Alexandra Ferguson
(CNN) — Having a severe case of Covid-19 appears to be linked to a higher risk of later mental illnesses, such as depression and anxiety disorders, and a new study finds the association is stronger among people who have not been vaccinated against the disease.
In the study, published Wednesday in the journal JAMA Psychiatry, the incidence of mental illness was highest in the weeks after a Covid-19 diagnosis, but the increase in incidence was much smaller in people who had been vaccinated against the coronavirus compared with those who were not vaccinated. Among people who were not vaccinated, the elevated incidence of mental illness was highest up to a year after a severe Covid-19.
The study also found that the elevated incidence of mental illness was higher and lasted longer if a person was hospitalized for COVID-19, compared to not being hospitalized for COVID-19.
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“The main surprise was that the association of COVID-19 with subsequent mental illness seemed restricted to severe COVID-19 leading to hospitalization. There was little association of COVID-19 that did not lead to hospitalization with subsequent mental illness,” said Dr. Jonathan Sterne, an author on the study and professor of medical statistics and epidemiology at the University of Bristol Medical School, in an email.
The researchers, from the University of Bristol’s School of Medicine and other UK institutions, also found stronger associations among older adults and men, compared with younger age groups and women.
“The most likely explanation for the stronger associations in older adults is that they are more likely to develop severe COVID-19 leading to hospitalization,” Sterne said. “This may also explain the somewhat stronger associations in men, but we don’t have a definitive explanation.”
The new study included electronic health record data from three groups of adults, aged 18 to 110, in England. One group included about 18.6 million people who were diagnosed with Covid-19 between January 2020 and June 2021, before vaccines were available.
People in the other two groups, which included about 14 million vaccinated people and about 3.2 million unvaccinated people, were diagnosed with COVID-19 between June 2021 and December 2021.
The researchers looked closely at how many people in each group were diagnosed with mental illnesses in the weeks after their Covid-19 diagnoses. These illnesses included depression, general anxiety disorders, post-traumatic stress disorder, eating disorders, addiction, self-harm, suicide and other serious mental illnesses such as schizophrenia, bipolar disorder and psychotic depression.
Overall, depression was the most common mental illness included in the study.
Researchers found that the incidence of depression in the four weeks following a COVID-19 diagnosis was 1.93 times higher among people who had COVID-19 before vaccination, 1.79 times higher among the unvaccinated group, and 1.16 times higher among the vaccinated group.
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The overall incidence of depression remained elevated for 28 weeks, and up to 102 weeks specifically in the group that had Covid-19 before vaccines were available, the data showed.
People who were hospitalized with severe COVID-19 had the strongest association with depression. Among those who had COVID-19 before vaccines were available, the incidence of depression was 16.3 times higher after a COVID-19 diagnosis if the infection required hospitalization, compared with 1.22 times higher without hospitalization.
“Our findings have important implications for public health and mental health service delivery, as severe mental illness is associated with more intensive healthcare needs and longer-term adverse health and other outcomes,” Dr. Venexia Walker, a senior research fellow in Epidemiology at the University of Bristol and one of the study’s lead authors, said in a news release.
The new study comes amid a major surge of Covid-19 in the United States. Levels of viral activity in wastewater have reached the highest level recorded for a summer surge since July 2022. And the U.S. Food and Drug Administration (FDA) is expected to soon give the green light to updated Covid-19 vaccines for the fall and winter season.
But the new data may not reflect the current climate, said Dr. Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center, who was not involved in the research.
“It’s a study that only looks at individuals in 2020 and 2021, in the early days of the pandemic, before omicron. So the applicability of this data to the current epidemic is unclear, because in 2024, we have a much higher level of population immunity; most people have been infected or vaccinated multiple times,” Barouch said.
“It’s a very different population now than it was in 2020 and 2021. So while this work is interesting and important, it really reflects a population at a different time in the pandemic, when people’s baseline immunity was very different,” she said. “It’s really unclear to what extent this data is applicable to the current epidemic that we have in 2024.”
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The new research is not the first to show that Covid-19 is associated with an increased risk of mental illness, said Dr. Ziyad Al-Aly, a clinical epidemiologist at Washington University School of Medicine in St. Louis who was not involved in the work but has studied mental health outcomes in people with Covid-19.
“I think the picture that emerges from this work is clear, and it is in line with what we have learned in recent years about the effect of COVID on the brain, which is that it leaves its mark on the brain, and here, that is in the form of various mental health disorders,” Al-Aly said.
The higher incidence of mental illness that appears to be associated with severe COVID-19 may be a consequence of the infection itself or could simply be due to hospitalization. Other research suggests that hospitalizations for any serious illness may be associated with a higher long-term risk of new mental health diagnoses.
While the new study doesn’t answer the question of whether the association is due to Covid-19 specifically or being severely ill in general, Al-Aly said he suspects both factors play a role.
“When people are hospitalized, they don’t eat well, they don’t sleep well, it’s an unfamiliar environment for them, it’s enormously stressful. Does it put some people at risk for depression or stress disorders and all that? Absolutely yes,” he said.
But in a paper published last year in The Lancet Infectious Diseases, Al-Aly and his colleagues found that among more than 92,000 people, those hospitalized with Covid-19 were at increased risk for several mental health problems, while those hospitalized with influenza were not at increased risk.
“We found that people who were hospitalized for COVID were at much higher risk for severe neurological problems, including neuropsychiatric disorders, including mental health problems,” Al-Aly said. “When you do a head-to-head comparison, people who were hospitalized for COVID versus people who were hospitalized for influenza, it’s very clear that it’s something kind of unique or peculiar to COVID that drives a higher risk for neuropsychiatric problems.”
