Safety and immunogenicity of a first-generation modified vaccinia virus Ankara-vectored SARS-CoV-2 vaccine candidate with mRNA-based booster vaccination: A phase 1 trial.
Anahita Fathi, Christine Dahlke, Leonie Mayer et al.
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In 30 seconds
This phase 1 trial assessed safety and immune responses to the MVA-vectored SARS-CoV-2 vaccine MVA-SARS-2-S in 30 healthy, SARS-CoV-2-naive adults given two doses 28 days apart, with six-month follow-up. The vaccine was well tolerated, with no severe or serious adverse events, but elicited limited immune responses: S1-specific seroconversion occurred in 0/15 participants receiving 10^7 IU and 3/15 receiving 10^8 IU. In a subgroup of 12, subsequent BNT162b2 boosting induced S1 seroconversion and detectable neutralizing antibody and T-cell responses in all boosted participants.
Key findings
- No severe or serious adverse events occurred after MVA-SARS-2-S vaccination.
- S1-specific seroconversion was 0/15 with 10^7 IU and 3/15 with 10^8 IU.
- Neutralizing antibodies were detected in one participant, in the 10^8 IU group.
- All participants receiving BNT162b2 boosters developed S1 seroconversion and detectable neutralizing antibody and T-cell responses.
Why it matters
The trial illustrates that tolerability does not necessarily translate into adequate immunogenicity: this MVA candidate produced limited S1 and neutralizing antibody responses. The observed responses after mRNA boosting suggest that prior MVA vaccination did not prevent subsequent immune responses in the boosted subgroup, informing evaluation of heterologous vaccine sequences.
What to keep in mind
This was a phase 1 trial in 30 healthy, SARS-CoV-2-naive adults; the BNT162b2 booster subgroup included 12 participants.