The company’s statement led with the fact that all 45 subjects (in this analysis) who received doses of 25 micrograms (two doses each), 100 micrograms (two doses each), or a 250 micrograms (one dose) developed binding antibodies.

Later, the statement indicated that eight volunteers — four each from the 25-microgram and 100-microgram arms — developed neutralizing antibodies. Of the two types, these are the ones you’d really want to see.

We don’t know results from the other 37 trial participants. This doesn’t mean that they didn’t develop neutralizing antibodies. Testing for neutralizing antibodies is more time-consuming than other antibody tests and must be done in a biosecurity level 3 laboratory. Moderna disclosed the findings from eight subjects because that’s all it had at that point. Still, it’s a reason for caution.

Separately, while the Phase 1 trial included healthy volunteers ages 18 to 55 years, the exact ages of these eight people are unknown. If, by chance, they mostly clustered around the younger end of the age spectrum, you might expect a better response to the vaccine than if they were mostly from the senior end of it. And given who is at highest risk from the SARS-CoV-2 coronavirus, protecting older adults is what Covid-19 vaccines need to do.