Impact of COVID vaccine programme

It’s been another big week on the covid front: the government outlined a roadmap to that will see us step back gradually from lockdown to a situation on 21st June when in Boris Johnson’s words “there will be no legal limitations on contact between us”. Nevertheless, some are concerned that the pace is too fast, and schools returning on 8th March is going too far too soon. But what’s certainly influencing the equation now are the vaccine statistics. Close to a third of the adult population have now received at least one dose, and confidence in the initiative received a further shot in the arm this week when data from a preliminary analysis led by Edinburgh University’s Aziz Sheikh showed a dramatic - potentially more than 90% - reduction in cases of Covid-19 hospitalisations among elderly people who’d had the jab…

Aziz - So we were interested in investigating the effects of the first dose of the Covid-19 vaccines. And in particular to study what impact there was on risk of ending up in hospital with Covid-19. So what we've created in Scotland is a cohort of virtually the entire population, 5.4 million people. What we've done is we've linked up their general practice data with the vaccination records, with hospitalisation records. And what we were able to do was track these individuals over time, the group that was vaccinated and the group that was unvaccinated. So we studied over 1.1 million first doses of the vaccine and the outcome of interest in this particular study, that was the risk of ending up in hospital, we were able to establish that for both groups.

Chris - And the results? What did you find?

Aziz - Individuals - whether they were given the Pfizer vaccine or the AstraZeneca vaccine - from day seven onwards, both vaccines were effective in reducing risk of hospitalisation. There is quite a substantial effect in preventing against hospitalisations.

Chris - And how big is substantial?

Aziz - The peak effect that we were seeing was an 85% reduction with the Pfizer-BioNTech vaccine at 28 days, and a peak effect of 94% with the Oxford-AstraZeneca vaccine at the same time point.

Chris - And when you say peak effect, have you got sort of a confidence range here where you think it's at least this and probably not more than this? So what is that range?

Aziz - Let's do the Pfizer-BioNTech one first of all. Confidence intervals around that were 76-91%. And then with the AstraZeneca, they were 73-99%, that's for the corresponding time periods.

Chris - One other country pursuing this quite heavily - Israel - do your results broadly agree with what they're finding?

Aziz - Yes, they do. I mean Israel is slightly ahead of us in that respect and they're implementing the Pfizer-BioNTech vaccine. They're also showing substantial reduction in hospitalisation, but they've also over the weekend reported on reductions in the risk of transmission.

Chris - Now, this kind of protection really matters because if we can not only protect people from developing severe illness, but also stop them actually catching the new coronavirus full stop, this is going to have a very significant effect on our ability to control the spread of the infection, particularly among people who may have no symptoms. And this is really important in settings like hospitals, where an infected staff member could pass the infection to a vulnerable patient. But as Cambridge-based infectious diseases consultant Mike Weekes explains, the jab does cut the number of cases by a very significant margin.

Mike - We specifically examined staff at Addenbrooke's hospital who report well to work without any symptoms of coronavirus. And because we test about four and a half thousand staff a week, we can determine the proportion of people who have asymptomatic infection, infection without any symptoms. And what's happened is that since January, the occupational health department has been organising a mass vaccination campaign. So that by now more than 90% of Addenbrooke's staff are vaccinated with the Pfizer vaccine against Covid-19. And so by combining our testing programme and our vaccination programme, we can answer the question, "If you're vaccinated, are you just prevented from being sick with Covid-19 or are you prevented from being infected with Covid-19?" And that's a really important question because if the vaccine prevents infection, it prevents transmission to others and it prevents transmission to vulnerable patients.

Chris - What's the control group here? 'Cause obviously you've got to compare things with something else in order to know whether or not the vaccine is making a difference. So how are you doing this?

Mike - So what we did was we compared on a week by week basis, people who had and hadn't been vaccinated as the vaccination programme was being rolled out. So our control group was people who weren't vaccinated and the test group was people who were vaccinated.

Chris - First of all then Mike, how many people in total were detected as asymptomatically infected across the period that you studied?

Mike - We specifically looked at a two week period because that's when the number of people in the unvaccinated group was about constant. And so we found about 40 or 50 or so in total who were infected.

Chris - And how does that contrast with people who had been vaccinated? In other words, what is the impact of vaccination on catching and therefore potentially transmitting coronavirus infection?

Mike - There was a four times reduction in the number of people who became infected in the vaccination group compared to the unvaccinated group.

Chris - This must be music to your ears then.

Mike - It's really, really good news actually. Fewer people being infected, particularly fewer people being infected without symptoms, means that they won't go into work completely unaware that they have Covid. It means they won't transmit to their colleagues and they won't transmit to vulnerable patients. And that's four times fewer transmissions.