Most people who lose their sense of smell while infected with Covid-19 recover within eight months, according to new research.
A study in France found 45% had fully regained it after four months - with another 53% reporting improvements.
But one in 50 said their symptoms had remained the same - or even worsened.
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Given the scale of the pandemic, hundreds of thousands of people could face long-term problems.
An inability to smell, known medically as anosmia, is now recognised as a core sign of coronavirus.
The NHS advises anyone who experiences it to isolate - together with their household - and be tested.
Corresponding author Dr Marion Renaud, of University Hospitals of Strasbourg, said: "Persistent Covid-19 related anosmia has an excellent prognosis with nearly complete recovery at one year.
"As clinicians manage an increasing number of people with post-Covid syndrome, data on long term outcomes are needed for informed prognostication and counselling."
Her team tracked 97 Covid patients who had suffered acute loss of smell for over a week for 12 months following diagnosis.
The men and women, mostly under 50, completed three surveys at four monthly interviews rating it.
They also had olfactory function assessed through psycho-physical tests using pen-like odour dispensing devices called 'Sniffin' Sticks'.
Of these participants, 51 underwent both subjective and objective olfactory test, and 46 only the former.
After subjective assessment 23 of the 51 patients (45%) reported full recovery, 27 (53%) partial recovery and one (2%) no recovery.
The psycho-physical testing showed 43 (84%) had normal smell - including 19 of 27 (70%) who self-evaluated as only partially recovered.
All those who self-reported normal return of smell were confirmed with objective testing.
The remaining eight (16%) with persistent subjective or objective loss of smell were followed up at eight months.
An additional six were found to have regained normal smell on objective testing.
At eight months, objective olfactory assessment confirmed full recovery in 49 of the 51 (96%).
Dr Renaud said two patients remained with loss of smell after a year, with "persistent abnormalities."
Among those who underwent subjective assessment alone, 13 of 46 patients (28%) reported satisfactory recovery at 4 months - seven with total and six with partial recovery.
The remaining 33 patients (72%) did so by 12 months - 32 with total and 14 with partial recovery.
Dr Renaud added: "Since the pandemic was declared in early 2020, Covid-19–related anosmia quickly emerged as atelltale sign of infection.
"However, the time course and reversibility of Covid-19–related olfactory disorders, which may persist and negatively affect patients' lives, require further study.
The study, published in JAMA Network Open, is based on data collected from June 2020 to March this year.
