Arbutus might now look like a contender in hepatitis B, after the release of phase I data for the 60mg dose of its lead candidate, AB-729. On the surface the results, which prompted a 36% share price rise, show that patients can benefit from this, a welcome development given the toxicity signals AB-729 has thrown up at 180mg. However, with the impressive HBsAg decline of 0.99 log10 – one of the proxies for functional cure levels – having been driven by an outlier, it is still not clear how efficacious AB-729 is. Additional clarity might be offered by trials looking at multiple administrations of the 60mg dose and a single 90mg shot; data from these are due in the second half of 2020. Positive results would indicate that the 0.99 log10 reduction is not a fluke. Questions around safety could be answered too, given the higher dosing. While after two earlier failures the company's discovery of a functional hep B cure would be handsomely rewarded, investors who have piled back into Arbutus – the sector’s cheapest hep B stock – might be wise to wait for more data before committing more funds.