ChAdOx1 nCoV-19

showed an acceptable safety profile and induced both humoral and cellular immune responses

Systemic adverse effects were less common in adults aged ≥56 years. No serious adverse effect related to the vaccine were observed. Median anti-spike protein (SARS-CoV-2) IgG and neutralising antibody levels 28-days post boost immunization were similar across all age cohorts. >99% of boosted patients had neutralising antibodies by day 14 post boost. T-cell responses peaked at day 14 after a single standard dose. The vaccine is recommended for further efficacy assessment in all age groups and individuals with comorbities. Sample size: Low dose: 50 + 49 control (two doses, 18-55 age group); 30 + 10 control (one dose, 56-69 age group); 30 + 10 control (two doses, 56-69 age group); 50 + 10 control (one dose, 70+ age group); 46 + 10 (two doses, 70+ age group); Standard dose:  49 + 9 control (two doses, 18-55 age group); 30 + 10 control (one dose, 56-69 age group); 30 + 10 control (two doses, 56-69 age group); 50 + 10 control (one dose, 70+ age group); 49 + 10 (two doses, 70+ age group). Dosage: Low dose: 2.2e10 virus particles; standard dose: 3.5–6.5e10 virus particles; cohorts received a single or two doses 28 days apart (see Sample size). Endpoints: Safety and humoral and cellular immunogenicity; efficacy (symptomatic COVID-19 cases).

ChAdOx1 nCoV-19 has an acceptable safety profile and has been found to be efficacious against symptomatic COVID-19 in this interim analysis of ongoing clinical trials.

After a single dose of vaccine cellular and humoral responses were observed. The response was Th1-biased, with strong interferon gamma and tumor necrosis factor alpha secretion by CD4+ T cells. IgG1 and IgG3 subclasses dominated the antibody response. Various CD8+ T cells were also induced.

A single intramuscular dose elicited a SARS-CoV-2 Spike-specific immune response in adult mice characterized by specific B- and T-cell responses, with formation of plasma cells, germinal centres, and follicular Th cells. In aged mice, the response was similar, but an impairment in germinal centre formation and production of CD8+ T-cells secreting granzyme B was observed. Boosting reduced this impairment.

The overall vaccine efficacy >14 days post second dose was 66.7%. The efficacy for a time interval of 22-90 days after a single dose was 76% (the value is not directly comparable with the two-dose regimen due to the trial format). In the subjects who had received 2 doses the efficacy was higher (81.3%) for a longer prime-boost interval (≥12 weeks) than for a shorter one (55.1%; <6 weeks). No hospital admissions were reported in the vaccinated group. Sample size: 8,597 + 8,581 control. Primary outcome: Confirmed symptomatic infection more than 14 days after the second dose.

Although a 2.5-fold decrease in neutralization titres against B.1.1.7 strain was observed compared to an early Wuhan-related strain, the neutralization remained robust, and no evidence of vaccine escape was observed.

The vaccine efficacy in preventing symptomatic nucleic acid amplification-positive COVID-19 infection was 70.4% for B.1.1.7 strain infection and 81.5% for non-B.1.1.7 infection (mostly BetaCoV/Australia/VIC01/2020 (“Victoria”)) lineage). The sera of vaccinated adults displayed lower neutralization capacity against the B.1.1.7 strain. Sample size: 4244 + 4290 control (primary efficacy cohort), of which there were 311 confirmed SARS-CoV-2 infections. Dosage: Two dose regimen. Primary outcome: Symptomatic COVID-19.

2 doses of the AstraZeneca vaccine were 60% effective against symptomatic disease from the B.1.617.2 variant compared to 66% effectiveness against the B.1.1.7 variant.

The sera of individuals who were primed by this vaccine and boosted by BNT162b2 were more efficient in inhibiting Omicron Spike-mediated cell entry in vitro compared to BNT162b2 prime and boost-vaccinated individuals’ sera. The efficiency was lower compared to the B.1 strain Spike, however. 

Although the capacity of sera of vaccinated individuals markedly decreased for the omicron strain after a two-dose regimen, a third (booster) vaccination significantly increased omicron neutralization in vitro. 

Sera from vaccinated individuals were capable of B.1.1.7 strain neutralization in vitro, despite a modest decrease in neutralization capacity compared to the Victoria strain. 

Neutralization titres against the Beta strain of SARS-CoV-2 were significantly lower compared to the original strain. A majority of samples still neutralized the virus, however.