A 15-year-old British girl who survived a nasty bout of COVID-19 has come out the other side with a "completely different personality", her mother says.
The cause is believed to be a little-understood complication that can arise in COVID-19 patients when they're seemingly on the recovery, especially children.
Nia Haughton was hospitalised in early April 10, spending two weeks on a ventilator, reports NBC News. Several days into her recovery she fell unwell again - but rather than her lungs, the virus was now attacking her brain.
"I couldn't tell what was real," she told NBC News. "It was really scary. I could hear voices. It was very traumatic."
She's not the first COVID patient to report seeing visions and having delusions - in May, The Atlantic spoke to patients in the US having similar experiences thanks to COVID-19.
Nia was having seizures too, and had to go back into intensive care where she was diagnosed with encephalitis - brain inflammation.
"I don't know which was scarier - her being on the ventilator not being able to breathe, or the fact that she came out of it with a completely different personality," Nia's mother Justina Ward told NBC News.
Nia's mental state appeared to regress into childhood, both her voice and behaviour changing.
"I think that COVID has taught us that every time we feel complacent, that we know the spectrum, a new spectrum sort of evolves," said paediatric neurologist Ming Lim, who treated Nia.
"We worry that the long-term effect would be in essentially brain growth."
While children are far less likely to die or show symptoms of COVID-19 than adults, they appear to be particularly at risk of a related condition dubbed multisystem inflammatory syndrome in children (MIS-C). The direct cause of MIS-C hasn't been confirmed, but it's believed to be the same virus - SARS-CoV-2 - that causes the typical respiratory symptoms of COVID-19.
A recent study also found children carry far higher viral loads than adults, despite their lowered risk of being symptomatic or serious illness. Contrary to US President Donald Trump's recent claims, they are far from being "almost immune".
One doctor NBC News spoke to called the growing number of cases of neurological effects a "secondary pandemic" that will impact victims for years to come.
"A fair number of people who get this disease wind up with some neurological manifestations, and these range from very mild to severe life-threatening conditions," said neurologist Robert Stevens.
"People who survive will recover from the respiratory failure, they'll recover from the kidney disease, but the imprint on the brain is likely to be much more long-lasting."
More than 716,000 people have now been killed by the SARS-CoV-2 virus.