In pre-licensing clinical trials, the most frequently reported side effect was pain at the injection site. Within four days of receipt of the vaccine, the most commonly reported systemic adverse events included fatigue, myalgia, headache, arthralgia, and fever. Severe systemic adverse events occurred in 3.3 percent of individuals who received the vaccine.
One case of Guillain-Barre Syndrome (GBS) was reported among the 15,400 clinical trial participants. There was also a higher rate of vaccine recipients who experienced atrial fibrillation in comparison to those who received the placebo. Additional serious side effects included Bell’s Palsy, gout, pancytopenia, Graves’ Disease, and aggravation of psoriasis.
GSK also reported that in one clinical trial, Study 007, which studied the use of the experimental RSV shot when given at the same time as the quadrivalent influenza vaccine, of the 442 participants, two cases of Acute Disseminating Encephalomyelitis (ADEM) had occurred, with one case resulting in death.
Clinical trials of an experimental RSV vaccine without an adjuvant that contained the same RSVPreF3 antigen as AREXVY conducted in pregnant women found higher rates of pre-term births when compared to those who received a placebo containing sucrose reconstituted with saline (6.81 percent versus 4.95 percent). GSK halted all clinical trials of the vaccine in pregnant women in February 2022 due to an undisclosed safety signal that occurred during the clinical trials.
