Two doses of vaccine offer same protection from COVID as prior infection, study finds

Two doses of either the Pfizer or Oxford-AstraZeneca vaccine offer similar protection against symptomatic SARS-CoV-2 infection to that coming from natural immunity after infection, an ongoing study of healthcare workers has found.

None of the 1,456 healthcare workers at Oxford University Hospitals (OUH) NHS Foundation Trust who had received two vaccines had a symptomatic infection when followed up more than 14 days after their second vaccination. The same high level of protection was seen in unvaccinated healthcare workers who had contracted COVID-19 naturally; they had 98% fewer symptomatic infections than unvaccinated individuals who had not been infected before. 

Most of the healthcare workers studied had only received one vaccine to date. Protection against symptomatic infection was lower – at 67% - after a first dose of vaccine - received by 11,023 hospital staff.

The findings were the latest data from ongoing analysis of symptomatic and asymptomatic staff testing for SARS-CoV-2 at OUH’s four hospitals and associated facilities. In total, 13,109 healthcare workers have participated.

Of these, 8,285 have received the Pfizer-BioNTech vaccine (1,407 of them two doses) and 2,738 the Oxford-AstraZeneca vaccine (49 of them receiving both doses).

The study was published on the MedRxiv pre-print server. It has been carried out jointly by researchers and clinicians from OUH and a number of University of Oxford departments, including the Nuffield Department of Medicine and the Big Data Institute, with support from the NIHR Oxford Biomedical Research Centre.

Dr Katie Jeffery, OUH Director Infection Prevention and Control, said: “We are grateful to the thousands of staff who work at OUH’s hospitals who have taken part in the testing programme. It has provided a rich source of data that continues to shed light on the nature of this new virus and how immunity to it is conferred.

“In this case it is significant that two doses of the vaccines offer similar levels of protection to natural immunity, and that we saw no symptomatic infections among those staff who had had two vaccine doses. Data from studies such as this are important as they provide information which may feed into national policy. It also highlights that healthcare workers and other groups at increased risk of infection should take up second vaccines as soon as these are available,” she said.

By using viral sequencing, the Oxford team found that there was no evidence that either vaccine or natural infection provided less protection against the new B.1.1.7 “Kent” strain of the virus.

The study also found that rate of positive PCR tests with or without symptoms were lower after vaccination and previous infection, suggesting that both vaccination and previous infection are likely to reduce onward transmission, and even when people did get infected after a previous infection there was evidence that the amount of virus present was reduced, making transmission less likely.

“These findings suggest that evidence of vaccination or previous infection with detectable antibodies could potentially be used to develop a more personalised approach to easing of lockdown restrictions,” said one of the authors on the paper, Professor David Eyre of the University of Oxford’s Nuffield Department of Population Health.

Earlier work from the team, published in June 2020, revealed the different levels of risk faced by healthcare workers dealing with the first wave of the COVID-19 pandemic. 

Rigorous measures have been taken since to prevent the spread of SARS-CoV-2 in hospital, including universal PPE use, support for social distancing and ensuring there is mitigation in place for poorly ventilated areas. All staff are risk assessed for Covid-19, and offered vaccination.  

Prof Meghana Pandit, OUH’s Chief Medical Officer said: “OUH has an extensive staff testing programme, whose primary aim is to keep our staff and patients safe; we continue to offer our asymptomatic and symptomatic staff PCR testing and have introduced twice-weekly lateral flow testing, which is available to all staff. The information this ongoing testing programme has produced has proved valuable for our understanding of the prevalence of the virus and immunity to it.

“This current study has shown that healthcare workers caring for patients with COVID-19 during the second wave were still at increased risk of getting infected, but not by so much as in the first wave. Nurses, healthcare assistants and Asian staff also remained at higher risk of infection. The study shows we have made good progress in protecting staff working in hospitals, but also that more can be done. We are actively looking at what further measures we can put in place to offer our staff the best protection possible.”

OUH Chief Executive Dr Bruno Holthof added: “Since the pandemic began, our Trust and the University of Oxford have worked closely together to develop and deliver a reliable and comprehensive testing programme to improve patient care, staff safety and our understanding of the virus.”

“I’d like to thank the Department of Health and Social Care for helping to fund the staff testing programme, the thousands of staff who have participated in the programme allowing us to achieve meaningful findings, and the infectious diseases and microbiology teams, research nurses and medical students who have worked tirelessly to take these samples. It has been a fantastic team effort.