Cases are already beginning to appear.
When Colin Horseman, 85, was hospitalized at Doncaster Royal Infirmary in late December, it was a suspected kidney infection. But it wasn’t long before he caught Covid-19 – at that time, about one in four people in the hospital had the virus. 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 quite typical, though no less tragic for her. 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 to receive the second dose two days before his death.
In fact, most vaccines require booster doses to work.
Take the MMR vaccine – measles, mumps and rubella – which is given to children around the world to prevent these deadly infections in childhood. About 40% of people who received a single dose are not protected by all three viruses, compared to 4% of those who had their second. People in the first group are four times more likely to get 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 program.
“The reason people are so eager for boosters and find them so vital is that I’m kind of sending you into this other kind of fine-tuning your immune response,” says Danny Altmann, a professor of immunology at Imperial College London.
How booster vaccines work
When the immune system first encounters a vaccine, it activates two important types of white blood cells. First and foremost are plasma B cells, which focus primarily on antibody production. Unfortunately, this type of cell is short-lived, so although your body can swim in antibodies in just a few weeks without a second blow, this is often followed by a rapid decline.
Then there are the T cells, each of which is specially adapted to identify a specific pathogen and kill it. Some of these, memory T cells, are able to stay in the body for decades until they stumble upon their target – which means that immunity to vaccines or infections can sometimes last a lifetime. But essentially, you won’t have much of this cell type until the second date.
The booster dose is a way to re-expose the body to antigens – the molecules on the pathogens that trigger the immune system – to initiate the second part of the response. “You kicked in all these fancy things,” says Altmann. “So, once you have the impulse, you will have a higher frequency of memory T cells and, to some extent, for the size of the group of memory B cells that you will have. . “
Upon second exposure to the same vaccine or pathogen, the remaining B cells are able to divide rapidly and create a threatening multitude of offspring, leading to a second increase in the amount of antibodies circulating.