The ChAdOx1 nCoV-19 (AZD1222) vaccine is effective against symptomatic COVID-19 and has an acceptable safety profile.

A study was carried to explore the efficacy and safety of the ChAdOx1 nCoV-19 vaccine in a pooled interim assessment of 4 ongoing clinical trials.

The study incorporated data from four ongoing blinded, randomized, controlled trials: (i) COV001 (phase ½, United Kingdom), (ii) COV002 (phase II/III; United Kingdom), (iii) COV003 (phase III; Brazil), and (iv) COV005 (phase I/II; South Africa). Individuals (aged 18 years and older) were randomized to either the AZD1222 vaccine group or the control (meningococcal group A, C, W, and Y conjugate vaccine or saline) group. Subjects in the AZD1222 group were given two doses containing 5×10¹⁰ viral particles (standard dose; SD/SD); a subset in the United Kingdom trial that was given a half dose as their first dose (low dose) and a standard dose as their second dose (LD/SD).

The primary endpoint was symptomatic COVID-19 in seronegative individuals with a nucleic acid amplification test-positive swab more than 14 days after the second dosage of vaccine. Subjects were examined based on therapy administered, with data cutoff on 4 November 2020. The efficacy of AZD1222 was estimated as 1−relative risk derived from a robust Poisson regression model adjusted for age. Overall, 23,848 subjects were recruited and 11,636 subjects were incorporated in the interim primary efficacy analysis.

The overall vaccine efficacy, efficacy in subjects who were given two standard doses, and in subjects who were given a low dose followed by a standard dose is shown in the following table:

From 21 days following the initial dose, there were ten subjects hospitalized due to coronavirus, all in the control group; two patients were found to suffer from severe coronavirus disease, including one mortality. There were 74341 person-months of safety follow-up (median 3·4 months): 175 noxious effects occurred in 168 subjects, 91 in the control group, and 84 events in the AZD1222 arm. Three events were classified as possibly linked to a vaccine: one in the ChAdOx1 nCoV-19 arm, one in the control arm, and one in a subject who remains masked to the cohort distribution. 

ChAdOx1 nCoV-19 has a good safety profile and is effective against symptomatic COVID-19, with no hospitalizations or severe cases noted in the ChAdOx1 nCoV-19 recipients.