• Safety and tolerability of ChAdOx1 Zika given as a standalone vaccine or co-administered with ChAdOx1 Chik at different doses in healthy adult volunteers assessed by the occurrence of solicited adverse events. [ Time Frame: Assessment of solicited AEs in the first 7 days post vaccination. ]
  Occurrence of solicited local and systemic adverse events (i.e: pain, redness, swelling and pruritus at injection site and temperature, feverishness, myalgia, arthralgia, malaise, headache and nausea).
• Safety and tolerability of ChAdOx1 Zika given as a standalone vaccine or co-administered with ChAdOx1 Chik at different doses in healthy adult volunteers assessed by the occurrence of unsolicited adverse events. [ Time Frame: Unsolicited AEs to be assessed up to 28 days post vaccination. ]
  Occurrence of unsolicited local and systemic adverse events
• Safety and tolerability of ChAdOx1 Zika given as a standalone vaccine or co-administered with ChAdOx1 Chik at different doses in healthy adult volunteers assessed by the occurrence of serious adverse events. [ Time Frame: SAEs will be collected from enrolment until the end of the follow-up period (i.e. 6 months) ]
  Occurrence of serious adverse events
• Safety and tolerability of ChAdOx1 Zika given as a standalone vaccine or co-administered with ChAdOx1 Chik at different doses in healthy adult volunteers assessed by the occurrence of laboratory adverse events. [ Time Frame: At Day 0 (baseline), day 2, day 7 and day 28 post vaccination ]
  Occurrence of laboratory adverse events defined as clinically significant changes from baseline. Haematology (Full Blood Count) and Biochemistry (Kidney and Liver Function Tests) will be assessed.

• Safety and tolerability of ChAdOx1 Zika given as a standalone vaccine or co-administered with ChAdOx1 Chik at different doses in healthy adult volunteers assessed by the occurrence of solicited adverse events. [ Time Frame: Assessment of solicited AEs in the first 7 days post vaccination. ]
  Occurrence of solicited local and systemic adverse events (i.e: pain, redness, swelling and pruritus at injection site and temperature, feverishness, myalgia, arthralgia, malaise, headache and nausea).
• Safety and tolerability of ChAdOx1 Zika given as a standalone vaccine or co-administered with ChAdOx1 Chik at different doses in healthy adult volunteers assessed by the occurrence of unsolicited adverse events. [ Time Frame: Unsolicited AEs to be assessed up to 28 days post vaccination. ]
  Occurrence of unsolicited local and systemic adverse events
• Safety and tolerability of ChAdOx1 Zika given as a standalone vaccine or co-administered with ChAdOx1 Chik at different doses in healthy adult volunteers assessed by the occurrence of serious adverse events. [ Time Frame: SAEs will be collected from enrolment until the end of the follow-up period (i.e. 12 months) ]
  Occurrence of serious adverse events
• Safety and tolerability of ChAdOx1 Zika given as a standalone vaccine or co-administered with ChAdOx1 Chik at different doses in healthy adult volunteers assessed by the occurrence of laboratory adverse events. [ Time Frame: At Day 0 (baseline), day 2, day 7 and day 28 post vaccination ]
  Occurrence of laboratory adverse events defined as clinically significant changes from baseline. Haematology (Full Blood Count) and Biochemistry (Kidney and Liver Function Tests) will be assessed.

• Measures of humoral immunogenicity to the ChAdOx1 ZIKA and ChAdOx1 CHIK vaccines [ Time Frame: At days 0, 7, 14, 28, 56, 90 and 182 + extended visit days 270 and 360 ]
  ELISA to quantify antibodies to ZIKV and CHIKV protein antigens responses to ZIKV and CHIKV protein antigens
• Measures of cellular immunogenicity to the ChAdOx1 ZIKA and ChAdOx1 CHIK vaccines [ Time Frame: At days 0, 7, 14, 28, 56, 90 and 182 + extended visit days 270 and 360 ]
  Ex vivo interferon gamma ELISpot responses to ZIKV and CHIKV protein antigens

• Measures of humoral immunogenicity to the ChAdOx1 ZIKA and ChAdOx1 CHIK vaccines [ Time Frame: At days 0, 7, 14, 28, 90, 182, 270 and 364 ]
  ELISA to quantify antibodies to ZIKV and CHIKV protein antigens responses to ZIKV and CHIKV protein antigens
• Measures of cellular immunogenicity to the ChAdOx1 ZIKA and ChAdOx1 CHIK vaccines [ Time Frame: At days 0, 7, 14, 28, 90, 182, 270 and 364 ]
  Ex vivo interferon gamma ELISpot responses to ZIKV and CHIKV protein antigens

• Zika
• Chikungunya

• Biological: ChAdOx1 Zika
  Single dose of ChAdOx1 Zika at different concentrations: 5 x 10^9 vp, 2.5 x 10^10 vp, 5 x 10^10 vp
• Biological: ChAdOx1 Zika, ChAdOx1 Chik
  Co-administration of ChAdOx1 Zika and ChAdOx1 Chik at different concentrations: 5 x 10^9 vp, 2.5 x 10^10 vp, 5 x 10^10 vp

• Experimental: Group 1
  Volunteers will receive standalone dose of ChAdOx1 Zika 5 x 10^9 vp vaccination intramuscularly.
  Intervention: Biological: ChAdOx1 Zika
• Experimental: Group 2
  Volunteers will receive standalone dose of ChAdOx1 Zika 2.5 x 10^10 vp vaccination intramuscularly.
  Intervention: Biological: ChAdOx1 Zika
• Experimental: Group 3
  Volunteers will receive standalone dose of ChAdOx1 Zika 5 x 10^10 vp vaccination intramuscularly.
  Intervention: Biological: ChAdOx1 Zika
• Experimental: Group 4
  Volunteers will receive co-administration dose of ChAdOx1 Zika 5 x 10^9 vp vaccination and ChAdOx1 Chik 5 x 10^9 vp intramuscularly.
  Intervention: Biological: ChAdOx1 Zika, ChAdOx1 Chik
• Experimental: Group 5
  Volunteers will receive co-administration dose of ChAdOx1 Zika 2.5 x 10^10 vp vaccination and ChAdOx1 Chik 2.5 x 10^10 vp intramuscularly.
  Intervention: Biological: ChAdOx1 Zika, ChAdOx1 Chik
• Experimental: Group 6
  Volunteers will receive co-administration dose of ChAdOx1 Zika 5 x 10^10 vp vaccination and ChAdOx1 Chik 5 x 10^10 vp intramuscularly.
  Intervention: Biological: ChAdOx1 Zika, ChAdOx1 Chik

Inclusion Criteria:

• Healthy adults aged 18 to 50 years
• Able and willing (in the Investigator's opinion) to comply with all study requirements
• Willing to allow the investigators to discuss the volunteer's medical history with their General Practitioner or access to this medical history electronically.
• Women of child-bearing potential agree to practice continuous effective contraception (see below) during the study and test negative for pregnancy on the day(s) of screening and vaccination.
• Agreement to refrain from blood donation during the course of the study
• Agreement to inform study team of any impending vaccinations either before or during participation in the study.
• Agreement to refrain from receipt of any flavivirus vaccine throughout the duration of the study (e.g. investigational or licensed Yellow Fever, Japanese Encephalitis, Tick Borne Encephalitis or Dengue virus vaccines).
• Provide written informed consent

Exclusion Criteria:

• Participation in another research study involving receipt of an investigational product in the 30 days preceding enrolment, or planned use during the study period
• Prior receipt of an investigational or licensed vaccine likely to impact on interpretation of the trial data (e.g. Adenovirus vectored vaccine, Zika virus vaccine, Dengue virus vaccine).
• Prior receipt of any vaccines administered ≤30 days before enrolment and/or planned receipt of a vaccine ≤30 days after enrolment.
• Administration of immunoglobulins and/or any blood products within the three months preceding the planned administration of the vaccine candidate
• Any confirmed or suspected immunosuppressive or immunodeficient state, including HIV infection; asplenia; recurrent, severe infections and chronic (more than 14 days) immunosuppressant medication within the past 6 months (inhaled and topical steroids are allowed)
• History of allergic disease or reactions likely to be exacerbated by any component of the vaccine. Any history of anaphylaxis in relation to vaccination.
• History of autoimmune disease.
• Any history of hereditary angioedema, acquired angioedema, or idiopathic angioedema.
• Pregnancy, lactation or willingness/intention to become pregnant during the study
• History of cancer (except basal cell carcinoma of the skin and cervical carcinoma in situ)
• History of serious psychiatric condition likely to affect participation in the study
• Bleeding disorder (e.g. factor deficiency, coagulopathy or platelet disorder), or prior history of significant bleeding or bruising following IM injections or venepuncture
• Any other serious chronic illness requiring hospital specialist supervision
• Suspected or known current alcohol abuse as defined by an alcohol intake of greater than 42 units every week
• Suspected or known injecting drug abuse in the 5 years preceding enrolment
• Seropositive for hepatitis B surface antigen (HBsAg)
• Seropositive for hepatitis C virus (antibodies to HCV)
• Any clinically significant abnormal finding on screening biochemistry or haematology blood tests or urinalysis
• Has history of chronic or acute severe neurologic condition. Including: Neurologic and Neuroinflammatory Disorders: ADEM, including site specific variants, Cranial Nerve Disorders (including paralyses/paresis), GBS (including Miller Fisher Syndrome and other variants), Immune-mediated Peripheral Neuropathies and Plexopathies, Optic Neuritis, Multiple Sclerosis, Narcolepsy, Transverse Myelitis, meningitis, or meningoencephalitis.
• Any other significant disease, disorder or finding which may significantly increase the risk to the volunteer because of participation in the study, affect the ability of the volunteer to participate in the study or impair interpretation of the study data
• Inability of the study team to contact the volunteer's GP to confirm medical history and safety to participate or access this medical history electronically.
• Seropositivity or cross-reactivity to Zika virus or Dengue virus (serology will be requested at the discretion of the investigator).
• Travel to a Zika virus and/or Dengue virus, endemic region in the 30 days prior to screening, until enrolment and in the first 6 months of the participants enrolment in the study (consult clinical team regarding international travel plans)

Additional Exclusion Criteria for Participants also Receiving ChAdOx1 Chik (Groups 4-6)

• Prior exposure to CHIKV (serology will be requested at the discretion of the investigator).
• Prior receipt of an experimental CHIKV vaccine (serology will be requested at the discretion of the investigator).
• Travel to a CHIKV endemic region in the preceding 30 days before screening, until enrolment and in the first 6 months of the participants enrolment in the study (consult clinical team regarding international travel plans)