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Two new papers from scientists in the Nuffield Department of Medicine and other University of Oxford institutions have shown how the immune system reacts differently depending on the length of interval between vaccine doses.

Medical sciences researcher working in a laboratory

Adjusting when a vaccine booster dose is given can have a major effect on how immune responses are triggered, according to new research from scientists at the Pandemic Sciences Institute (PSI) and Experimental Medicine Division.

The team of scientists, which also included the Oxford Vaccine Group, studied a group of healthcare workers who received two COVID-19 vaccines during the initial vaccine rollout – the Pfizer BNT162b2 mRNA vaccine and the Oxford/AstraZeneca ChAdOx1 nCoV-19 vaccine.

The researchers explored the immune signals occurring within one day after the first vaccine dose and the second booster dose, to understand how vaccination is initially triggering the immune system. They specifically focused on T cell immunity, which works together with antibodies to protect people against viruses.

Despite extensive studies of these vaccines, gaps in understanding around early immune responses and T cell immunity still exist. 

Researchers found that for the Pfizer mRNA vaccine, the booster dose more strongly turned on the early immune response than the first dose, and this was linked to the activation of so-called ‘unconventional’ T cells in the blood.

In contrast, the Oxford/AstraZeneca vaccine triggered these unconventional cells very strongly after the first dose. These specialised cells pick up early signals and act as powerful ‘amplifiers’ to create a much bigger early immune reaction. This early immune activation is what contributes to early side effects that individuals experience after vaccination.

By extending the interval between mRNA vaccine doses (from around 3 weeks to 3 months), this early reaction of ‘unconventional’ T cells was reduced, and this was linked to a reduction in the early symptoms the recipients experienced (reactogenicity) after the booster.  

In parallel, the team of scientists also studied the impact of the different vaccines on the protective immune response they induced against the virus. The team used a new test that was able to pick up many different types of T cell responding to the vaccine. 

 

Read the full story on the Nuffield Department of Medicine website.