Another SARS-CoV-2 Vaccine Candidate Shows Promise in Phase 1/2 Trial

Another SARS-CoV-2 vaccine candidate has shown promise in a phase 1/2 trial performed in the United Kingdom. The findings of the trial were published in The Lancet.

The vaccine candidate “showed an acceptable safety profile, and homologous boosting increased antibody responses,” results which “support large-scale evaluation of this candidate vaccine in an ongoing phase 3 program,” according to the researchers.

These findings emerged from a phase 1/2, single-blind, randomized controlled trial (N = 1077), which included healthy adults aged 18 to 55 years without history of laboratory confirmed SARS-CoV-2 or COVID-19-like symptoms. Participants were randomly assigned to receive a chimpanzee adenovirus-vectored vaccine (ChAdOx1 nCoV-19; n = 543) expressing the SARS-CoV-2 spike protein or a meningococcal conjugate vaccine (MenACWY; n = 534). At 2 of the 5 study sites, prophylactic paracetamol was allowed to be administered prior to vaccination due to a protocol amendment.

In addition, 10 participants who had been assigned to a non-randomized, unblended ChAdOx1 nCoV-19 prime-boost group were given a 2-dose schedule, during which the booster vaccine was administered 28 days after dose 1.

The co-primary outcomes of the trial were defined as efficacy (determined by cases of symptomatic virologically confirmed COVID-19) and safety (determined by the occurrence of serious adverse events) after 28 days.

Spike-specific T-cell responses peaked on day 14 in the ChAdOx1 nCoV-19 group, with a median 856 spot-forming cells per million peripheral blood mononuclear cells. Anti-spike IgG responses had increased by day 28 and were boosted after dose 2 was administered.

When measured in the microneutralization assay MNA₈₀, neutralizing antibody responses against SARS-CoV-2 were detected among 32 (91%) of 35 participants after dose 1. When measured in the plaque reduction neutralization assay PRNT₅₀, these responses were detected in 35 (100%) participants. The researchers noted that all participants had neutralizing activity after receiving a booster dose (all 9 participants in MNA₈₀ at day 42 and all 10 participants in Marburg VN microneutralization assay at day 56). Neutralizing antibody responses were found to correlate strongly with antibody levels measured by enzyme-linked immunosorbent assay.

Local and systemic reactions, including feeling feverish, pain, muscle ache, chills, malaise, and headache, occurred more commonly in the ChAdOx1 nCoV-19 group. However, many of these reactions were reduce with the use of prophylactic paracetamol. No serious adverse events associated with ChAdOx1 nCoV-19 occurred.

—Christina Vogt

Reference:
Folegatti PM, Ewer KJ, Aley PK, et al. Safety and immunogenicity of the ChAdOx1 nCoV-19 vaccine against SARS-CoV-2: a preliminary report of a phase 1/2, single-blind, randomised controlled trial. Lancet. Published online July 20, 2020. doi:10.1016/S0140-6736(20)31604-4