Association Between COVID-19 Vaccine Doses and Neurosensory Symptoms Among COVID-19-Positive Patients: A Retrospective Cross-Sectional Study.

BACKGROUND

Ageusia and anosmia are common manifestations of COVID-19. This study examined whether their frequency among infected patients was associated with the recorded number of Pfizer-BioNTech vaccine doses; it was not designed to estimate causality or vaccine effectiveness.

METHODS

We conducted a retrospective cross-sectional analysis of 5,348 COVID-19-positive patients over five years of age followed by the San Miguelito Health Region, Panama, from July 7, 2021, through November 2, 2022. Unvaccinated patients and vaccinated patients whose recorded doses were exclusively Pfizer-BioNTech were included. Separate logistic regression models estimated associations between vaccine dose category (zero, one, two, or three to four doses) and self-reported ageusia and anosmia, with two doses as the reference. A post hoc sensitivity analysis additionally adjusted for swab month.

RESULTS

Ageusia was reported by 507 patients (9.48%), and anosmia by 584 patients (10.92%). In the primary adjusted models, compared with two doses, adjusted odds ratios (aORs) for zero, one, and three to four doses were 1.87 (95% confidence interval (CI) 1.48-2.38), 2.68 (95% CI 1.99-3.60), and 0.26 (95% CI 0.18-0.36), respectively, for ageusia, and 1.82 (95% CI 1.46-2.27), 2.53 (95% CI 1.91-3.35), and 0.18 (95% CI 0.12-0.25), respectively, for anosmia. After categorical adjustment for swab month, all six dose-category estimates were attenuated, and none remained statistically significant.

CONCLUSIONS

Primary models identified strong associations between recorded vaccine dose category and self-reported ageusia and anosmia among infected patients, but these associations did not persist after adjustment for swab month. The results are compatible with substantial confounding by epidemic period and should not be interpreted as causal effects or estimates of vaccine effectiveness.