(35) Risk of Hip Fracture in the Elderly Following Covid-19 Vaccination in Hong Kong: A Self-Controlled Case Series Study

The effectiveness of COVID-19 vaccines has been validated in real-world settings. However, many people are still hesitant to get COVID-19 vaccines in concerns about the safety and side effects. Although studies have shown that COVID-19 vaccines are generally safe, common side effects, like fatigue, muscle and joint pain, and headache, may increase the risk of falls and hip fractures in the elderly, which is also the most susceptible group to COVID-19. The relationship between COVID-19 vaccination and hip fractures has never been studied before.

In this study, we investigated the association of CoronaVac and BNT162b2 vaccines with incident hip fractures among older Hong Kong residents using a self-controlled case series (SCCS) study design. The vaccination data were curated by the Department of Health of the Government of Hong Kong and linked to the clinical data from the electronic healthcare database at the individual level. From February 23, 2021, to January 31, 2022, people admitted to the hospital (inpatients, outpatients, or emergency) with the outcome of interest were included. The outcome of interest was hip fractures defined by the International Classification of Diseases, Ninth Revision codes (ICD-9) 820. We excluded those aged < 65, had a medical history of Paget’s disease of bone, osteogenesis imperfecta, and/or metastatic cancer, and/or died during the study period. The exposures were the first or second dose of CoronaVac or BNT162b2 vaccines in the study period. We defined the exposure risk intervals as 1–7, 8–14, 15–21 and 22–28 days after each exposure date, assuming that the adverse events are not related to exposure later than 28 days postexposure. Fixed-effects Poisson regression models with seasonal effects adjusted, conditioned on the individual, were used to estimate incidence rate ratios (IRR) and 95% confidence intervals (95% CI), comparing the hip fracture rate after vaccination to the baseline rate.

4,252 cases were included in the SCCS analysis, among which 3,088 were unvaccinated, 1,164 received at least one dose of COVID-19 vaccines (827 CoronaVac; 337 BNT162b2), and 754 received two doses of vaccines (498 CoronaVac; 256 BNT162b2). Among CoronaVac recipients, we identified 72 and 41 cases within 28 days following the first and second doses and the respective 20 and 29 cases among BNT162b2 recipients. The risk of hip fracture increased in 1–7 days after the first dose of CoronaVac (IRR, 1.76; 95% CI: 1.14, 2.71) and 1–7 days after the second dose of BNT162b2 (IRR, 2.25; 95% CI: 1.20, 4.24). No significant association was observed in other risk periods.

To our knowledge, it is the first study to investigate the association between hip fractures and COVID-19 vaccines. The increased risk of hip fracture after vaccination may be primarily due to an increased risk of falls. Fatigue and headache, two common side effects of COVID-19 vaccines, have been shown to be associated with an increased risk of falls. After receiving COVID-19 vaccines, the elderly should exercise caution to avoid falls and related injuries if side effects occur.