Thread by @TimHarford

1/ What a difference a few weeks makes. In mid-December, I asked a collection of wise guests on my BBC radio programme How to Vaccinate the World about the importance of second doses. bbc.co.uk/programmes/m00…

2/ At that stage, only economists - notably @Atabarrok – were suggesting giving people single doses of a vaccine instead of the recommended pair of doses. My panel roundly rejected this idea.

3/ But in the face of a shortage of doses and a rapidly spreading strain of “Super-Covid”, the scientific mainstream appears to have drifted. The UK’s policy is now to prioritise the first dose and to deliver the second one within three months rather than three weeks.

4/ Cynics argue that this change is a wearingly familiar display of dishonesty and short-termism, but many scientists have given the move their approval. Others remain sceptical and are alarmed.

5/ There are several different issues to untangle here. The first is the short-term benefit of the shift to what we might call “first dose first”.

6/ That depends on how good a single dose is in the short term (pretty good it seems), whether it will still be good enough for elderly people (we don’t know) and whether a delay will ruin the booster effect of the second dose (we don’t know that, either; it might even help).

7/ Cars are better with two headlights, and bicycles are better with two wheels. But a car with only one headlight might be good enough in a pinch. The judgment here is that a single dose is more like a car with a single headlight than a bike with a single wheel.

8/ Given that these vaccines may prevent the spread of the virus as well as preventing disease, it is possible that even people at the head of the queue might benefit if their second dose was temporarily redirected.

9/ If forced to drive in the dark, I would rather that every car on the road had one headlight than some two and some none. With a dangerous virus in wide circulation, we are all driving in the dark.

10/ But the shift to “first dose first” creates other dangers. One is vaccine resistance. A further problem is public trust.

11/ My own instinct has long been that the “first dose first” strategy was worth a try. But I have never believed that “Tim Harford’s instinct” is a sound basis for life-or-death public-health decisions. So the government now needs to step up its gathering of evidence.

12/ We need rigorously randomised trials comparing different doses, delays between doses, and mixed-dose vaccinations too. We can also learn a lot simply by studying what happens to different people who have received different vaccination regimes.

13/ Some of these studies will happen – I’ve just been shown a letter declaring the UK government’s intent to conduct a randomised trial examining the effects of extending the interval before the second dose. Good.

14/ There is nothing wrong with making our best guess. But the government needs to be honest about where the uncertainties lie. It needs to support rapid collection of new evidence to reduce those uncertainties.
timharford.com/2021/01/is-fir…