(256) Risk of Rhabdomyolysis After Influenza Vaccination: A Case-Centered Analysis

Sunday, August 28, 2022

8:00 AM – 1:45 PM CEST

Location: Hall C

Publication Number: 1301

Presenting Author(s)

Che-Yu Chen
– NCKU Institute of Clinical Pharmacy and Pharmaceutical Sciences, Tainan, Tainan, Taiwan

Co-Author(s)

Edward Lai, PhD
– Associate Professor, National Cheng Kung University, National Cheng Kung University, Tainan City, Tainan, Taiwan (Republic of China)
Wan-Ting Huang
– National Taiwan University Children's Hospital, Taipei, Taiwan (Republic of China)
Miyuki Hsing-Chun Hsieh
– NCKU Institute of Clinical Pharmacy and Pharmaceutical Sciences, Chiayi City, Taiwan

Background: Taiwan’s seasonal influenza mass vaccination program was initiated in 1998. This annual program starts in October, targeting individuals at high risk for negative outcomes from influenza infection. The priority groups were expanded to include individuals aged 50+ years in 2016. Few case reports of acute rhabdomyolysis following influenza vaccines in the elderly have raised concerns that the vaccines may rarely cause rhabdomyolysis.

Objectives: To evaluate the risk of rhabdomyolysis after influenza vaccination by using case-centered design.

Methods: We included individuals enrolled in Taiwan's National Health Insurance Research Database (NHIRD) from 2016 to 2018. We identified patients aged 50+ years with all first-ever diagnoses of rhabdomyolysis (ICD-10 code: M62.82) and defined a case as patient who received at least one influenza vaccine within 365 days before the diagnosis. We defined the date of diagnosis as the index date for the case, and selected risk interval of 0 to 28 days. Each case patient was matched by sex and age (+/-2 years) to the entire NHIRD population who, as of the same index date, received influenza vaccine within the previous 365 days. The observed odds of cases vaccinated inside (0 to 28 days) vs outside (29 to 365 days) the risk interval was compared with the expected odds derived from the matched population vaccinated inside vs outside the risk interval. The odds ratio (OR) was estimated by stratified logistic regression. Different length of risk intervals, including 0 to 7 and 0 to 14 days before the index date, were examined to evaluate the robustness of the results.

Results: We identified 2,527 cases of rhabdomyolysis with a mean age of 71.7 years (SD, 11.4) (67% male) and 5,632,174 vaccinated enrollees of the same age and sex. The median time from vaccination to onset of rhabdomyolysis was 28 weeks (IQR, 14-40). Compared to the matched population, we found the OR of receiving influenza vaccine during the risk interval of 0 to 28 days was 0.65 (95% CI, 0.52–0.82) for the cases. The decrease in ORs remained consistent for the various risk intervals of 0 to 7 days (OR 0.45, 95% CI 0.29–0.68) and 0 to 14 days (OR 0.62, 95% CI 0.47–0.83).

Conclusions: Risk of rhabdomyolysis was not increased during the 28 days after influenza vaccination in the elderly in Taiwan. Instead, a reduced risk was observed and might be explained by the healthy vaccinee effect, or the protection of influenza-induced rhabdomyolysis from vaccination.