Vaccination against SARS-CoV-2 reduces the risk of prolonged COVID after infection by only about 15%, according to a study of more than 13 million people1. This is the largest cohort ever used to study how many vaccines protect against the disease, but it is unlikely to end the uncertainty.

Long-term COVID – a disease that lasts for weeks or months after infection with SARS-CoV-2 – has proved difficult to test, not least because the set of symptoms makes it difficult to determine. Even finding out how often this was was a challenge. Some studies suggest that it occurs in about 30% of people infected with the virus. But a November study of about 4.5 million people treated in U.S. Department of Veterans Affairs (VA) hospitals found a total of 7 percent, lower than those who were not hospitalized.

Another mystery is whether prolonged COVID is less likely to occur after a breakthrough infection – one in a person who has been vaccinated. In a May 25 study in Nature Medicine, VA nephrologist Ziyad Al-Aly of the VA Saint Louis Health Care System in St. Louis, Missouri, and colleagues – the same team that authored the November study – reviewed VA health records from January to December 2021, including those of approximately 34,000 vaccinated people who had a breakthrough from SARS-CoV-2 infections, 113,000 people who were infected but not vaccinated, and more than 13 million people who were not were infected.

Cracks in the bumper

The researchers found that vaccination appears to reduce the likelihood of prolonged COVID in people who have been infected by only about 15%. This is in contrast to previous, smaller studies, which found much higher levels of protection. This is also a departure from another large study that analyzed self-reported data from 1.2 million smartphone users in the UK and found that two doses of the COVID-19 vaccine halved the risk of long-term COVID.

The authors of the latest study also compared symptoms such as brain fog and fatigue in vaccinated and unvaccinated people for up to six months after a SARS-CoV-2 test. The team found no difference in the type or severity of symptoms between those who were vaccinated and those who were not. “The same fingerprints we see in people who have sudden infections,” Al-Ali said.

There are more than 83 million people infected with COVID-19 in the United States alone, he said. If even a small percentage of them become long-term COVID, “this is an incredibly large number of people affected by a disease that remains a mystery.”

The limited protection provided by vaccines means that lifting measures such as mask mandates and restrictions on social distancing may put more people at risk – especially those with compromised immune systems. “We are literally relying solely, now almost exclusively, on the vaccine to protect us and protect society,” Al-Ali said. “Now we say that this will protect you only 15%. You remain vulnerable, and extremely so. ”

“Generally speaking, it’s terrifying,” said David Putrino, a physiotherapist at Mount Sinai Health System in New York who has been studying COVID for a long time. He praised the study, which was difficult to carry out due to the quantity and quality of the data, but added that it was limited because it did not break down the data into key factors, such as the participants’ medical history. “These are very important questions that we need answered,” Putrino said. “We still don’t have really well-designed research.”

Another unknown Omicron

Stephen Deeks, an HIV researcher at the University of California, San Francisco, said the study did not include data from people infected during the period when the Omicron variant caused the majority of infections. “We have no data on whether Omicron causes prolonged COVID,” he said. The results, he added, “refer to a pandemic that has changed dramatically.”

However, Deeks adds, the results point to the need for more research on long-term COVID and accelerated development of therapies. “We don’t have a definition, we don’t have a biomarker, we don’t have a imaging test, a mechanism or a treatment,” he said. – We only have questions.

This article has been reproduced with permission and has been published for the first time on May 25, 2022

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