EFFECT OF FULL VACCINATION AND POST-COVID OLFACTORY DYSFUNCTION IN RECOVERED COVID-19 PATIENT. A RETROSPECTIVE LONGITUDINAL STUDY WITH PROPENSITY MATCHING
Authors: Herman Bumi , Viwattanakulvanid Pramon , Dzulhadj Azhar , Oo Aye Chan , Patricia Karina , Pongpanich Sathirakorn 
Published: January 2022

Background

Symptoms after COVID-19 infection affect the quality of life of its survivor especially to the special senses including olfactory function. It is important to prevent the disability at an earlier stage. Vaccination as key prevention has been proven to be effective in reducing symptomatic disease and severity. However, the effects of vaccination on post COVID symptoms have not been evaluated. This study aimed to evaluate the possible protection of full vaccination and the occurrence of post-COVID olfactory dysfunction, specifically anosmia and hyposmia in patients who were diagnosed with COVID19.

Method

A longitudinal analysis using the retrospective cohort of the Indonesian patient-based Post-COVID survey collected from July 2021 until December 2021, involving COVID-19 Patients confirmed by RT-PCR and/or Antigen test. Variables including demography, comorbidities, health behavior, type of vaccine, symptoms, and treatment were collected through an online questionnaire based on the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS). Participants were matched (1:1) using propensity matching score into two exposure statuses, infected 1)>14 days of full vaccination and 2)<14 days or incomplete or unvaccinated. The olfactory dysfunction was assessed two weeks and four weeks after negative conversion with PCR using a self-measured olfactory questionnaire (MOQ). The Generalized Estimating Equation (GEE) was performed to assess the effect of full vaccination on post-COVID olfactory dysfunction. The Receiver Operating Characteristic determined the sensitivity and specificity of the cutoff value of the days from fully vaccinated to diagnosis and the olfactory dysfunction.

Results

A total of 442 participants were extracted from the cohort and inoculated with the inactivated viral vaccine (99.5%). The prevalence of olfactory dysfunction in two weeks was 9.95% and 5.43% after four weeks. Adjusted by other variables, people who were infected >14 days after being fully vaccinated had a 69% (adjusted OR 0.31 95% CI 0.102-0.941) probability of developing olfactory dysfunction. Longer days of fully vaccinated to infection associated with increased risk (adjusted OR 1.012 95% CI 1.002-1.022 p-value 0.015). A cut-off of 88 days of full vaccination-to-diagnosis duration has Area Under Curve (AUC) of 0.693 (p=0.002), the sensitivity of 73.9%, and specificity of 63.3% in differentiating the olfactory dysfunction event in two weeks after COVID with a crude odds ratio of 4.852 (95% CI 1.831-12.855 p=0.001)

Conclusion

After 14 days of full vaccination, the protective effect could reduce the chance of post-COVID olfactory dysfunction although a longer full vaccination-to-diagnosis duration increases the risk. It is important to consider a booster shot starting from 89 days after the last dose in those who received the inactivated viral regimen.