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#294 Real World Evidence for COVID-19 Vaccines

What is the real-world effectiveness for currently available COVID-19 vaccines?

Similar to clinical trials, real world cohort and case-control studies find COVID-19 infections are reduced by >90% with two doses of mRNA vaccines. Single doses of either mRNA or AstraZeneca vaccine decreases infections by ~60% and hospitalizations by 70-80%. Vaccine effectiveness appears similar for variants of concern and are safe for pregnant women.

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  • From relatively short cohort/case-control studies or registries. Fully vaccinated defined as 7- or 14-days post-second dose.
  • Israel national vaccination (Pfizer) program of 6.5 million adults ≥16 years old.1 New COVID-19 cases in the program’s initial 10 weeks was compared to vaccine status. Full vaccination decreased risk of:
    • All COVID-19 infections: By 97%.
    • Hospitalizations and deaths: By 98% and 99% respectively.
    • Limitations: The same individuals contributed time to unvaccinated, partially vaccinated and fully vaccinated calculations.
  • United Kingdom case-control study, persons ≥70 years with COVID-19 (n=44,590) linked to vaccine status.2 Single dose of either Pfizer or AstraZeneca reduced:
    • Symptomatic infections: ~60% (~1 month after either vaccine).
    • Hospitalizations: 80% (either vaccine).
    • Death: ~85% [Pfizer (AstraZeneca death rates not reported)].
  • Ontario four-month case-control study, adults ≥16 years:3
    • Single-dose (Pfizer or Moderna) reduced:
      • Symptomatic infection: 60%.
      • Hospitalization or death: 70%.
    • Two-doses reduced:
      • Symptomatic infection: 91%.
      • Hospitalization or death: 98%.
  • Findings similar to clinical trials.4
  • Variants of Concern (VOC):
    • Two doses of Pfizer or AstraZeneca reduces symptomatic delta variant infections or hospitalizations similar to non-VOC infections.5
    • Pfizer or Moderna vaccination reduces symptomatic infection or hospitalizations in four current VOC (alpha, beta/gamma, delta) similar to non-VOC.6
      • Two doses are better than one.6
  • Safety in Pregnancy:
    • 35,691 pregnant women received Pfizer or Moderna vaccine (29% 1st trimester, 43% second trimester, 26% third trimester):7
      • Adverse pregnancy outcomes with vaccine same as baseline risk.7
    • Babies born to pregnant women with COVID-19 are twice as likely to develop severe perinatal morbidity and mortality.8
    • Pregnant women with COVID-19 have 50% greater risk of maternal morbidity or mortality.8
  • Pregnant women should be offered COVID-19 vaccine.9
  • Recommendations for vaccinated individuals available: Canada or United States.10,11

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  • Michael R Kolber BSc MD CCFP MSc
  • Paul Fritsch MD CCFP
  • Jennifer Young MD CCFP
  • Nicolas Dugré PharmD MSc BCPAC
  • Alexander Singer MB BAO BCh CCFP
  • Tony Nickonchuk BScPharm

1. Haas EJ, Angulo FJ, McLaughlin JM, et al. Lancet. 2021; Published Online May 5, 2021. S0140-6736(21)00947-8

2. Bernal JL, Andrews N, Gower C, et al. BMJ. 2021;373: n1088.

3. Chung H, Nasreen S, Sundaram ME, et al. MedRxiv preprint May 24, 2021; doi:;

4. Kolber MR, Fritsch P, Price M, et al. Can Fam Physician. 2021; 67:185-6.

5. Stowe J, Andrews N, Gower C, et al. Effectiveness of COVID-19 vaccines against hospital admission with the Delta (B.1.617.2) variant. Available at: Accessed June 29, 2021

6. Nasreen S, He S, Chung H, et al. MedRxiv preprint doi:; July 3, 2021.

7. Shimabukuro TT, Kim SY, Myers TR, et al. N Engl J Med. 2021; 384:2273-82.

8. Villar J, Ariff S, Gunier RB, et al. JAMA Pediatr. doi:10.1001/jamapediatrics.2021.1050

9. Poliquin V, Castillo E, Boucoiran I, et al. Society of Obstetrics and Gynecology. Statement of COVID-19 Vaccination in Pregnancy. Available at: Accessed June 8, 2021

10. Centre for Disease Control (CDC): Choosing Safer Activities. Available at: Accessed June 1, 2021

11. Public Health Agency of Canada (PHAC). Vaccinated Against COVID-19: What does it mean to me? Available at: Accessed June 27, 2021.

Authors do not have any conflicts of interest to declare.

Les auteurs n’ont aucun conflit d’intérêts à déclarer.