The study will include up to 54 healthy adult participants, divided into five groups. Groups 1-3 will consist of vaccine-naïve volunteers and groups 4-5 will consist of volunteers who have received 2 doses of IM COVID-19 vaccine.~Groups 1-3 will receive three vaccine dose levels (low i.e. 5x10^9vp, high i.e. 5x10^10 VP, and moderate i.e. 2x10^10 VP ChAdOx1 nCOV-19 IN). The low and high dose groups will each have safety lead-in subgroups. All volunteers will be consented for receipt of a booster vaccine at approximately 4 weeks post first vaccine. All volunteers will be randomly allocated 1:1 to receive an intranasal booster vaccine as indicated, stratified by first dose level.~Group 4 will consist of volunteers who have received 2 intramuscular doses of ChAdOx1 nCoV-19, at least eight weeks apart, and group 5 will consist of volunteers who have received 2 intramuscular doses of BNT162b, at least three weeks apart. Both of these groups will receive a single standard dose (5x1010vp) on intranasal ChAdOx1 nCOV-19.
Open label, dose escalation study to investigate:~Safety, tolerability and immunogenicity of one or two doses of intranasal ChAdOx1 nCOV-19, in vaccine naïve individuals, with randomisation between one and two dose groups.~Safety, tolerability and immunogenicity of intranasal ChAdOx1 nCOV-19, given as a booster dose in individuals who have had two intramuscular COVID-19 vaccinations.