A new set of complications has come to light in children who overcome a somewhat mysterious inflammatory syndrome while infected with the coronavirus.
Early research suggests the coronavirus is mild in four out of five cases, with children in particular rarely becoming seriously ill.
Nevertheless, NHS doctors were told to look out for signs of "multi-system inflammation" early in the outbreak, after intensive care units in London saw eight children with unusual symptoms, some of whom tested positive for the coronavirus.
Medics have likened the mysterious inflammation to atypical Kawasaki disease; a rare condition that usually affects children under five and causes blood vessels to become inflamed, leading to heart complications in around a quarter (25%) of patients.
To better understand the newfound syndrome, scientists from Great Ormond Street Hospital (GOSH) in London analysed 50 children who were diagnosed with the inflammatory disorder between 1 April and 22 June 2020.
The children were followed over the next 60 days, during which time nearly a third (30%) had persistent voice abnormalities, swallowing difficulties, or a muted sense of smell or taste.
This is despite the symptoms being "significantly present" in just 8% of the children.
Although unclear, the coronavirus may directly infect nasal and throat tissue, which express the protein the infection binds to. The immune response to the virus may also lead to inflammation that affects many parts of the body.
Watch: Coronavirus can cause inflammatory syndrome in children
On 1 May 2020, the UK Royal College of Paediatrics and Child Health defined so-called "paediatric inflammatory multi-system syndrome temporally associated with coronavirus" (PIMS-TS) as a persistent fever, inflammation and "evidence of single or multi-organ dysfunction".
This could occur alongside a positive or negative coronavirus test, providing any other "microbial cause" is ruled out.
While cases of the inflammatory syndrome have spiked during the pandemic, not everyone with the condition swabs positive for the coronavirus. Some have suggested this may be due to false-negative results.
To better understand the lingering complications PIMS-TS patients may face, the GOSH scientists analysed 50 children, average age 10, who "met the case definition" for the syndrome.
Of the 50 patients, 12 tested positive for the coronavirus, while 42 had infection-fighting antibodies in their blood, suggesting the pathogen had already been overcome.
More than three-quarters (76%) of the children were admitted to intensive care, while over a third (36%) required mechanical ventilation.
Results, published in the journal JAMA Otolaryngology – Head & Neck Surgery, reveal eight (16%) of the 50 children were reviewed in a "voice multidisciplinary team clinic".
One in 10 (10%) also required "ongoing voice therapy" for abnormalities, usually hoarseness.
Further investigation revealed three (6%) had "post-inflammatory changes" to part of the voice box.
A similar proportion (4%) had "unilateral vocal cord palsy"; weakness on one side.
Weakness to both of the vocal cords and the voice box's muscles affected 2% of the children.
The same proportion of patients (2%) endured abnormal thickening to the front of one of the vocal cords; "congested" tissue that lines the nasal cavity on one side; or "unilateral atrophic vocal cord" – wasting away of the tissue on one side.
When it came to swallowing, three (6%) required ongoing therapy due to difficulties.
Two (4%) of the children who had their swallowing assessed at the start of their ill-health episode later showed signs of "incoordination and weakness" at the oropharynx; the middle part of the throat just behind the mouth.
Another (2%) who had their swallowing assessed early on later had "residual thickened fluids" coating part of the throat.
Loss of taste or smell is one of the tell-tale symptoms of the coronavirus.
The GOSH study describes how four (8%) of the children were treated with intranasal steroids for 14 days to boost their muted senses.
Despite the therapy, the patients endured dysgeusia – when food tastes unusually sweet, sour, bitter or metallic – for more than six weeks, which eventually improved.
Three (6%) of the children had an MRI scan to try and get to the bottom of their muted senses and dysgeusia, "with no specific findings to account for these symptoms".
Although unclear why these symptoms and complications occur, the nasal and throat tissue may be damaged by mechanical ventilation, where a tube is inserted into the airways.
Further research is required to uncover whether certain children are more at-risk of the inflammatory syndrome, for instance those with an ethnic minority background.
"Because the long-term sequelae of this disease are unknown, it is prudent for children with a history of PIMS-TS to be re-evaluated by the infectious diseases team within 12 months and referred to otolaryngology for any persistent symptoms," wrote the scientists.
Watch: What is long COVID?
What we know about the coronavirus-inflammatory syndrome
Medics have likened the inflammatory syndrome to Kawasaki disease, which commonly causes a rash, fever, and red hands and feet.
Kawasaki disease is thought to come about when the immune system over-reacts to an infection. Left untreated, the heart complications can be fatal in 2% to 3% of patients.
Scientists from the New York University Grossman School of Medicine have previously noted "significant clinical overlap exists" between Kawasaki and the coronavirus-related inflammatory syndrome.
The latter, however, "has been characterised by more widespread systemic inflammation and higher rates of acute complications, including cardiogenic shock"; when the heart suddenly cannot pump enough blood to meet the body's needs.
The inflammatory disorder has also been likened to toxic shock syndrome (TSS).
Often associated with tampon use, TSS is a medical emergency that can lead to fever, flu-like symptoms, nausea, vomiting and difficulty breathing.
Experts have warned these symptoms are a sign the body is overwhelmed as it tries to fight an infection.
While the inflammatory syndrome may sound alarming, the vast majority of children are said to recover with hospital treatment, with experts repeatedly stressing there is no need to panic.
The Royal College of Paediatrics and Child Health previously advised parents call 999 or take their child to A&E if they:
Become pale, mottled or abnormally cold to touch
Pause in their breathing, have an irregular breathing pattern or grunt
Have severe breathing difficulties, while becoming agitated or unresponsive
Go blue around the lips
Have a seizure
Become extremely distressed, confused, lethargic or unresponsive
Develop a rash that does not disappear with pressure, like when pressed under a glass
Have testicular pain, especially teenagers