The good news is that several potential coronavirus vaccines are at the “widespread human trial” stage. The bad news is that in the case of at least one of them, that trial is running into some trouble:

Experts have been particularly concerned about AstraZeneca’s vaccine trials, which began in April in Britain, because of the company’s refusal to provide details about serious neurological illnesses in two participants, both women, who received its experimental vaccine in Britain. Those cases spurred the company to halt its trials twice, the second time earlier this month. The studies have resumed in Britain, Brazil, India and South Africa, but are still on pause in the U.S. About 18,000 people worldwide have received AstraZeneca’s vaccine so far.

The illness in question is something called transverse myelitis – a rare degenerative illness of the spinal cord that usually affects about one in every 236,000 people. But now two people out of 18,000 have been diagnosed with it in a vaccine trial. That’s the kind of statistical anomaly that stops these things in their tracks.

Of course, it’s bad news for those of us who want a vaccine soon, but the more important thing is that it’s good news for those of us who also want a vaccine to be safe. The whole point of the trials, after all, is twofold: To see if the vaccine works, and to see if it is safe.

But in the case of the Astrazeneca vaccine candidate, there are small concerns now on both of those fronts. The transverse myelitis anomaly will obviously have people worrying about safety. But there’s also a question mark over its effectiveness:

AstraZeneca’s 111-page trial blueprint, known as a protocol, states that its goal is a vaccine with 50 percent effectiveness — the same threshold that the Food and Drug Administration has set in its guidance for coronavirus vaccines. To determine with statistical confidence whether the company has met that target, there will have to be 150 people ill with confirmed coronavirus among participants who were vaccinated or received placebo shots…..

….. Dr. Topol said AstraZeneca’s plan, like those of Moderna and Pfizer, had a problematic feature: All count relatively mild cases of Covid-19 when measuring efficacy, which may hamper efforts to determine whether the vaccine prevents moderate or severe illness.

In plain English, what they’re saying is that they don’t know whether the vaccine works to stop Coronavirus altogether, or whether it only stops it in those who would otherwise only have a mild case anyway. That’s kind of important.

To some extent, all of this is normal, and good. The evidence in relation to the transverse myelitis seems to point towards it being an anomaly – one of the two women, it turns out, had undiagnosed multiple sclerosis. But they’ll still have to slow things down to rule the vaccine out as a cause, in the best case scenario.

The thing is, though, that this is why pinning our economic hopes on an early vaccine is foolish.

The concerns about the Astrazeneca trial in that New York Times story are not limited to simply the Astrazeneca vaccine candidate. Basically all the vaccine candidates at the moment incorporate the same basic ingredients, and the same trial methodology. If the transverse myelitis issue turns out to be more than co-incidence, then that impacts all of them. And finding out for sure whether it was just a coincidence will take months.

Stay tuned, but for now, the news on a vaccine is, well, not great.