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Are vaccine side-effects more common with Moderna or Pfizer?

Question: Social media friends were saying the Modern’s side effects are worse than Pfizer’s.  Is there a difference?

Answer: We talked about this recently (see Q&A of 3/23), and generally there are no major differences between type and severity of side effects between Pfizer and Moderna (J&J too).  Your question is timely though, because yesterday JAMA published a new study on this very topic, Reactogenicity Following Receipt of mRNA-Based COVID-19 Vaccines.  The authors analyzed data collected from mid-December through end-February from CDC’s V-Safe database, observing degree and type of reactogenicity (e.g. vaccine side effects) from days 0-7 after each vaccine dose for both Pfizer and Moderna.  They found that overall:

  • Real-world experiences are consistent with clinical trial results. “The frequency of reported reactions was generally consistent with results observed in clinical trials.”     
  • Moderna recipients are more likely to report side effects. “A greater percentage of participants who received the Moderna vaccine, compared with the Pfizer-BioNTech vaccine, reported reactogenicity; this pattern was more pronounced after the second dose.” (Table)   
  • Side effects are less commonly reported by those ages 65+. “Local and systemic reactions were less commonly reported by v-safe participants 65 years and older compared with those younger than 65 years ”  
  • Common side effects after the first dose include pain at the injection site, fatigue, headache, and muscle pain. The most frequently reported reactions after the first dose were “injection site pain (67.8%), fatigue (30.9%), headache (25.9%), and myalgia (19.4%).”   
  • Side effects after the second dose were more common and also included chills, fever, and joint pain. “Reactogenicity was substantially greater after the second dose for both vaccines.. including fatigue (53.9%), headache (46.7%), myalgia (44.0%), chills (31.3%), fever (29.5%), and joint pain (25.6%).”

Table. Reactions by Vaccine Type (from JAMA)