The World Health Organization noted this year that anxiety and depression increased by 25% across the globe in just the first year of the COVID-19 pandemic. And researchers have continued to find more evidence that the coronavirus wreaked havoc on our mental health.

In a 2021 study, more than half of American adults reported symptoms of major depressive disorder after a coronavirus infection. The risk of developing these symptoms — as well as other mental health disorders — remains high up to a year after you've recovered.

It's not surprising that the pandemic has had such a huge impact. "It's a seismic event," said Dr. Ziyad Al-Aly, a clinical epidemiologist at Washington University in St. Louis and the chief of research and development at the Veterans Affairs St. Louis Health Care System.

Health concerns, grief from losing loved ones, social isolation and the disruption of everyday activities were a recipe for distress, especially early on in the pandemic. But compared with those who managed to avoid infection (but also dealt with the difficult impacts of living through a pandemic), people who got sick with COVID-19 seem to be much more vulnerable to a variety of mental health problems.

"There's something about the coronavirus that really affects the brain," Al-Aly said. "Some people get depression, while other people can have strokes, anxiety, memory disorders and sensory disorders." Still others have no neurological or psychiatric conditions at all, he said.

Why do some people get depressed when they have COVID?

Scientists are still learning exactly how the coronavirus alters the brain, but research is beginning to highlight some possible explanations. A few studies, for example, have shown that the immune system goes into overdrive when some people get sick. They can end up with inflammation throughout the body and even in the brain. There is also some evidence that the endothelial cells lining blood vessels in the brain become disrupted during a bout of COVID-19, which may inadvertently allow harmful substances through, affecting mental function. And cells called microglia, which normally act as the brain's housekeepers, may go rogue in some patients, attacking neurons and damaging synapses, Al-Aly said.

It's possible that COVID-19 may even compromise the diversity of bacteria and microbes in the gut. Since microbes in the gut have been shown to produce neurotransmitters such as serotonin and dopamine, which regulate mood, this change could be at the root of some neuropsychiatric issues.

Who is most at risk?

One of the biggest risk factors for developing depression after COVID-19 — or after any major illness — is having a diagnosed mental health disorder before you get sick. People who had severe COVID-19 symptoms and had to stay at a hospital during their illness also have increased chances of depression, said Megan Hosey, a rehabilitation psychologist who works with ICU patients at the Johns Hopkins Hospital.

According to WHO estimates, young people are disproportionately at risk of suicidal and self-harming behaviors after COVID. Women are more likely than men to report mental health effects after COVID. And people with preexisting physical health conditions, such as asthma, cancer and heart disease, are more likely to develop symptoms of mental disorders after COVID.

Additionally, people who experience extensive sleep disruption, social isolation or a significant change in other behaviors, such as the amount of alcohol they consume or the type of prescription medications they take, may be more likely to face depression after the physical symptoms of COVID-19 fade away. "We know that having additional stressors on your plate can predict depressive symptoms later on," Hosey said. Some studies suggest that people who experience these stressors may be more vulnerable to developing long COVID in general.

When do COVID blues become clinical depression? What are some early signs?

While you are in the thick of things, fighting off viral infection, it is normal to feel tired and headachy. "When you feel physiologically terrible, it can interfere with your mood," Hosey said. "I would never diagnose somebody with a clinical depression in the acute phases of a COVID infection."

But if your exhaustion and feeling of being overwhelmed persist for two to six weeks after your COVID infection and start to interfere with day-to-day activities or negatively affect your relationships with others, it could be a sign of depression, Hosey said.

Some people with depression may also experience persistent sadness, tearfulness, irritability, changes in appetite or weight, trouble thinking or concentrating, or feelings of immense guilt, worthlessness or hopelessness. Those with severe depression may think frequently of death and develop suicidal ideation, Hosey said.

What can you do to treat depression after COVID?

If you are concerned that you or a loved one may be experiencing symptoms of depression after a COVID infection, it's important to talk to a medical or mental health professional. "Not everyone will need to see a psychiatrist to be evaluated for depression," Al-Aly said. People can share what they are going through with their primary care doctor to get help as well, he said. "The most important thing is to seek help. And seek help sooner rather than later."

Depression is not something you can typically shake off on your own, Hosey said. It can be tempting to use online resources and self-diagnostic screening tools and to order supplements that promise to calm COVID-related inflammation or repair your gut health. But many of these interventions are not reliable or backed by evidence.

It is a good idea to take stock of your diet, sleep and drug and alcohol use. Consuming more nutritious foods and setting up a good sleep routine, for example, may have a small positive impact on your mental health. Research suggests that exercise and meditation may also help heal the mind in some cases. But if behavioral changes don't work, a professional can recommend therapy or medication, depending on your needs.

It's not yet clear how long it takes to move beyond depression symptoms after COVID. "Recovery from depression is a very individualized process," Hosey said. Many people recover after a brief course of treatment. Some people experience relapses, where their symptoms get better and worse and they may need to try a different treatment, she said. Sometimes depression resolves without treatment, though that may be more likely to happen for people with mild cases.

"In the wake of a COVID infection, you should give yourself a little bit of a break and be patient," Hosey said. "An infection can be hard to cope with."