Cases are already beginning to emerge.
When Colin Horseman, 85, was admitted to Doncaster Royal Infirmary in late December, it was on suspicion of kidney infection. But soon after he took Covid-19; at that time, approximately one in four people hospitalized with the virus had acquired it there. He presented with severe symptoms and finally put on a ventilator. A few days later, he died.
At first glance, Horseman’s situation may seem quite typical, though no less tragic to her. After all, at least 84,767 people have succumbed to the disease in the UK alone at the time of writing. But, as her son recently explained in a local newspaper, less than three weeks earlier she 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 function.
Get the measles, mumps, and rubella vaccine, which is given to babies around the world to prevent these deadly childhood infections. About 40% of people who have received only one dose are not protected from the three viruses, compared to 4% of those who have had the second. People in the first group are four times more likely to get 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 vaccination program.
“The reason people are so interested in boosters and consider them so vital is that they send you into this other kind of way of tuning your immune response,” says Danny Altmann, professor of immunology at ‘Imperial College London.
How booster vaccines work
When the immune system first comes across a vaccine, it activates two important types of white blood cells. First, there are plasma B cells, which focus primarily on the production of antibodies. Unfortunately, this type of cell is short-lived, so although the body can swim in antibodies in a few weeks, without the second shot there is often a rapid decline.
Then there are the T cells, each of which is specifically adapted to identify a specific pathogen and kill it. Some of these, memory T cells, can persist in the body for decades until they hit their target, meaning immunity to vaccines or infections can sometimes last a lifetime. But most of all, you won’t usually have many of these cells until the second meeting.
The booster dose is a way to re-expose the body to antigens (the molecules of the pathogens that trigger the immune system) to initiate the second part of the response. “You’ve suffered all these luxury things,” Altmann says. “So once you have your impulse, you’ll have a higher frequency of memory T cells and the same goes for the size of the set of memory B cells you’ll have. They’ll also make higher quality antibodies. . “
On second exposure to the same vaccine or pathogen, the remaining B cells can quickly divide and create an endangered multitude of offspring, causing a second increase in the amount of antibodies circulating.