Safety and humoral immunogenicity of the ChAdOx1 nCoV-19 vaccine administered as a fourth dose booster following two doses of ChAdOx1 nCoV-19 and a third dose of BNT162b2 (COV009): A prospective cohort study.
Feng S., Bibi S., Aley PK., Cappuccini F., Clutterbuck EA., Conlin K., Ebrahimi N., Eordogh A., Faust SN., Felle S., Green J., Gill H., Mujadidi Y., Oladunjoye I., Owino N., Plested E., Robinson H., Stuart A., Voysey M., Pollard AJ., Lambe T.
OBJECTIVES: Evaluation of the safety and humoral immunogenicity of ChAdOx1 nCoV-19 as a fourth dose booster in individuals who have had two initial doses of the vaccine and a third dose of BNT162b2. METHODS: COV009 is a safety follow-up study of volunteers enroled in the pivotal pre-licensure ChAdOx1 nCoV-19. In this sub-study, 149 eligible participants were given a fourth dose of ChAdOx1 nCoV-19. Primary outcomes were reactogenicity, safety, and humoral immunogenicity. Anti-spike IgG and pseudo-neutralising antibody against multiple variants were measured from pre-first dose to 28 days post-second and post-fourth dose (third dose samples were unavailable). RESULTS: A fourth dose of ChAdOx1 nCoV-19 had an acceptable safety profile with no vaccine-related serious adverse events. Humoral responses against various SARS CoV-2 variants post-fourth dose were significantly increased compared with the responses after the second dose (7- to 9-fold increase for anti-spike IgG responses across variants, all p<0.05). Those with lower antibody levels prior to the 4th dose had stronger responses to a 4th dose booster. Seropositivity by anti-nucleocapsid, or higher antibody responses pre-fourth dose correlated with lower infection risks six months thereafter (OR: 0.16, 95% CI: 0.05, 0.50). CONCLUSIONS: The ChAdOx1 nCoV-19 fourth dose is well tolerated and boosts humoral immunity; this was evident as an increased humoral response across multiple variants of concern. These data support its use as a booster dose against SARS-CoV-2 infection.