# Lichen Planus Following COVID‐19 Infection and Vaccination. Matched Case–Control Study

## TL;DR

This study finds a strong link between new cases of lichen planus and recent COVID-19 infection or vaccination.

## Contribution

The study provides the first matched case–control evidence linking LP to recent COVID-19-related events.

## Key findings

- Conditional and unconditional odds ratios showed a significant association between LP and recent COVID-19 events.
- Subgroup analysis confirmed that symptomatic infection is strongly linked to LP.
- Sensitivity analysis supported the robustness of the primary findings.

## Abstract

New‐onset lichen planus (LP) development following COVID‐19 infection/vaccination is reported. Since case series cannot be used to study exposure–outcome associations, we designed this matched case–control study to investigate whether COVID‐19‐related events and de novo LP are associated.

Patients with histologically confirmed LP, newly diagnosed at the National Research Center of Dermato‐Venereology of Moscow (September 2020–December 2022), were considered. Sex/age/ethnicity‐matched controls attending the same Center in the same period for consultations on conditions unrelated to LP were selected. Cases/controls with known LP trigger factors were excluded. COVID‐19‐related events were: symptomatic COVID‐19 (PCR‐confirmed), and COVID‐19 vaccination (viral vector vaccine) occurred ≤ 1 month before the visit at the Center. The association between COVID‐19‐related events and LP was assessed with conditional (Mantel–Haenszel method) and unconditional (logistic regression analysis adjusted for sex, age, and smoking) analyses. Subgroup analysis, with COVID‐19 infection and vaccination treated separately, and sensitivity analysis on another group of patients with suspected LP, not confirmed histologically, were also made.

Fifty‐five case–control pairs were considered. Mean age (51 years), sex (56.4% females) and ethnicity (100% whites) distributions were the same in both groups. Conditional and unconditional odds ratios resulted 7.50 (95% Confidence Interval –95CI, 1.72–32.80), 4.45 (95CI, 1.63–12.15), respectively (p < 0.05). Subgroup analysis confirmed the association between symptomatic infection and LP, while sensitivity analysis corroborated the results of the primary analysis.

This observational study, reporting a strong significant association between COVID‐19 infection/vaccination and de‐novo LP, suggests that COVID‐19‐related events, especially infection, could act as LP trigger factors.