During Covid, some patients seemed to have a better response to vaccination than others and we never knew why. Well, Cambridge scientists have now identified a “signature” in blood that could help predict how well someone will be protected by vaccines.

The discovery may explain why, even among vulnerable patient groups, some have better responses to vaccines than others. They’re better protected. Many studies have shown Covid vaccines are less effective in people with weakened immune systems, but that isn’t always the case.

Vaccination primes the immune system to look for, and get rid of, invaders, such as viruses and bacteria. In part, this involves stimulating the production of antibodies uniquely programmed to identify a particular invader.

These antibodies are produced by a type of immune cell known as a B cell. One type of these is known as an age-associated B cell (ABC). While fewer than one in 20 of a healthy person’s B cells is an ABC, the proportion gradually increases as we get older.

Certain people with weakened immune systems accumulate ABCs faster than average. A team from Cambridge University, led by Dr James Thaventhiran, has examined ABCs from very different patient groups – first, people with an inherited condition that impairs the activity of their immune systems, and second, cancer patients taking immunotherapy drugs – as well as from healthy individuals.

Emily Horner, from Dr Thaventhiran’s team, explained the aim of the research. “By looking at patients’ B cells, we hoped to learn how we could stratify vulnerable patients – in other words, work out whether some patients were at greater risk from infection, even after vaccination, than others.”

The researchers measured the relative proportion of ABCs compared to healthy B cells, and their activity. In tandem with Dr Nicholas Matheson from Cambridge University, they tested how these numbers influence the ability of a vaccinated person’s immune system to neutralise a live Covid virus.

Dr Juan Carlos Yam-Puc, also from Cambridge University, said: “The greater the proportion of ABCs in an individual’s blood, the less effective that individual was post-vaccination at neutralising the virus.”

Dr Pehuen Pereyra Gerber, from Dr Matheson’s lab, added: “Looking at blood levels of ABCs could tell us that person A should respond well to a vaccine, while person B might need a stronger vaccine or to be prioritised to receive a booster.”

Dr Thaventhiran added: “Ultimately, this research could lead to the development of a clinical test to predict vaccine efficacy for immunodeficient patients, and for the population more generally.”

What a huge step forward.