the brain and spinal cord), inflammation myocarditis (inflammation of the heart muscle), pericarditis (inflammation of the tissue around the heart)… and the relationship to the vaccine has not been clearly determined yet. But we must note that these severe reactions only take up a minuscule portion of the vaccinated population.

Why do people experience different severities of side effects?

The occurrence and severity of side effects after injection depend not only on the type of vaccine but also on the person receiving the injection. 

Everyone's immune system is different and relies on many factors including genetics, age, sex, underlying medical conditions, current health conditions or medications being taken, and even microbiome. We are different, so our immune systems react differently to vaccines.

Some side effects may be associated with the use of adjuvants added to some vaccines in safe amounts, intended to trigger the immune system when a larger response is needed than that antigens can provide alone.

What ingredients in the COVID-19 vaccine cause side effects?

Any component of a vaccine (including primary antigens, adjuvants, stabilizers, antibiotics, preservatives or even substances leftover in very small amounts during manufacturing) can cause side effects

Is there a correlation between side effects and a person's immune system? For example, if I don't have any side effects, does that mean my immune system is weak, or that the vaccine is not working?

Some studies show no direct correlation between side effects and body immunity. The presence or absence or severity of a reaction after vaccination does not predict or reflect the body's immune response to the vaccine and should not be viewed as a measure of vaccine effectiveness.