We have become used to Mondays bringing good news on the vaccine front. But the publication of interim results from the AstraZeneca/Oxford University vaccine — AZD1222 — will certainly please the British government.

Not merely because this is the home-grown option and the UK has already ordered 100 million shots, but because, shot for shot, it is considerably cheaper to buy and administer than the other vaccine candidates. The vaccine itself is less than a fifth of the price of the Pfizer vaccine. Moreover, it does not need storing and transporting at -94°F — it can be kept at ordinary fridge temperatures (35 to 46°F), greatly facilitating any roll-out. This will be even more important when it comes to administering the vaccine globally — in developing countries AstraZeneca, for now, looks like the obvious choice.

Set against that good news, the interim results are not as impressive as those of the Pfizer and Moderna trials. The interim trials recorded an efficacy rate of 90 percent when volunteers were given a half dosage followed by a full shot at least a month later. When people were given two full shots, also a month apart, that fell to 62 percent. This led to an average efficacy of 70 percent. That the half dosage regime is more effective can be interpreted as good news, in that it means supplies can be stretched further. But it is slightly concerning that the scientists involved seem to have no idea why this should be the case — it suggests there is a lot of work on this vaccine still to be done.

Could there be an even more successful dosing regime? As with the other two vaccines, all we have for the moment is a press release, with full published results to come.

It is worth noting that the AstraZeneca results released so far are based on a smaller sample compared with the others: 23,000, compared with 30,000 for Moderna and 43,000 for Pfizer. Moreover, with the Oxford vaccine, only 2,741 volunteers were administered with the more successful half shot followed by full shot regime. Far more — 8,895 — were given the two full shots. Given that the interim results are based on a total of just 131 cases of COVID-19, quite small numbers are involved. The AstraZeneca results are two separate trials, one in the UK and one in Brazil.

What does this morning’s news mean for the speed of a vaccine rollout? In theory, it could mean more time before we get population-wide immunity for the AstraZeneca vaccine, in the sense that the two shots are given a month apart — rather than three weeks in the case of Pfizer (Moderna is also one month). But having three available vaccines, one much easier to distribute than the others, should help speed things up. It is interesting that British ministers are now speaking of April as the date by which life might return to normal, suggesting they think they can get a majority of the population immunized by then.

What we don’t know about any of these vaccines yet is how long immunity will last. Epidemiologists will be continuing to study all these vaccines while they are administered on a population-wide level to see signs of which is the most effective in the long term. If one provides immunity lasting months and another years, the relative costs of each could shift dramatically.

This article was originally published onThe Spectator’s UK website.