On May 26, 2021, Altimmune announced new results from a preclinical study demonstrating the ability of its AdCOVID vaccine candidate to neutralize the rapidly emerging SARS-CoV-2 B.1.351 variant of concern that originated in South Africa. B.1.351 carries multiple mutations in the receptor binding domain including the E484K mutation that has been shown to substantially decrease the ability of authorized vaccines to neutralize the virus.

In the current study, performed in collaboration with investigators at Saint Louis Univenrsity, the neutralizing titer against the B.1.351 variant virus was only 4.4-fold lower than the neutralizing titer against an original or ancestral Wuhan-like isolate when measured seven weeks after a single intranasal dose of AdCOVID. Furthermore, in mice that received a booster dose of AdCOVID, the reduction in the neutralizing titer against the B.1.351 variant was only 1.8-fold lower at seven weeks post vaccination; statistically the same as the neutralization titer against the Wuhan isolate. The serum neutralizing antibody titers were determined using a live virus focus reduction neutralization titer (FRNT) assay with a 50% neutralization endpoint.

Importantly, AdCOVID also promoted a strong mucosal neutralizing response to the B.1.351 virus in the respiratory tract with bronchoalveolar lavages showing neutralization of the variant virus. These preclinical data suggest that vaccination with AdCOVID leads to a cross-neutralizing antibody response both systemically and locally within the respiratory tract that can effectively neutralize the B.1.351 virus.