Patients randomized into the less than 12 months PRP arm will receive 3 doses of topical PRP each month apart and their sense of smell will be assessed during each visit followed by a monthly remote assessment of smell from home.

Patients randomized into the less than 12 months placebo arm will receive saline topically every month apart and their sense of smell will be assessed during each visit followed by a monthly remote assessment of smell from home.

Patients randomized into more than 12 months PRP arm will receive 3 doses of topical PRP each month apart and their sense of smell will be assessed during each visit followed by a monthly remote assessment of smell from home.

Patients randomized into the less than 12 months placebo arm will receive saline topically every month apart and their sense of smell will be assessed during each visit followed by a monthly remote assessment of smell from home.

Platelet-rich plasma will be placed on the olfactory epithelium topically.

Investigate the effect of topical PRP on olfaction via smell identification testing using a brief smell identification test (B-SIT). The change in smell identification with PRP or placebo over time will be assessed using B-SIT, a validated 12-odorant scratch-and-sniff questionnaire. The maximum possible score is 12, and the minimum score is 0. A score greater than or equal to 8 is considered normal olfaction, while a score lesser than three should raise a suspicion of malingering. Hence a higher score implies better outcomes.

Investigate the effect of topical PRP on olfaction via smell identification testing using SCENTinel smell test.

The SCENTinel test assesses for odor identification and the threshold of identification. Every month the participant is provided with one SCENTinel card - a QR-coded Lift'n'smell card containing a single target odorant and two blank odorants. The QR code leads to an electronic questionnaire the subject must fill out. Results with less than 40% Odor threshold are considered olfactory dysfunction. Hence a higher score implies better outcomes. The change in participants' threshold of identification will be assessed monthly over a year.

Investigate and compare the effect of topical PRP vs saline on quality of life participants using the Questionnaire of olfactory disorders negative statements only (QODNS) scale.

QODNS scale has 17 questions with each question scored between 0 to 3. The maximum score is 51 and the minimum score is 0 with higher scores being inversely related to the quality of life ie a higher score implies worse quality of life. The change in quality of life will be assessed monthly over one year.

Investigate the natural course of post-COVID / post-viral olfactory dysfunction in patients treated with placebo for the study by comparing the smell test.