AstraZeneca COVID-19 Vaccine Safe and Efficacious in Adult Populations


Investigators reported that the vaccine prevented symptomatic and severe cases of COVID-19 in several populations including older patients.

Ann Regina Falsey, MD,

Ann Regina Falsey, MD

New data published in The New England Journal of Medicine confirmed that the AZD1222 (ChAdOx1 nCoV-19) COVID-19 vaccine was safe and efficacious in preventing symptomatic and severe COVID-19 across several populations including older adult patients.

The ongoing study led by Ann Regina Falsey, MD, of the Department of Medicine, Infectious Diseases at the University of Rochester Medical Center, New York, sought to define the safety and efficacy of the vaccine in a large, diverse population at increased risk for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.

Previous Studies

The study was founded on several studies that tested the overall effectiveness of the Pfizer and AstraZeneca COVID-19 vaccines.

A recent study conducted by investigators from Public Health England found that 1 dose of either of the vaccines significantly reduced effectiveness against the recently discovered Delta variant, with investigators utilizing a test negative case control design for the study.

After 2 doses of the Pfizer vaccine, a reduced dose effectiveness was observed in participants, dropping from 93.4% against Alpha to 87.9% against Delta.

Another study from London discovered that single doses of the vaccine provided significant protection against disease in older adult patients.

Additionally, recent complications of the AstraZeneca COVID-19 vaccine were reported in April, with a contemporary assessment asserting that 11 European patients experienced thrombosis or thrombocytopenia after vaccination.

The AstraZeneca Study

In the present study, Falsey and investigators investigated the safety, efficacy, and immunogenicity of 2 doses of AZD1222 compared to placebo in preventing severe COVID-19 complications 15 days or more after the second dose.

A total of 32,451 participants from various locations in the United States, Chile, and Peru were enrolled in the study.

Participants underwent randomization in a 2:1 ratio to receive either the vaccine (n = 21,635) or placebo (n = 10,816).

The team reported low incidences of serious and medically attended adverse events in participants, with any recorded incidences bearing similarities to those observed in the placebo group.

Falsey and colleagues noted that solicited local and systemic reactions were generally mild or moderate in both groups.

The overall efficacy of the AZD1222 COVID-19 vaccine was 74%, with estimated vaccine efficacy being 83.5% in participants 65 years or older.

High vaccine efficacy was recorded was consistent across the myriad of demographic subgroups, with the estimated vaccine efficacy for preventing infection being 64.3%.

Additionally, no severe or critical symptomatic COVID-19 cases were observed in the 17, 662 participants in the AZD1222 group who were fully vaccinated, while 8 cases were noted in the placebo group.

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