The study, involving experts from Newcastle University, shows that one dose of the Pfizer vaccine generated a robust immune response against Covid-19 in all participants.

Findings highlight that a single dose of the vaccine protects against severe disease and supports the delay of the second dose in order to provide as much protection as quickly as possible for higher-risk groups.

PITCH study

The PITCH study examines how the immune system responds to Covid-19 after one dose of the Pfizer vaccine among individuals with and without a previous history of Covid-19 infection.

Between 9th December 2020 and 9th February 2021, researchers from the Universities of Newcastle, Sheffield, Oxford, Liverpool and Birmingham analysed blood samples from 237 healthcare workers to understand their T cell and antibody responses following vaccination.

It found people who had previously been infected with Covid-19 showed higher T cell and antibody responses after one dose of the vaccine compared with people who had never had COVID-19 before and had one dose of the vaccine.

However, the researchers also discovered that among previously infected individuals, the T cell response expanded after vaccination to recognise more regions of the Covid-19 spike protein - the protein that attacks the immune system and causes severe disease. 

This means vaccination provides a better immune response to COVID-19, including against variants, than the immune response from natural infection.

Dr Christopher Duncan, from Newcastle University's Faculty of Medical Sciences and Honorary Consultant in Infectious Diseases at Newcastle upon Tyne Hospitals NHS Foundation Trust, said: "We are proud in Newcastle to have made a leading contribution to this important study, the largest of its kind, which sheds new light on the T cell response to coronavirus vaccination.  

“It provides important reassurance that vaccination induces a robust immune response in all recipients. 

"The study shows the value of a collaborative approach to research during a pandemic, reflecting a huge team effort by multiple academic and NHS research partners. 

"I especially want to thank all the volunteers in the Newcastle upon Tyne Hospitals NHS Foundation Trust as well as the SIREN research team for supporting this work."   

The first dose of both the Pfizer and AstraZeneca vaccine offer good levels of protection, but to get maximum protection it is vital everyone gets a second dose when invited. 

Two doses of the vaccine will provide longer-lasting protection from the virus. Everyone must continue to follow the rules – remembering hands, face, space – even after vaccination as it is still possible to pass the virus on to others.

Main findings

Key findings from the PITCH study:

• T cell response was just as strong among those who had never had Covid-19 before and received two vaccine doses, as those who had previously had Covid-19 and one vaccine dose
•  Antibody and T cell responses were at a similar or higher level among those who received one dose of the vaccine but had never had Covid-19 before, compared to those who had previously been infected but not been vaccinated
• After one dose of the vaccine, participants who had previous Covid-19 infection showed higher antibody and T cell responses compared with people who had not been infected before, with antibody responses approximately 6.8 times higher and T cell responses approximately 5.9 times higher
• High antibody responses in individuals who had previously been infected and vaccinated may protect against some variants of concern
• Among those who had not had previous Covid-19 infection and received two vaccine doses, T cell responses were as strong as those observed in participants who had previously had Covid-19 and one vaccine dose
• Antibody levels were still significantly lower than those observed in participants who previously had Covid-19 after one vaccine dose.

An effective vaccine is one that saves lives and reduces hospitalisations. Both the Pfizer and Oxford-AstraZeneca vaccines are highly effective in reducing Covid-19 infections among older people aged 70 years and over. 

In the over 80s, data suggest that a single dose of either vaccine is more than 80% effective at preventing hospitalisation, around three to four weeks after the jab.

Dr Rebecca Payne, from Newcastle University's Faculty of Medical Sciences, said: "We are especially humbled by the resilience and support of the NHS healthcare workers enrolled in the SIREN study, who regularly gift samples to this important research whilst also dealing with the physical and mental challenges of supporting the NHS during the pandemic."

Further research is now needed to understand the immune responses over the longer term and what it means for protection against Covid-19 in the real world.