A new study from the UK Coronavirus Immunology Consortium, published in Nature Communications, suggests that receiving two doses of the Pfizer/BioNTech vaccine induces T cell responses (an important part of the immune response) that are effective against the recent B.1.1.7 (Kent) and B.1.351 (South African) variants.
While the rollout of COVID-19 vaccines is a positive step in defeating the pandemic, the appearance of new variants of SARS-CoV-2, the virus that causes COVID-19, 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. This is important as the immune system learns to recognise parts of the virus like the Spike protein following vaccination, and some of the variants have significant changes to regions like this. The Spike protein sticks out and helps the virus enter cells, so it is a good region to target with vaccines. If its structure changes too much, it might be harder for the immune system to recognise the new variants, and it may be less able to launch a quick and effective defensive response following vaccination.
The B.1.1.7 (Kent) variant of SARS-CoV-2 has become the dominant variant circulating in the UK in recent months; a much higher proportion of new cases are due to this variant. A few cases of the B.1.351 (South African) variant have also been found in the UK more recently. It is therefore important to study the immune response generated following vaccination to these new variants, and ensure that they provide effective protection against them.
For this study, Professors Eleanor Barnes, Susanna Dunachie and Paul Klenerman from Oxford University 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). They also collected samples from patients with severe COVID-19, as well as 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 (B.1.1.7 and B.1.351).
T cells, a key component of your immune system, learn to recognise specific features of viruses in order to protect the body. In the case of COVID-19, immunologists have found that T cells learn to recognise parts of the Spike protein on SARS-CoV-2, the virus that causes COVID-19. They found that T cells that target the Spike protein 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, meaning that these T cells are able to recognise both the original virus and the newer 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.
Antibodies are another line of defence against viruses. When we are exposed to a new virus or pathogen, the body produces antibodies that target specific regions of it in order to neutralise it, in a similar way to how T cells recognise specific regions. Professors William James and Miles Carroll, who also worked on the project, found that antibody responses to SARS-CoV-2 were high following two doses of the Pfizer vaccine, but they had less capacity to neutralise the B.1.351 (South African). However, the researchers state that this is likely to still be at a protective level. After only one dose of the vaccine, antibodies were not able to neutralise the South African variant in a lab setting, which reinforces the importance of receiving both doses of the vaccine.
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. More research is now needed to assess the T cell response to the different variants after one vaccine dose.