Rare adverse events after COVID-19 vaccination among Swedish older adults-evidence from a nationwide register-based study

COVID-19 vaccinations have saved millions of lives, particularly among older adults. Rare potential adverse events have been reported in case reports, but risks among older adults remain unclear. This study assessed risks of selected potential adverse events in this population.

We included more than 2 million Swedish adults ≥65y in a nationwide register-based cohort. Post-vaccination risks were assessed for herpes zoster (HZ), encephalitis, myelitis and encephalomyelitis, multiple sclerosis (MS), myasthenia gravis, cranial nerve palsy, sudden sensorineural hearing loss (SSNHL), postinfectious arthritis and polymyalgia rheumatica (PMR) in several risk windows (1-30, 31-60, and 61-180 days) after each vaccine dose. Hazard ratios (HRs) with 95% confidence intervals (95%CIs) compared with unvaccinated were estimated by Cox regression adjusted for potential confounders. Sensitivity analyses included adding primary health care (PHC) visits, and applying analysis-specific 5-year disease-free wash-out periods.

No increased HRs were observed for most outcomes. SSNHL showed increased HRs within 180 days after each dose [1.60 (95%CI 1.15-2.24); 1.43 (1.03-1.99); 1.61 (1.05-2.46) for dose 1, 2 and 3], with similar estimates across all three risk windows. Increased HRs were also seen for PMR after dose 2 [1.14 (1.04-1.24)] and dose 3 [1.16 (1.03-1.30)], with higher HRs during later time windows. HZ showed increased HRs in the sensitivity analysis with PHC visits, [1.19 (1.07-1.31); 1.31 (1.19-1.43); 1.42 (1.26-1.60) for dose 1, 2 and 3]. MS showed reduced risk after dose 3 in the sensitivity analysis with longer wash-out (targeting incident MS), but not in the main analysis (potential relapses included).

COVID-19 vaccines are generally safe in older adults, with very low incidence of the potential rare adverse events assessed. Slightly increased relative risks for SSNHL, PMR and HZ were observed, but these findings do not alter the overall benefit-risk profile of COVID-19 vaccination in older adults.