BACKGROUND AND PURPOSE:

• In phase 3 clinical trials of the Pfizer-BioNTech vaccine, injection-site pain (71 to 83%), fatigue (34 to 47%), and headache (25 to 42%) were commonly seen
• Menni et al. (The Lancet Infectious Diseases, 2021) investigate the safety and effectiveness of the Pfizer and AstraZeneca vaccines in a UK community setting

METHODS:

• Prospective observational study
• Data source
  • COVID Symptom Study app data
  • Between Dec 8 through March 10, 2021
• Population
  • General UK population 
• Exposure
  • One or two doses of the Pfizer -BioNTech vaccine
  • One dose of the AstraZeneca vaccine
  • Unvaccinated controls
• Study design
  • All analyses were adjusted by
    • Age (≤55 years vs >55 years)
    • Sex
    • Health-care worker status (binary variable)
    • Obesity (BMI <30 kg/m2 vs ≥30 kg/m2)
    • Comorbidities (binary variable, with or without comorbidities)
• Primary outcome
  • Proportion and probability of self-reported systemic and local side effects within 8 days of vaccination
• Secondary outcome
  • SARS-CoV-2 infection rates in vaccinated individuals

RESULTS:

• 627,383 vaccinated individuals
  • At least one dose of Pfizer-BioNTech: 282,103 individuals | Two doses of Pfizer-BioNTech: 28,207 individuals
  • One dose of AstraZeneca: 345,280 individuals

Systemic Side Effects

• Report rates of systemic side effects after vaccination
  • After first dose of Pfizer-BioNTech: 13.5% | After second dose of Pfizer-BioNTech: 22.0%
  • After first dose of AstraZeneca: 33.7%
• Most common systemic side effects
  • Fatigue and headache
  • Usually within first 24 hours after vaccination | Lasted a mean of 1.01 days
• Systemic side effects were more common among those with a history of previous SARS-CoV-2 infection
  • After first dose of Pfizer-BioNTech: 2.9 times more likely
  • After first dose of AstraZeneca: 1.6 times more likely
• Adverse systemic events were more common in
  • Women vs men: 16.2% vs 9.3% after first dose of Pfizer-BioNTech (OR 1.89 [95% CI, 1.85 to 1.94]; p<0·0001) and similarly after first dose of AstraZeneca
  • ≤55 years vs >55 years: 20.7% vs 10.6% after first dose of Pfizer-BioNTech (OR 2.19 [95% CI, 2.14 to 2.24]; p<0.0001) and similarly after first dose of AstraZeneca
  • Similar pattern in women and younger individuals were also noted for local side effects

Local Side Effects

• Most common local side effects
  • Tenderness and local pain around the injection site
  • Usually on the day after injection | Lasted a mean of 1.02 days
• Local side effects after vaccination
  • After first dose of Pfizer-BioNTech: 71.9% | After second dose of Pfizer-BioNTech: 68.5%
  • After first dose of AstraZeneca: 58.7%
• Local side effects were also higher in individuals previously infected with SARS-CoV-2
  • After first dose of Pfizer-BioNTech: 1.2 times more likely to experience side effects
  • After first dose of AstraZeneca: 1.4 times more likely

Vaccine Effectiveness

• SARS-CoV-2 positive tests
  • Vaccinated: 3% (3106 infections per 103,622 vaccinated)
  • Unvaccinated: 11% (50,340 infections per 464,356 unvaccinated)
• Significant reductions in infection risk were seen starting at 12 days after the first dose and increased over time
  • At 21 to 44 days
    • Pfizer-BioNTech: 69% (95% CI 66 to 72)
    • AstraZeneca: 60% (95% CI 49 to 68)
  • At 45 to 59 days
    • Pfizer-BioNTech: 72% (95% CI 63 to 79)

CONCLUSION:

• Systematic and local side effects with Pfizer and AstraZeneca COVID-19 vaccination were more common in women, individuals ≤55 years, and those with previous COVID-19 infection
• A reduction in infection risk was observed starting 12 days after the first dose for both vaccines
• The authors conclude

Localised and systemic side effects after vaccination are less common in a real-world community setting than reported in phase 3 trials, mostly minor in severity, and self-limiting

Our data will enable prediction of side-effects based on age, sex, and past COVID-19 status to help update guidance to health professionals to reassure the population about the safety of vaccines

Learn More – Primary Sources:

Vaccine side-effects and SARS-CoV-2 infection after vaccination in users of the COVID Symptom Study app in the UK: a prospective observational study