inclusion criteria: * able and willing to comply with all study requirements. * willing to allow investigators to discuss medical history with their general practitioner and access all relevant medical records. * willing and able to give informed consent. * women of child-bearing potential must agree not to have sexual intercourse with men, or must consistently use an agreed method of contraception, from at least 28 days prior to enrolment in the study, through 3 months after the last vaccination. * room air oxygen saturation \> 95% at screening/day 0. * seasonal flu vaccine co-administration sub-study only: participant should not have received a current season flu vaccine, should have no reason why the specific sub-study flu vaccine cannot be administered, and should not have any prior history of allergy or severe reaction to seasonal flu vaccines.

inclusion criteria: * able and willing to comply with all study requirements. * willing to allow investigators to discuss medical history with their general practitioner and access all relevant medical records. * willing and able to give informed consent. * women of child-bearing potential must agree not to have sexual intercourse with men, or must consistently use an agreed method of contraception, from at least 28 days prior to enrolment in the study, through 3 months after the last vaccination. * room air oxygen saturation \> 95% at screening/day 0. * seasonal flu vaccine co-administration sub-study only: participant should not have received a current season flu vaccine, should have no reason why the specific sub-study flu vaccine cannot be administered, and should not have any prior history of allergy or severe reaction to seasonal flu vaccines.

inclusion criteria: - able and willing to comply with all study requirements. - willing to allow investigators to discuss medical history with their general practitioner and access all relevant medical records. - willing and able to give informed consent. - women of child-bearing potential must agree not to have sexual intercourse with men, or must consistently use an agreed method of contraception, from at least 28 days prior to enrolment in the study, through 3 months after the last vaccination. - room air oxygen saturation > 95% at screening/day 0. - seasonal flu vaccine co-administration sub-study only: participant should not have received a current season flu vaccine, should have no reason why the specific sub-study flu vaccine cannot be administered, and should not have any prior history of allergy or severe reaction to seasonal flu vaccines.

inclusion criteria: - able and willing to comply with all study requirements. - willing to allow investigators to discuss medical history with their general practitioner and access all relevant medical records. - willing and able to give informed consent. - women of child-bearing potential must agree not to have sexual intercourse with men, or must consistently use an agreed method of contraception, from at least 28 days prior to enrolment in the study, through 3 months after the last vaccination. - room air oxygen saturation > 95% at screening/day 0. - seasonal flu vaccine co-administration sub-study only: participant should not have received a current season flu vaccine, should have no reason why the specific sub-study flu vaccine cannot be administered, and should not have any prior history of allergy or severe reaction to seasonal flu vaccines.

inclusion criteria: - able and willing to comply with all study requirements. - willing to allow investigators to discuss medical history with their general practitioner and access all relevant medical records. - willing and able to give informed consent. - women of child-bearing potential must agree not to have sexual intercourse with men, or must consistently use an agreed method of contraception, from at least 28 days prior to enrolment in the study, through 3 months after the last vaccination. - seasonal flu vaccine co-administration sub-study only: participant should not have received a current season flu vaccine, should have no reason why the specific sub-study flu vaccine cannot be administered, and should not have any prior history of allergy or severe reaction to seasonal flu vaccines.

inclusion criteria: - able and willing to comply with all study requirements. - willing to allow investigators to discuss medical history with their general practitioner and access all relevant medical records. - willing and able to give informed consent. - women of child-bearing potential must agree not to have sexual intercourse with men, or must consistently use an agreed method of contraception, from at least 28 days prior to enrolment in the study, through 3 months after the last vaccination. - seasonal flu vaccine co-administration sub-study only: participant should not have received a current season flu vaccine, should have no reason why the specific sub-study flu vaccine cannot be administered, and should not have any prior history of allergy or severe reaction to seasonal flu vaccines.