Side Effects of Mixing Vaccines against COVID-19 Infection among Saudi Population

Background: Mixing two different vaccines has been utilized to minimize the impact of any supply chain interruptions and to combat the COVID-19 pandemic in Saudi Arabia. We conducted this study to evaluate the side effects, if any, associated with the mixed vaccination approach. Methods: An online survey study was administered among COVID-19 vaccine recipients in Saudi Arabia. Symptoms post vaccination were assessed in 311 vaccinated participants with two matched doses of either Oxford-AstraZeneca or Pfizer-BioNTech vaccines, or two mixed doses, respectively. Results: After the second dose, around 31% of the matched vaccine group reported no symptoms, while only 6% of the mixed vaccine group reported no symptoms. Most of the side effects after the second dose associated with matched vaccines were injection site pain (46%), while the mixed vaccines group reported significantly more symptoms compared with the matched vaccine group, which included fever (41%), fatigue (66%), muscle pain (44%), chills (17%) and injection site pain (60%). Conclusion: The data suggest the overall safety of the mixed vaccination protocol; however, it might be associated with side effects such as fever, fatigue, muscle pain, chills, and injection site pain. Further studies with a larger cohort size could shed more light on this aspect, which would be imperative for deciding to utilize a mixed vaccination approach.