This article was originally posted in the Montreal Gazette.
There is still a great deal that is uncertain about the persistent symptoms that we have taken to calling long COVID. Why it happens, how common it is and how to treat it are all still somewhat unclear. But a research letter recently published in the Journal of the American Medical Association provides at least some hints on how we can prevent it.
Up until now, there was ambiguity about whether vaccination prevented long COVID or not. Data from the U.S. Department of Veterans Affairs suggested that persistent symptoms were lower in vaccinated individuals, but not all the early data was entirely consistent. Part of the problem in studying long COVID is that different groups use different definitions. The U.S. Centers for Disease Control and Prevention defines it as symptoms that persist for four weeks after infection whereas, the World Health Organization uses three months after the onset of COVID infection. Depending on which definition you use, you can get very different estimates for how common long COVID actually is. The risk of long COVID is also going to differ depending on whether you consider people who were hospitalized for severe infections, people with only mild infections, or a combination of the two. When different studies use different methodologies, comparing them becomes an apples to oranges problem.
The most recent data, from researchers in Milan, provides some useful information. Researchers analyzed health-care workers from nine medical centres in Italy and compared the COVID recovery of vaccinated and unvaccinated employees. Workers were being screened for COVID every one to two weeks, so virtually all cases would have been picked up. If mild cases were to go undiagnosed, that would provide a falsely elevated estimate of long-COVID risk. Researchers also limited their analysis to non-hospitalized COVID patients, which again guarded against overestimating the risk of long COVID by mixing together milder and more severe cases.
Perhaps unsurprisingly, older patients and those with pre-existing medical conditions were more likely to have persistent symptoms one month after infection. That being said, I’ve anecdotally seen many younger patients with persistent symptoms, and it is important to remember that lower risk does not mean zero risk.
Interestingly, the risk of long COVID did not differ significantly by wave, which argues against the notion that the newer variants are less likely to cause severe disease. What did make the largest difference was vaccination status. Getting two or three doses reduced the odds of developing long COVID by 75 and 85 per cent respectively. Receiving a single dose did not. Since the data was largely derived from infections that occurred in 2021, many health-care workers had only received two doses at that time.
Intuitively, it seems logical that vaccination would reduce the risk of long COVID, and many of us assumed that would be the case. Vaccination reduces the severity of disease and also prevents infection. Despite what people say online, multiple studies have shown that vaccination with three doses plays an important role in preventing infection. While the vaccines are less protective against Omicron than they were against the Delta variant, three doses still reduced the odds of infection by 76 per cent.
Many aspects of long COVID still defy simple answers. There is no clear diagnostic test or treatment; people have very different symptoms that may not all be due to the same cause. Symptoms do improve with time, but it is hard to predict who will improve and how long it will take. The one thing we can say with slightly more certainty is that vaccination seems to reduce the risk of persistent symptoms. Of course, the best way to avoid long COVID is not get COVID in the first place, and the vaccines can help with that, too. So can wearing a mask and just being careful.