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The cases are already starting to emerge.
When Colin Horseman, 85, was admitted to Doncaster Royal Infirmary at the end of December, it was with suspected kidney infection. But soon after, he caught Covid-19 – at the time, around one in four people hospitalized with the virus had contracted 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, but no less tragic for her. After all, at least 84,767 people have died of 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 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 before his death.
In fact, most vaccines require booster doses to work.
Take the MMR vaccine – measles, mumps and rubella – which is given to babies all over the world to prevent these deadly childhood infections. About 40% of people who received only one dose are unprotected from all three viruses, compared to 4% of those who had their second. People in the first group are four times more likely to catch measles than those in the second – and there have been outbreaks in places where a high proportion of people have not completed the full MMR immunization schedule.
“The reason people love boosters so much and consider them so vital is that they kind of send you into this whole other mode of fine-tuning your immune response,” says Danny Altmann, 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 of all, plasma B cells, which mainly focus on making antibodies. Unfortunately, this type of cell is short lived, so while your body can swim in antibodies in just a few weeks, without the second injection, this is often followed by a rapid decline.
Then there are the T cells, each of which is specifically designed to identify a particular pathogen and kill it. Some of these, memory T cells, can linger in the body for decades until they hit their target – which means immunity to vaccines or infections can sometimes last a lifetime. life. Most importantly, you usually won’t have much of this cell type until the second meeting.
The booster dose is a way to re-expose the body to antigens – the molecules on pathogens that trigger the immune system – to initiate the second part of the response. “You threw all this fancy stuff,” says Altmann. “So once you’ve had your boost you’ll have a higher frequency of memory T cells and to some extent for the size of the memory B cell pool you will have. They will also produce better quality antibodies. .. “
On a second exposure to the same vaccine or pathogen, the remaining B cells from before are able to divide rapidly and create a threatening crowd of offspring, leading to a second spike in the amount of circulating antibody.
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