Study examines the safety of COVID-19 XBB.1.5 vaccines in older adults

XBB.1.5-containing vaccines were recommended as a fifth COVID-19 vaccine dose forindividuals aged 65 years or older in Denmark, beginning October 1, 2023. However, little data are available to support the safety of XBB.1.5 COVID-19 vaccines.To explore vaccine safety, Danish investigators examined the association between XBB.1.5-containing vaccines administered as a fifth COVID-19 vaccine dose and the risk of 28 adverse events. Using a nationwide healthcare registry, the study included all individuals in Denmark 65 years of age or older who had already received four COVID-19 vaccine doses. Patients were followed for 28 adverse events, which were adapted from prioritized lists of adverse events of special interest to COVID-19 vaccines. Each outcome was studied separately and identified as any first hospital contact where an outcome diagnosis was recorded. The 28 adverse events studied were as follows: ischemic cardiac event, any cerebrovascular event, cerebral infarction only (including transient ischemic attack), arterial thromboembolism, deep vein thrombosis, pulmonary embolism, myocarditis, pericarditis, cerebral venous thrombosis, thrombocytopenia and coagulative disorders, Guillain-Barré syndrome, Bell palsy, transverse myelitis, encephalomyelitis or encephalitis, narcolepsy, appendicitis, aseptic arthritis, type 1 diabetes, subacute thyroiditis, heart failure, arrhythmia, acute liver failure, acute kidney failure, acute pancreatitis, erythema multiforme, seizure, arterial aneurysm and uveitis.Individuals were followed from day 43 after the fourth dose (days 29–42 considered a buffer period). Outcome rates within the risk period of 28 days following XBB.1.5-containing vaccine administration as a fifth dose were compared with reference period rates from day 43 onwards after a fourth or fifth dose. The risk and reference period outcome rates were compared by incidence rate ratios, adjusted for sex, age, region of residence, high risk of severe COVID-19, healthcare worker, calendar time and number of comorbidities. Results showed the following:The study included 1,076,531 individuals (mean age, 74.7 years; 53.8% female). 902,803 individuals received an XBB.1.5-containing vaccine as a fifth dose.Receipt of an XBB.1.5-containing vaccine was not associated with a statistically significant increased rate of hospital contacts for any of the 28 different adverse events within 28 days after vaccination compared with the reference period rates.For example, the incidence rate ratio was 0.96 (95% confidence interval [CI], 0.87–1.07) for an ischemic cardiac event, 0.87 (95% CI, 0.79–0.96) for a cerebral infarction and 0.60 (95% CI, 0.14–2.66) for myocarditis. Some outcomes were very rare during follow-up (e.g., cerebral venous thrombosis), resulting in lower statistical precision; however, for 18 of the 28 adverse events examined, the upper bound of the confidence interval was inconsistent with moderate to large increases in relative risk of 1.4 or greater.The authors conclude that in this nationwide cohort of more than one million older adults, no increased risk of 28 adverse events was observed following vaccination with a monovalent XBB.1.5-containing vaccine given as a fifth COVID-19 vaccine dose.Reference:1. Andersson NW, Thiesson EM, Hviid A. Adverse events after XBB.1.5-containing COVID-19 mRNA vaccines. JAMA 2024. Published online February 26, 2024. (accessed February 29, 2024).

Study examines the safety of COVID-19 XBB.1.5 vaccines in older adults

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