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T cell and antibody responses induced by a single dose of ChAdOx1 nCoV-19 (AZD1222) vaccine in a phase 1/2 clinical trial

Our take —

This phase 1/2 study demonstrates that a Th1-biased immune response is elicited by a single dose of the ChAdOx1 vaccine (developed by Oxford & AstraZeneca). This is favorable because Th2-biased cytokine secretion has been shown to enhance disease for other coronaviruses, though this has not been demonstrated for SARS-CoV-2. The results here are encouraging, and this vaccine candidate has moved on to ongoing phase 2/3 trials in order to assess its efficacy. Additionally, this vaccine has received Emergency Use Authorization in the UK as well as several other countries, but not yet in the US.

Study design

Randomized Controlled Trial

Study population and setting

Information on study recruitment and participant demographics was previously reported in Folegatti et. al. 2020. Participants ranged from age 18 to 55 and were either given 5×1010 viral particles of the ChAdOx1 vaccine (manufactured by AstraZeneca) or control vaccine (MenACWY). On days 7, 14, 28, and 56 post-vaccination, blood samples were collected for analysis of the immune response.

Summary of Main Findings

Serum from study participants showed Th1-biased cytokine secretion in response stimulation with SARS-CoV-2 spike protein. B cell proliferation was increased at all post-vaccination time points. IgM and IgA antibodies specific to the spike protein were produced, in addition to IgG, which was previously reported. The IgG subclasses are mainly IgG1, found in about half of participants, and IgG3, found in almost all participants. Broad Th1-biased CD4+ and CD8+ T-cell responses specific to the S1 and S2 subunits of the SARS-CoV-2 spike protein were detected. Notably, immune response did not differ based on sex, or with age within this population.

Study Strengths

This study presented a full characterization of the immune response after one dose of the ChAdOx1 vaccine, examining a wide variety of immune system components. The results also included data on if there was a difference in the immune response based upon sex, which is important since COVID-19 seems to affect men more severely than women.

Limitations

The study included a relatively small cohort of participants who were mainly white, and also limited to age 18 to 55 years old. Additionally, little is known about the effectiveness of adenovirus-based viral vectors as vaccines compared to traditional vaccine types.

Value added

A detailed analysis of the immune response after a single dose of the ChAdOx1 vaccine.

This review was posted on: 14 January 2021