Tom Leslie
A joint university study backs up the idea of giving single vaccine doses to those who are most at risk.
The University of Oxford, in partnership with the universities of Liverpool, Sheffield, Cambridge, Newcastle, and Birmingham, has conducted a study, referred to as PITCH (Protective Immunity from T-cells in Healthcare Workers), on a cohort of 237 healthcare staff.
PITCH aims to uncover more about protective immunity against COVID-19, which covers immunity caused either by vaccination or natural exposure (i.e. catching the virus out in the world). A major target of their research is T-cell mediated immunity. T-cells are an essential component of viral immunity, however, their contribution to the immune response is usually more challenging to quantify than that of antibodies. In the past, this has led to an underappreciation of the role that T-cells play.
In the PITCH report, 113 of 237 healthcare staff had previously been infected with COVID-19, and the remaining 124 were infection naive (i.e. had never been infected). The researchers vaccinated both groups with the Pfizer vaccine, taking blood samples from these participants before and after vaccination to assess different aspects of their immune response. This assessment included an evaluation of both their antibody and T-cell levels.
Previous studies have shown that protective immunity against severe COVID-19 lasts for at least five months. These studies were carried out on unvaccinated individuals who contracted the virus by natural exposure. Compared to immunity by natural exposure, the PITCH study reports equivalent or higher antibody and T-cell responses in infection-naive individuals after receiving one dose of the Pfizer vaccine.
These data indicate that one dose of the Pfizer vaccine protects against severe disease to a similar extent as would be provided by natural exposure. The report’s authors interpret this result as supportive evidence for delaying the rollout of second vaccine doses. Instead, they suggest that more single injections could be provided to high-risk groups.
The researchers have also discovered that vaccination broadens T-cell responses in previously infected people, which could improve their immune activity against new SARS-CoV-2 variants. Increased response breadth suggests that the T-cells could work against different regions of the spike protein, a significant target for the immune system.
Study author Susanna Dunachie, NIHR Global Research Professor at the Nuffield Department of Medicine, says, ‘In immunology, this [the expansion of target areas] is a positive thing because it means you’re more likely to retain protection against new virus mutations’.
Photo by Diana Polekhina on Unsplash
- Angyal, A. et al. T-Cell and Antibody Responses to First BNT162b2 Vaccine Dose in Previously SARS-CoV-2-Infected and Infection-Naive UK Healthcare Workers: A Multicentre, Prospective, Observational Cohort Study. (2021) doi:10.2139/ssrn.3812375
- Hall, V. et al. Do antibody positive healthcare workers have lower SARS-CoV-2 infection rates than antibody negative healthcare workers? Large multicentre prospective cohort study (the SIREN study), England: June to November 2020. bioRxiv (2021) doi:10.1101/2021.01.13.21249642
