ABSTRACT
Omicron spike (S) encoding vaccines as boosters, are a possible strategy to improve COVID-19 vaccine efficacy against Omicron. Here, non-human primates immunized twenty months earlier with Ad26.COV2.S, were boosted with Ad26.COV2.S, Ad26.COV2.S.529 (encoding Omicron BA.1 S) or a combination of both vaccines. All vaccines elicited a rapid increase in WA1/2020 and Omicron S antibody titers; Omicron BA.1 and BA.2 antibody responses were most effectively boosted by vaccines including Ad26.COV2.S.529. Independent of vaccine used, mostly WA1/2020-reactive or WA1/2020 and Omicron BA.1 cross-reactive B cells were detected. Boosting with vaccines including Ad26.COV2.S.529 provided slightly higher protection of the lower respiratory tract against Omicron BA.1 challenge compared with Ad26.COV2.S. Antibodies and cellular immune responses were identified as complementary correlates of protection. Overall, a booster with an Omicron-spike based vaccine provided moderately improved immune responses and protection compared with the original Wuhan-spike based vaccine, which still provided robust immune responses and protection against Omicron infection.
Subject(s)
Poult Enteritis Mortality Syndrome , COVID-19ABSTRACT
We previously reported that a single immunization with an adenovirus serotype 26 (Ad26) vector-based vaccine expressing an optimized SARS-CoV-2 spike (Ad26.COV2.S) protected rhesus macaques against SARS-CoV-2 challenge. In this study, we evaluated the immunogenicity and protective efficacy of reduced doses of Ad26.COV2.S. 30 rhesus macaques were immunized once with 1×10 11 , 5×10 10 , 1.125×10 10 , or 2×10 9 vp Ad26.COV2.S or sham and were challenged with SARS-CoV-2 by the intranasal and intratracheal routes. Vaccine doses as low as 2×10 9 vp provided robust protection in bronchoalveolar lavage, whereas doses of 1.125×10 10 vp were required for protection in nasal swabs. Activated memory B cells as well as binding and neutralizing antibody titers following vaccination correlated with protective efficacy. At suboptimal vaccine doses, viral breakthrough was observed but did not show evidence of virologic, immunologic, histopathologic, or clinical enhancement of disease compared with sham controls. These data demonstrate that a single immunization with a relatively low dose of Ad26.COV2.S effectively protected against SARS-CoV-2 challenge in rhesus macaques. Moreover, our findings show that a higher vaccine dose may be required for protection in the upper respiratory tract compared with the lower respiratory tract.