As one of the largest vaccine rollouts in history continues, the debate has continued as to whether recipients require two doses, as the manufacturers recommend, or just one single dose – a tactic many countries have now employed to spread their doses widely across the population.  

Now, a new preprint study led by Sheffield and Oxford Universities has found that 99% of health workers that received a single dose of the Pfizer vaccine generated a robust immune response, generating defensive immune cells ready to fight off the virus. The researchers also discovered that people that had a history of past COVID-19 infection showed an immune response over six times larger than that of people who have never had the virus, suggesting anyone who has previously contracted COVID-19 may see improved protection following the vaccine. 

Their preprint results, yet to be peer-reviewed, are to be published in The Lancet. 

Whilst the results suggest strong protection from just one dose, the UK Government still urges everyone to receive their full course of two doses as soon as it is offered. 

“These findings from the PITCH study are crucial to increasing our understanding of the immune response to COVID-19 and how the Pfizer vaccine is working to protect people across the UK already,” said Health Minister Lord Bethell, in a statement. 

“I urge everyone to come forward to be vaccinated when invited and to take up both doses of the vaccine as both are vital to ensuring long-term protection from COVID-19.” 

The study involved 237 healthcare workers, who were among the first to receive a vaccine in the UK’s multi-step plan, with 216 having received one dose and 21 receiving 2 doses. Running across a study period of two months between December 9 and February 9, researchers analyzed blood samples from these health workers to assess their immune response to the vaccine, and whether past COVID-19 infection had an effect on this response. 

Delving into the results, the researchers noted that 99% of people in the single-dose category had strong T-cell and antibody responses. T-cells are integral in the recognition and destruction of invading viruses, and higher levels of specific T-cells and antibodies that target the SARS-CoV-2 spike protein is promising for the success of vaccination. Alongside that, they found that in people that had previously contracted COVID-19, T-cell response after just one dose was equivalent to those who had not had COVID-19 before but had received 2 vaccine doses. Compared to people who had received just one dose and had not previously had COVID-19, people with past infection showed a 6.8-times higher antibody response and a 5.9-times higher T-cell response. 

The study is an early cohort study involving a small sample size, specifically in the two-dose category, so acts only as preliminary data. However, it provides promising results for recipients of the Pfizer vaccine. 

“Our study is one of the largest and most comprehensive accounts of the immune response to one dose of Pfizer/BioNTech vaccine comparing previously infected and infection-naive individuals. Our results demonstrate that T cell and antibody responses induced by natural infection are boosted significantly by a single dose of vaccine. While the response to a single dose was lower in infection-naïve individuals, it was still equivalent or better than the immunity in previously infected individuals before it is boosted by vaccination.” said Dr Thushan de Silva, study author, in a statement.