Adverse reactions to vaccination are closely monitored in the so-called pharmacovigilance system, both during the clinical trial and in the post-licensure phase. It is possible to document what specific problems may occur with a particular vaccine.
Pfizer launched a phase III clinical trial in July. In previous studies, some patients experienced common side effects such as injection-site reactions (pain, rash, muscle pain), headaches, nausea and fever. These side effects usually resolved within two days. An FDA report published in December stated that the most common solicited adverse reactions were injection site reactions (84.1%), fatigue (62.9%), headache (55.1%), muscle pain (38.3%), chills ( 31.9%), joint pain (23.6%), fever (14.2%). The FDA reported that four patients who received the vaccine developed facial paralysis.
In phase III clinical trial, also launched in July by Moderna, adverse reactions were monitored. In previous studies, almost half of the patients experienced common side effects such as injection-site reactions (pain, rash, muscle pain), headaches, nausea and fever after the second dose. These side effects usually resolved within two days. In an FDA report published in December, the most common side effects were injection site pain (91.6% of patients), fatigue (68.5%), headache (63.0%), muscle pain (59.6%), joint pain (44.8%) and chills (43.4%). Three patients developed facial nerve palsy, a sudden and usually temporary weakening or paralysis of the facial muscles. In several patients with dermal fillers, some swelling occurred after receiving the first dose of the vaccine. They were treated with antihistamines and steroids.
Twenty-nine people in the United States had anaphylactic reactions to either Pfizer or Moderna (for example, in Israel, there were anaphylactic reactions in approximately 2 cases per million vaccinated doses.) Most were treated with epinephrine (the drug in EpiPens) and none of them died. From now on, the CDC recommends taking precautions for patients who have a history of anaphylactic reaction to any vaccination but may continue to be vaccinated with precautionary measures. Patients are now monitored for 15-30 minutes after vaccination to observe signs of anaphylaxis.
Moderna has announced that it will start testing its vaccine in children and adolescents that are believed to have stronger immune responses, leading to more intense side effects such as fever and pain.
The original author of the text: prof. MUDr. Roman Prymula, CSc., PhD.
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