CNN
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As a summer wave of Covid-19 infections sweeps the country, a timely new study has examined the risk of contracting long Covid and whether those risks have changed over time.
The study found that the likelihood of developing long Covid has declined since the start of the pandemic, but remains substantial, particularly for people who are not vaccinated against the coronavirus.
According to an analysis by the federal Agency for Healthcare Research and Quality released in June, about 7% of American adults, or about 18 million people, have already suffered from long Covid. Harvard economist David Cutler estimated in 2022 that the total cost of long Covid to the nation was $3.7 trillion, or 17% of the country’s pre-Covid gross domestic product.
The study, published Wednesday in the New England Journal of Medicine, suggests the human and financial costs will only continue to rise. The investigation used computers and advanced machine learning to sift through data from millions of medical records held by the Department of Veterans Affairs.
Researchers at Washington University in St. Louis and the VA Health System set out to find people who got COVID at different points in the pandemic — before vaccines were available, during the period when the Delta variant dominated transmission, and after the Omicron family of variants emerged — to see if the risk of persistent symptoms from long COVID had changed.
They also took into account vaccination status. People were considered vaccinated if they had received at least their first series of vaccines and unvaccinated if they had not.
The study looked at more than 441,000 people who contracted COVID-19 between March 2020 and late January 2022 and survived at least 30 days after infection. Their records were compared to those of more than 4.7 million people who did not contract COVID but were seen at the VA for other reasons during the same period.
The researchers found that in the first year, when the ancestral strain of coronavirus was circulating and immunity to the virus was low, one in ten people who contracted Covid had symptoms consistent with those of long Covid. Symptoms were counted across 10 disease categories as long Covid if they were new and developed between 30 days and a year after an initial Covid infection.
Vaccines have been a game changer, halving the risk of long Covid during the Delta wave that hit in the summer of 2021.
However, the risk remained high during the Delta pandemic for unvaccinated people, with about 10% continuing to have persistent symptoms after their initial infection.
During Operation Omicron, launched after Thanksgiving in 2021, 3.5% of vaccinated people developed long Covid after the acute phase of infection, compared to 7.7% of unvaccinated people.
The study has some limitations. The people treated with VA are predominantly white men, so the study population is not as diverse as the general population and its findings may not apply to everyone.
For example, a recent study found that nearly one in ten people who first contract Covid-19 during pregnancy will subsequently develop long-term Covid, an incidence that may be higher than in the general population.
The new study does not account for possible differences between people who stopped after their primary series of Covid-19 vaccines and those who continued to receive the recommended boosters to keep their immunity up to date as the virus mutated over time.
The study also doesn’t take into account the immunity people might develop after infection or reinfection, though that’s a question Dr. Ziyad Al-Aly, the study’s lead author and chief of research and development at Veterans Affairs St. Louis Health Care System, said he’s looking into as a follow-up.
Al-Aly estimates that nearly three-quarters of the decline in the risk of long Covid since the early days of the pandemic can be attributed to vaccines.
Although the cause(s) of long Covid symptoms are not fully understood, there is some evidence that people with long Covid continue to have active virus lurking in their bodies long after their initial infection.
“Vaccines actually help your immune system get rid of the virus,” Al-Aly said. “They help the immune system suppress the viral load and clear the virus faster.”
The importance of vaccination is one of the study’s key takeaways, said Dr. Hector Bonilla, co-director of Stanford’s Post-Acute COVID-19 Syndrome Clinic.
Bonilla said that when COVID vaccines became available, most people were eager to get vaccinated and doctors saw a sharp drop in the number of new patients showing up at their homes with persistent symptoms.
Now, instead of a flood, they have a steady influx of new patients into his clinic, some of whom develop long Covid after a second or third infection.
“Long Covid is a serious illness,” Bonilla said. And many people are caught off guard when they get it. But at this point, most have decided to stay up to date on their vaccines. He said more people need to understand that vaccination is a critical way to reduce the risk of long Covid.
“Vaccination remains a very important element to prevent prolonged symptoms of Covid,” Bonilla said.
After the impact of vaccination, the study found, the remaining 30% of the decline in risk over time is likely due to changes in the virus itself.
“The virus is changing, evolving, and even among unvaccinated people, it has led over time to a lower risk of developing long-term COVID-19 than during the initial period or the very first period of the pandemic,” Al-Aly said.
So, according to the latest data, about 3 out of 100 people who are vaccinated with at least their primary series and who catch Covid-19 now will suffer from long Covid, Al-Aly said.
This is an important step forward, but it still means that many people are living with disabilities or poor health.
Experts who were not involved in the study agree that a rate of 3.5% means the risk of long Covid is still substantial and serious.
“A large number of new infections and reinfections still translates into a huge number of people with long Covid,” Dr. Daniel Griffin, an infectious disease specialist at Columbia University who treats people with long Covid, said in an email.
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“Although the numbers have declined since the early days of the pandemic, we are still seeing new patients with long Covid who developed after a recent infection,” he added.
Al-Aly said this study and others underscore the need for increased funding for coordinated and ongoing care for long-term Covid patients, as well as the need for greater urgency in finding treatments.
“I don’t think the United States is doing enough to solve this problem,” Al-Aly said. “I understand the desire to move on and put it all behind us, but the fact is there are literally millions of people suffering from long Covid, and even if their numbers go down, there will always be millions more.”
“There is no real plan to address this problem, and there can’t be.”
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