The data is of very little use without a control. You could compare it to overall Coronavirus death rates, but those numbers are biased in all sorts of ways (for instance, fully asymptomatic cases).

I would disagree with "very little use". Uncontrolled trials are done all the time. You basically collect "nature history" data and compare it to that.

In addition, the mechanism of vaccines is very well know. You can vaccinate and measure antibody formation.

You could still develop a vaccine without a control and have confidence that it works.

Pretty sure uncontrolled trials are common at the latest stages of drug development. It's called a single-arm trial.

Source: I once participated in a phase III open-label single-arm trial.

They exist, but are usually not sufficient to support a drug or vaccine approval.

The standard is two well controlled studies, but additional open label trials may be used to address specific health authority concerns.

If you are interested, you can look up the other trials the drug may have gone through.