COVID-19 vaccine fast facts

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 Administration^1,2 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.

• 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

  • - 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

• 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%).

  • - 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.

• 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

  • - 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).

  • - 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

• Limitations: unknown efficacy in children and unknown duration of response.

Context

• Storage requirements^4,9,10: 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