The two vaccines approved and in use in Britain showed high efficacy rates in trials, but it takes time for data to creep through on efficacy in the real-world. We are, however, getting the first figures trickling through. This morning comes a paper evaluating the effectiveness of the Pfizer-BioNTech and AstraZeneca-Oxford vaccines in preventing hospitalisation rates in the Scottish population, using a dataset that covers 5.4 million people, 99 per cent of the population.
The Eave II study, led by the University of Edinburgh, followed the 650,000 people who received the Pfizer vaccine between 8 December and 15 February and the 490,000 people who received the AstraZeneca vaccine between 4 January and 15 February. The Pfizer vaccine was estimated to have reduced hospitalisations by 85 per cent between days 28 and 34 after the first dose. The AstraZeneca vaccine was found to reduce them by 94 per cent.
The results are notable not only because they show that both vaccines are highly effective on a population-wide scale; they also suggest that the AstraZeneca vaccine is slightly better than the Pfizer vaccine at preventing hospitalisations. This is the other way around from the trial data, which suggested the Pfizer vaccine was more efficacious than the AstraZeneca one — contributing to the reluctance of many EU countries to roll out the latter to their populations, and the reluctance of some healthcare staff in France and Germany to accept it.
The headline figures from the trials concentrated on symptomatic infections, while the Eave II study looked only at hospitalisations, which is one difference. Moreover, a note of caution needs to be read into the results, which were not intended to compare the efficacy of the two vaccines and which have a margin of error. The 85 per cent figure for Pfizer sits in a 95 per cent confidence interval of 76 per cent to 91 per cent; the 94 per cent figure for AstraZeneca sits in a respective margin of 73 per cent to 99 per cent. The data for the AstraZeneca vaccine is more sparse because that vaccine only started to be administered on 4 January.The study produced a combined figure for the over 80s: those given either of the vaccines were found to be 81 per cent less likely to end up in hospital after 28 to 34 days.
There are limitations to the study, which has not yet been peer-reviewed but has been published as a pre-print. Thanks to the high uptake of the vaccines there is limited data on over 80s who, for one reason or another, did not have the vaccine. At the other end of the scale, there are relatively few under 70s who had the vaccine within the period of the study — and those that did are mostly in specific groups, such as healthcare workers and people with serious medical conditions.
Nonetheless, real-world data is extremely welcome. The fact that it backs data from the vaccine trials — and that it shows good efficacy after one dose — will come as huge relief to the government. As I wrote here last week, we also have a real-world study from Israel that also suggests good efficacy of the Pfizer vaccine after one dose.