Clinical question
What are the benefits and risks of 3 coronavirus disease 2019 (COVID-19) vaccines?
Bottom line
Interim results (2 large RCTs) show the relative efficacy of the Pfizer-BioNTech and Moderna vaccines (about 95%) and the AstraZeneca-Oxford vaccine (about 70%) in preventing COVID-19. Absolute benefits will vary with baseline risk and time: if the annual risk of developing COVID-19 is 20%, then the vaccine would decrease the risk to 1% (6% with the AstraZeneca-Oxford vaccine). These vaccines appear safe and might decrease the likelihood of severe COVID-19. Ongoing studies should provide further details.
Evidence
Interim results are from US Food and Drug Administration1,2 or peer-reviewed publications (median follow-up of 2 months).3-5 The cases were symptomatic and had laboratory-confirmed COVID-19.5-7 Severe COVID-19 was defined as needing high-flow oxygen or intensive care unit admission.5-7 All relative risk reductions (RRRs) are statistically different.
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Pfizer-BioNTech: In 1 double-blind, multi-country RCT (N = 40 137; median age of 51),1,3,6 2 doses were given 21 days apart.1,3 The vaccine arm had 9 COVID-19 cases (1 severe) and the placebo arm had 169 cases (4 severe; RRR = 95%).3
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Unsolicited reported adverse events (AEs)1 included injection pain (11%), fatigue (6%), and myalgia or headache (5%). Solicited specific AEs yielded 5 to 10 times more responses (eg, fatigue reported in 34% to 59% of patients in the vaccine arm; 17% to 33% in the placebo arm).1,3 Incidence of serious adverse events (SAEs; about 0.5%) and incidence of deaths were similar between arms.1,3
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Moderna: In 1 double-blind RCT (N = 28 207; median age of 51),2,5,7 2 doses were given 28 days apart.2,5 The vaccine arm had 11 COVID-19 cases (0 severe) and the placebo arm had 185 cases (30 severe; RRR = 94%).
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Unsolicited reported AEs2 included headache (3%), fatigue (2%), lymphadenopathy (1.2%), and myalgia (1%). Solicited specific AEs yielded 5 to 20 times more responses (eg, headache was reported in 25% to 63% of patients in the vaccine arm; 18% to 29% in the placebo arm). Incidence of SAEs (0.6%) and incidence of deaths were similar between arms.
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AstraZeneca-Oxford: In 4 RCTs (N = 11 636) with multiple arms (including variable first dose and timing [4 to > 12 weeks] of second dose), 2 doses were given.4,8 The vaccine group had 30 COVID-19 cases (0 severe) and the placebo group had 101 cases (2 severe; RRR = 70%).4
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There was a lower RRR in the standard-dose regimen compared to the low-dose regimen (62% vs 90%). The low dose was given only to those between 18 and 55 years of age (roughly 90% health care workers).
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The vaccine group had 0.7% SAEs compared to 0.8% in the placebo group.4 There were 3 cases of transverse myelitis (2 cases with vaccine; 1 case with placebo), but were deemed unrelated to the vaccine.4 Overall mortality is similar between groups.4
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Limitations: unknown efficacy in children and unknown duration of response.
Context
Storage requirements4,9,10: Pfizer, -70°C; Moderna, -20°C; and AstraZeneca-Oxford, 2°C to 8°C.
Baseline risk of COVID-19 varies substantially with location and time, affecting potential absolute benefit (eg, if annual risk is 20%, Pfizer or Moderna vaccine decreases risk to 1% and AstraZeneca-Oxford to 6%).
Implementation
Preparation and administration requirements differ considerably.11-13 Anaphylaxis was a reported AE after Pfizer vaccine administration in about 1 per 90 000 doses, and in about 1 per 400 000 after Moderna vaccine administration; about 80% to 90% of anaphylactic patients had history of allergies or anaphylaxis.14,15
Tools for Practice articles in Canadian Family Physician are adapted from articles published on the Alberta College of Family Physicians (ACFP) website, summarizing medical evidence with a focus on topical issues and practice-modifying information. The ACFP summaries and the series in Canadian Family Physician are coordinated by Dr G. Michael Allan, and the summaries are co-authored by at least 1 practising family physician and are peer reviewed. Feedback is welcome and can be sent to toolsforpractice@cfpc.ca. Archived articles are available on the ACFP website: www.acfp.ca.
Footnotes
Competing interests
None declared
The opinions expressed in Tools for Practice articles are those of the authors and do not necessarily mirror the perspective and policy of the Alberta College of Family Physicians.
This article is eligible for Mainpro+ certified Self-Learning credits. To earn credits, go to www.cfp.ca and click on the Mainpro+ link.
La traduction en français de cet article se trouve à www.cfp.ca dans la table des matières du numéro de mars 2021 à la page e82.
References
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