(ORDO NEWS) — Vaccination against SARS-CoV-2 reduces the risk of long-term COVID after infection by only about 15%, according to a study of more than 13 million people. This is the largest cohort so far used to study how vaccines protect against the disease, but it is unlikely to end the uncertainty.
Long-term COVID a disease that persists for weeks or months after being infected with SARS-CoV-2 has proven difficult to study, not least because its multitude of symptoms make it difficult to define. Even figuring out how common this disease was was not easy.
Some studies suggest that it occurs in 30% of people infected with the virus. However, a November survey of about 4.5 million people treated in US Department of Veterans Affairs (VA) hospitals suggests the figure is 7% overall, and lower among those who were not hospitalized.
Another conundrum was whether the likelihood of long-term COVID is reduced after a breakthrough infection – an infection in a person who has been vaccinated.
In a study published May 25 in the journal Nature Medicine, nephrologist Ziyad Al-Ali of the VA Saint Louis Health Care System in St. January to December 2021, including approximately 34,000 vaccinated people with SARS-CoV-2 breakthrough infection, 113,000 people who were infected but not vaccinated, and more than 13 million people who were not infected.
Cracks in the armor
The researchers found that vaccination appears to reduce the likelihood of long-term COVID in people who have been infected by just 15%. This is contrary to the results of previous, smaller studies, which found much higher protection rates.
This is also in contrast to another large study5 that analyzed self-reported data from 1.2 million UK smartphone users 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 up to six months after they tested positive for SARS-CoV-2.
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 with breakthrough infections,” says Al-Ali.
He notes that more than 83 million cases of COVID-19 infection have been reported in the United States alone. If even a small percentage of them develop into a long-term form of COVID, “that’s an astonishingly large number of people affected by a disease that remains a mystery.”
The limited protection provided by vaccines means that lifting measures such as mandatory mask-wearing and social restrictions could put more people at risk – especially those with weakened immune systems.
“We literally rely, now almost exclusively, on a vaccine to protect us and the public,” Al-Ali says.
“Now we’re saying it will only protect you by 15%. You’re left vulnerable, extremely vulnerable.”
“Generally speaking, it’s terrifying ,” says David Putrino, a physiotherapist at Mount Sinai Health System in New York who studies long COVID.
He praises the study, which was difficult to conduct due to the quantity and quality of data, but adds that it is limited because it does not disaggregate the data by key factors such as participants’ medical history. “These are very important questions that we need answers to,” says Putrino. “We don’t have one really well-designed study yet.”
Another unknown omicron
Stephen Dicks, an HIV researcher at the University of California, San Francisco, notes that the study did not include data from people who became infected during the period when the Omicron variant caused most infections.
“We don’t have data on whether Omicron causes long-term COVID,” he says. The findings, he adds, “are applicable to a pandemic that has changed a lot.”
However, Dicks adds, the findings point to the need for more research on long-term COVID and accelerated treatment development. “We don’t have a definition, we don’t have a biomarker, we don’t have an imaging test, a mechanism, or a treatment,” he says. “We just have questions.”
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