Pfizer vaccine induces robust T cell responses against new SARS-CoV-2 variants

12th February 2021

3D illustration of SARS -CoV- 2 virusT cell responses to the spike protein of SARS-CoV-2 are still effective against the recent B1.1.7 (Kent) and B1.351 (South African) variants following two doses of the Pfizer/BioNTech COVID-19 vaccine, a new preprint from researchers in the UK Coronavirus Immunology Consortium suggests. The work led by researchers from the University of Oxford is the first to look at the changes in T cell responses, alongside antibody responses to the new variant viruses after vaccination. Antibody responses were also high following two doses, however with less capacity to neutralise the recent variants. After only one dose of the vaccine, antibodies were not able to neutralise the B1.351 variant in a lab setting.

While the rollout of COVID-19 vaccines is a positive step in defeating the pandemic, the emergence of new variants of SARS-CoV-2 remains a cause for concern. It is currently unclear what level of protection vaccines are able to provide against newer variants of the virus, as they were designed based on the original virus circulating in Spring 2020 and some of the variants have significant changes to binding sites such as the spike protein. The B1.1.7 (Kent) variant has become the dominant variant circulating in the UK in recent months, displacing the original virus of the first wave. A few cases of the B1.351 (South African) variant have also been found in the UK more recently. It is therefore important to assess the immune response generated following vaccination to these new variants.

For this study, Professors Eleanor Barnes, Susanna Dunachie and Paul Klenerman, led a team who collected blood samples from healthcare workers not known to have had a previous COVID-19 infection and those recently vaccinated with the Pfizer/BioNTech COVID-19 vaccine (two doses, 18-28 days apart), as well as patients with severe COVID-19 and healthcare workers with asymptomatic or mild COVID-19. Blood samples were taken immediately before vaccination, and 7-17 days after a second dose of vaccine. The researchers tested antibody and T cell responses to the original strain of SARS-CoV-2 and compared this to responses to the two new variants (B1.1.7 and B1.351). 

They found that T cells that target the spike protein on SARS-CoV-2 were generated at a high level against all variants tested following two doses of the vaccine. These T cells appear to target regions of the spike protein that are conserved between all variants. This is the first study to look at this effect and it suggests that effective T cell responses may be maintained at a good level against the new variants.

Professors William James and Miles Carroll, who also worked on the project, found that antibody responses were high after two vaccine doses, and antibodies were able to neutralise all variants. This effect was less pronounced for the B1.351 variant; however the researchers state that this is likely to still be at a protective level. After only one dose of the vaccine, antibody responses were lower and were unable to neutralise the B1.351 variant in the lab. This is one of the first studies to assess neutralisation of all of the variants using live virus in the lab.  This study is part of the PITCH Consortium funded by the Department of Health and Social Care. More research is now needed to assess the T cell response to the different variants after one vaccine dose. 

The results emphasise the importance of monitoring vaccine effectiveness against new SARS-CoV-2 strains and the urgent need to quickly deploy effective vaccine strategies to provide protection to the public against these SARS-CoV-2 variants. 

Professor Eleanor Barnes, UK-CIC researcher, Professor of Hepatology and Experimental Medicine at the University of Oxford, said:

“Understanding how effective current COVID-19 vaccines are against new virus variants is crucial to being able to protect the population from contracting COVID-19.  Our findings are reassuring in that they show that good T cell responses are still generated against the new variants of SARS-CoV-2 following two doses of the Pfizer/BioNTech vaccine. This is encouraging news especially as the B1.1.7 variant now accounts for most COVID-19 cases in the UK. We believe this is the first study to look at this and it is a significant step forward in understanding how this particular vaccine can induce a protective immune response to the virus.”

Details on the full preprint can be found here.


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