There is still so much to be learned about COVID-19.

As we hit the end of the second year of the pandemic, there are various questions about the virus that health experts are looking to find answers for, one being details about the occurrence of “long COVID."

Long COVID, also known as post-COVID syndrome, is the term used by many to describe the large scope of new or continuing health issues people may endure over a month after being initially infected with the coronavirus. And yet, according to Boston University's Dr. Nahid Bhadelia, "studies so far have used different definitions of long COVID." This has made it difficult for health experts to sufficiently tackle uncertainties regarding the long-term effects of the virus.

Dr. Bhadelia did say, however, that fatigue seems to be the most frequent symptom of long COVID.

According to WebMD, symptoms of long-COVID symptoms are perhaps connected to the impact the virus has on the vagus nerve, which interacts with the parasympathetic control of the heart, lungs, and digestive tract. It plays a crucial role in many body functions, including speech, sweating, and heart rate.

A study conducted by the U.K. Health Security Agency concluded that “there is evidence that vaccinated people who are subsequently infected with COVID-19 are less likely to report symptoms of long COVID than unvaccinated people,” even after six months of initial infection. The authors of the study clarified, however, that a limitation regarding their research was the “many differences between people who are and are not vaccinated," as "there is a risk in all these studies that factors other than vaccination status may have influenced the results.”

Furthermore, scientists at the United States Department of Veterans Affairs found that the odds of developing heart disorders after recovering from COVID-19 were significantly higher in those who have been infected when compared to those who never got the disease.

Many health experts agree that there is somewhat of an absence of data regarding post-COVID syndrome, which makes it hard to study or treat. Dr. Kathleen Bell of the University of Texas says that she is "starting to see some interesting features of inaccurate attributions to COVID, both on the part of perhaps the person with long COVID symptoms and health care providers," which makes it "a little difficult to sort it out."