During clinical trials for ABRYSVO, in persons 60 years of age and older, the most commonly reported adverse events included swelling, pain, and redness at the injection site, fatigue, headache, muscle and joint pain, nausea, vomiting diarrhea, and fever.
In the first month following vaccination, more people in the vaccine group reported severe adverse events. These severe adverse events included falls, sepsis, congestive obstructive pulmonary disease, and infections/infestations. Study investigators, however, reported that these adverse events were likely not related to vaccination.
Atrial fibrillation, a serious heart disorder, that may lead to complications such as stroke, heart attack, or heart failure, occurred at a higher rate among vaccine recipients than those who received the placebo. While clinical trial investigators reported that the vaccine was not responsible, the FDA has stated that they are continuing to investigate.
Two cases of Guillain Barre Syndrome (GBS), a rare neurological disorder that causes inflammation of the peripheral nerves with complications that can include temporary or chronic paralysis, including full body paralysis, and may lead to death, also occurred during the clinical trial, at a rate of approximately 1 in 9,000. Additionally, one clinical trial participant who received the experimental RSV vaccine experienced a delayed allergic reaction, with complications that included shortness of breath, chest pain, and loss of consciousness.
Pfizer’s clinical trials used a placebo solution containing ingredients that were similar to the vaccine, minus the RSV antigens, rather than using an inert saline placebo.
In clinical trials of the vaccine for use in pregnant women, individuals who received the vaccine experienced higher rates of injection site and systemic reactions than those who received the placebo. The most commonly reported systemic reactions included fatigue, headache, muscle and joint pain, nausea, vomiting, and diarrhea.
Severe or life-threatening adverse events occurring within one month of vaccination were higher among women who received the RSV vaccine, when compared to those who received the placebo (2.2 percent in the vaccine group versus 1.5 percent in the placebo group). Women who received the RSV vaccine were also more likely to experience a non-serious adverse event within one month of vaccination (11.2 percent versus 10. 8 percent).
Women who received the RSV vaccine were more likely to experience premature delivery of their infants when compared to those who received the placebo (5.6 percent versus 4.7 percent). Higher rates of pre-eclampsia and gestational hypertension were noted among vaccine recipients when compared to those who receive the placebo.
In the recommendation for the use the Pfizer RSV vaccine in pregnant women for the prevention of RSV illness in their newborn infants, the CDC’s Advisory Committee on Immunization Practices noted that:
“For the GRADE assessment of harms, results from the phase 2b and phase 3 trials were pooled¶¶ (9,16). The overall evidence certainty using GRADE criteria was rated as very low, driven by the uncertainty in the critical harm outcome of preterm birth (<37 weeks’ gestation).*** ACIP judged the benefits of maternal RSVpreF vaccination at 32–36 weeks’ gestation to outweigh the potential risks for preterm birth and hypertensive disorders of pregnancy.”
GRADE (Grading of Recommendations Assessment, Development and Evaluation) is an evidence-based framework used by the CDC’s ACIP to assess the type or quality of evidence about a vaccine’s expected health impacts and the balance of health benefits and risks, along with the values and preferences of persons affected, and health economic analyses.
According to the GRADE system used by the ACIP for evaluating evidence, very low certainty evidence means that confidence in the evidence is lacking and that The true effect is likely to be substantially different from the estimate of effect.
Pfizer’s clinical trial data also reported that 37.1 percent of infants whose mothers received the RSV vaccine experienced an adverse event within one month of birth, with 15.5 percent reported as serious, 4.5 percent as severe, and 1 percent as life-threatening. One woman who received the RSV vaccine died due to complications from post-partum hemorrhage and hypovolemic shock after delivery. Eighteen intrauterine deaths were also reported in clinical trials, with 10 occurring in the vaccine group and 8 in the vaccine group.
