Recent Studies Help Explain Long Covid

In two new studies, scientists report on symptoms, frequency, and other implications of long Covid

Tempted as we are to pretend it’s over, the Covid pandemic is still going — and, quite frankly, still thriving. In the U.S. the daily toll is inching back up toward 500 deaths per day. Globally, according to the Johns Hopkins University pandemic tracker, we have surpassed 590 million total cases.

For millions of people, surviving Covid isn’t the end of the story. Long Covid is a condition with a perplexing range of symptoms that can last for months or even years after the acute phase of the infection is over. Public health experts are increasingly alarmed about the long-term disease burden of long Covid.

Recently, new studies have shed light on it. While there is still much to learn, these studies are important steps in helping physicians and patients understand these hard-to-explain cases. Let’s look at key highlights from those studies.

How frequent is it?

A large, peer-reviewed study conducted in the Netherlands aimed to more precisely quantify the prevalence of long Covid, a condition that affects both people who had severe Covid symptoms as well as those who were asymptomatic. Just having the infection is enough to put someone at risk of long Covid.

In this study, scientists pored through data reported by more than 76,000 participants, some 4,000 of whom were diagnosed with Covid. They determined that for every eight adults with Covid, one would go on to have long Covid.

It’s worth noting that the patient reports used for this study were completed prior to the emergence of Omicron. The prevalence of long Covid among people with more recent strains of the virus may be different.

What are the symptoms of long Covid?

While some dangerous long-term effects of long Covid have already been reported, these new studies reveal a wide array of symptoms that people who have been infected with Covid should know about.

In the Netherlands study, common symptoms noted at least three months post-infection included chest pain, breathing difficulties, muscular pain, loss of taste or smell, fatigue, feelings of heaviness or tingling in the arms or legs, feeling alternately hot and cold, and the sensation of a lump in the throat. All of these symptoms were compared to responses from healthy patients to ensure that the final list was only characteristic of people with long Covid.

Many other studies of long Covid have also linked the condition to cognitive function symptoms such as brain fog. These symptoms were not studied in the research done in the Netherlands.

Who has long Covid?

In a separate study, this one recently posted as a preprint that has not yet gone through scientific peer review, researchers from Yale University and Mount Sinai’s medical school in New York gathered an impressive array of data about more than 200 participants, approximately half of whom had long Covid. One of their goals was to assess various ways to diagnose long Covid, which could help ensure that patients get the care they need.

According to their findings, there are a number of ways to identify people with long Covid. Simply paying attention to patient-reported outcomes correctly identified long Covid patients 94% of the time. Tracking antibodies and other immunological data was useful too: the team used a machine learning model to predict long Covid cases from this information.

Perhaps most interestingly, though, was the team’s discovery that low levels of cortisol were the single strongest predictor of which patients had long Covid — and of how bad their symptoms would be. Cortisol is a hormone typically produced to regulate the body’s response to stress. If this discovery is replicated in other, larger studies, it could pave the way for use of cortisol levels as a reliable biomarker to identify people with long Covid and offer them a clear prognosis.

What other effects does long Covid have?

Consistent with previous reports from patients with acute Covid infections, the Yale and Mount Sinai team found strong evidence that patients with long Covid also suffered from the reactivation of viruses they’d had before but had gone dormant. These include Epstein-Barr virus, which was recently identified as a likely cause of multiple sclerosis, and Varicella zoster virus, which is responsible for chicken pox and shingles.

The scientists note that additional study will be needed to fully understand what’s going on here, but they theorize that these viral pathogens may be exploiting the physiological chaos produced by long Covid to become more active in ways usually not allowed by a healthy immune system.

Each time someone contracts a Covid infection, that person is at risk of developing long Covid. As scientists continue to chart the effects of this condition — which in some cases becomes truly debilitating — it is important for the public to understand the true long-term risks they may face. The CDC’s latest relaxation of quarantine and other protocols could increase infection and reinfection rates, putting even more people on the path to long Covid.

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