The next wave of Covid will be different. When cases soared in spring and winter last year lockdowns rapidly brought them back under control. This time it will be vaccines that do the hard work.
But Covid jabs are not a perfect shield. They slow the spread of the virus, help prevent disease, and reduce the risk of dying. They do not bring all this to an end.
In the months ahead many thousands of people will be in hospital with Covid. What may seem more troubling is that ever more will have received two vaccination doses.
This does not mean the immunisations are not doing their job. Real-world data from Public Health England show that two shots of the Oxford/AstraZeneca or of the Pfizer/BioNTech vaccine are 92% and 96% effective, respectively, against hospital admission.
On Thursday, the vaccines minister, Nadhim Zahawi, said the vaccine programme had prevented an estimated 52,000 hospitalisations.
So why will the majority of those in hospital with Covid be double jabbed? There are several factors at work. First of all, who has and has not been vaccinated matters. Across the UK about 30% of adults are not fully vaccinated. While some are vulnerable people who for some reason have not been jabbed, the majority are young, and healthy enough not to be considered at particular risk: these are people who would very rarely get sick enough with Covid-19 to need hospital care.
Looked at another way, the 70% of the population that has been doubled jabbed include the most vulnerable in society. Because the vaccines are not perfect even a small percentage of what scientists call “breakthrough infections” can lead to a large number of hospitalisations – predominantly in this older group.
The total number of Covid hospitalisations will be dramatically lower than in a world without vaccines, but those who are admitted are increasingly likely to have had both shots.
“Imagine if all adults had already been fully vaccinated,” says Kevin McConway, emeritus professor of applied statistics at The Open University. “We know there would still be some hospitalisations, because the vaccines aren’t perfect, but for adults all those hospitalisations would be in vaccinated people. That wouldn’t mean the vaccines don’t help, just that they don’t provide perfect protection – and nobody ever said that they did.”
Public Health England data from early July bears this out. Of 257 deaths from confirmed Delta variant infections between February and late June, only two of the 26 deaths in those under 50 were double jabbed. That compares with 116, or more than half, of the 231 deaths in the over 50s.
“If fully vaccinated, the risk of being hospitalised falls by about 90%,” said Prof David Spiegelhalter, chair of the Winton Centre for Risk and Evidence Communication, at Cambridge University. “But it doesn’t disappear, and as a large proportion of the highest risk people are now vaccinated it’s inevitable they will start to form the majority of the people with Covid in hospital, particularly as most of the unvaccinated people are young and therefore at low risk. Indeed, being young reduces the risk even more than being vaccinated.”
Another big factor at play is age. McConway says the risk of an infected person being hospitalised is at least 10 times, and as much as 25 times greater, for a 75-year-old than a 25-year-old. If the latter risk is on the mark, then a vaccine that prevents 96% of hospitalisations would slash admissions among 75-year-olds to that seen in those 50 years younger.
When it comes to deaths from Covid a fully vaccinated 80-year-old has a similar risk to an unvaccinated 50-year-old.
Future twists and turns in the pandemic may yet change the mathematics. Having a large wave of infections with roughly half the UK population vaccinated provides ripe conditions for a variant that can better evade the protection of vaccines.
Another concern is how soon vaccines wear off. Several studies have shown that antibody levels fall over time, but it is unclear what the declines mean for immunity and protection against infection, hospitalisation and death. The answer could become clear in the months ahead. As hospitals brace for another wave of patients, health officials will watch closely to see if more beds are needed for those jabbed first.