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  Authors:S.P. Graham et al. 

Journal/ Pre-Print:bioRxiv 

Key Words:vaccination, ChAdOx1 nCoV-19 

Research Highlights 

  1. A booster immunisation 28 days post prime vaccination slightly increases spike-peptide reactive CD4 and CD8 T cell numbers in pigs, but not in mice. 

  1. The booster immunisation enhanced binding antibody titers in BALB/c mice and pigs, with a concomitant significant increase in SARS-CoV-2 neutralising titres in pigs.  


Immunogenicity of a single administration of the adenoviral vector expressing SARS-CoV-2 spike protein (ChAdOx1 nCoV-19) was demonstrated previously in macaques. Here, the effect of a booster administered 28 days post initial immunisation is determined in mice and pigs. The booster immunisation slightly increases spike-peptide reactive CD4 and CD8 T cell numbers in pigs, but not in mice. It did enhance the antibody responses, particularly in pigs, with a significant increase in SARS-CoV-2 neutralising titres. 

Impact for SARS-CoV2/COVID19 research efforts  

Develop a vaccine for SARS-CoV2/COVID19 

Study Type  

  • In vitro study 

  • In vivo study; BALB/c and CD1 mice, and pigs 

Strengths and limitations of the paper 

Novelty: A prime-boost strategy is more effective than a single dose of ChAdOx1 nCoV-19 

Standing in the field:An increase in immune response is expected upon booster. Interestingly, the Moderna vaccine prime+booster has superior antibody titers, whereas ChAdOx1 nCoV-19 has superior cellular responses.  

Appropriate statistics: Appropriate; ANOVA or a mixed-effects model were conducted to 

compare responses over time and between vaccine groups at different time points post-vaccination. 

Viral model used:Lentiviral-based SARS-CoV-2 pseudoviruses for neutralisation responses 

SARS-CoV-2 isolate England-2 stocks also used for neutralisation responses 

Translatability:ChAdOx1 nCoV-1 is in phase I clinical trials and already cGMP produced by AstraZeneca. 

Main limitations: Authors have not demonstrated protection after prime and booster vaccine to a challenge of the pigs (not sure if possible) or at least the mice (with mouse-adapted SARS-CoV-2)  

Low number of pigs. 

No clear marking of significance in the figures. 

Limited data.