Doherty Institute’s ‘surprising’ find in how immune system fights Covid post vaccine

New research has probed just how quickly the immune system jumped into gear to fight Covid in those who have been jabbed.

A unique investigation of how the immune system responds to Covid-19 in people who have been vaccinated confirms it reacts ‘surprisingly’ quickly to fight infection.

A unique investigation of how the immune system responds to Covid-19 in people who have been vaccinated confirms it reacts “surprisingly” quickly to fight infection and has a long memory.

The research, by a team from the Peter Doherty Institute for Infection and Immunity and the University of Melbourne, found that the immune response established from Covid-19 vaccines was ready and able to respond to a new infection.

The Melbourne researchers were among the first in the world to take samples early after people became sick from Covid-19.

The samples were from 23 Victorians who had been immunised and later became infected with Covid-19.

A health worker prepares a dose of the Pfizer-BioNTech vaccine.

In this group the infections were mild to moderate and no one required hospitalisation.

University of Melbourne’s Dr Marios Koutsakos, a Research Fellow at the Doherty Institute, led the study and found T cells – the immune system’s first responders to infection – remembered and rapidly responded to the virus because they had been primed to fight the infection by the vaccines.

What makes the study unique, Dr Koutsakos says, is that the researchers had blood and nasal samples from early after infection.

“This means we have both immunology information and information about the virus,” he said.

Senior author Dr Jennifer Juno from the Doherty Institute said the team was excited to see that, even one day after the symptoms started T cells had already detected the infection, were activated and started to increase in numbers to fight infection.

Dr Koutsakos said this swift T cell response was a surprise.

“In a good way,” he said.

Melbourne researchers were among the first in the world to take samples of Covid.

“We weren’t sure how quickly the T cells would recall, react and respond to the virus as there are not a lot of cohorts worldwide that have this information.

“What we found is the immune system is doing what it is supposed to do after vaccination.”

The study included people who had received two or three vaccines and later were infected with the Delta or Omicron variants and highlighted that multiple vaccinations produced a durable T cell response.

Of the group on the cohort, seven were followed the entire course of the pandemic – almost 900 days.

The researchers said this provided a novel insight into the long-term maintenance and recall of T cell immunity.

Next they want to study if there are similar links of response to disease severity.

The results have been published online in Immunity.