James' World 2

The cases are already beginning to emerge.

When 85-year-old Colin Horseman was admitted to Doncaster Royal Infirmary in late December, it was for a suspected kidney infection. But not long afterwards he caught Covid-19 – at the time, roughly one in four people in hospital with the virus had acquired it there. He developed severe symptoms and was eventually put on a ventilator. A few days later, he died.

At first glance, Horseman’s situation may seem fairly typical, though no less tragic for it. After all, at least 84,767 people have now succumbed to the disease in the UK alone at the time of writing. But, as his son recently explained in a local newspaper, less than three weeks earlier he had been among the first people in the world to receive the initial dose of a Covid-19 vaccine – the Pfizer-BioNTech version. He was due to receive the second dose two days prior to his death.

In fact, most vaccines require booster doses to work.

Take the MMR – measles, mumps and rubella – vaccine, which is given to babies around the world to prevent these deadly childhood infections. Around 40% of people who have received just one dose are not protected from all three viruses, compared to 4% of those who have had their second. People in the former group are four times more likely to catch measles than those in the latter – and there have been outbreaks in places where a high proportion of people have not completed the full MMR vaccination schedule.  

“The reason that people are so keen on boosters and consider them so vital is that they kind of send you into this whole other kind of fine-tuning mode of your immune response,” says Danny Altmann, professor of immunology at Imperial College London.