A new NEJM study has shown that the Oxford/AstraZeneca COVID-19 vaccine was safe and efficacious in preventing symptomatic and severe Covid-19 across all age groups including in older adults.

The double-blind, randomized, placebo-controlled, phase 3 clinical trial included a total of 32,451 persons at high risk for exposure to SARS-CoV-2 infection as well as those at risk of severe Covid-19.

Researchers examined the safety, vaccine efficacy, and immunogenicity of two doses of the Oxford/AstraZeneca COVID-19 vaccine (AZD1222) vis-à-vis placebo in preventing the onset of symptomatic and severe Covid-19. The trial was conducted at 88 sites in the United States, Chile and Peru.

21,635 participants were randomized to the Oxford/AstraZeneca COVID-19 vaccine group (two doses), while 10,816 participants were administered the placebo. The onset of the first symptom (confirmed by RT PCR) in 15 days or more after the second dose of vaccine was taken as the primary outcome measure.

Results showed that the overall efficacy of the vaccine in preventing Covid symptoms ≥15 days after the second dose was 74%, while the efficacy in persons aged 65 years or older was 83.5%.

There were no cases of severe or critical Covid among the subgroup of 17,662 persons who had been fully vaccinated, whereas there were 8 such cases among the 8550 participants in the placebo group. and had significantly fewer Covid-19–related emergency department visits, hospitalizations, and ICU admissions than participants who received placebo.

The vaccine was 64.3% effective in preventing SARS-CoV-2 infection. Also, both SARS-CoV-2 spike protein binding and neutralizing antibodies increased in all age groups after the first dose of AZD1222 and further increased from baseline when measured 28 days after the second dose.

The adverse events were mostly mild or moderate in nature and there was no evidence of increased overall risk of neurologic events or thrombosis/thrombosis with thrombocytopenia in the trial.

This phase III trial has confirmed the safety and efficacy of the Oxford-AstraZeneca vaccine is effective in preventing symptomatic Covid-19 as well as severe/critical disease and hospitalizations across all age groups.

Reference

1. Falsey AR, et al; AstraZeneca AZD1222 Clinical Study Group. Phase 3 safety and efficacy of AZD1222 (ChAdOx1 nCoV-19) Covid-19 vaccine. N Engl J Med. 2021 Sep 29. doi: 10.1056/NEJMoa2105290