Two vaccines and a previous infection provides 20 per cent more protection compared to recovering from the virus alone, a government study suggests.

The SIREN study, led by researchers at the Universities of Oxford and Cambridge, and funded by the UK Health Security Agency (UKHSA), aims to understand how long immunity lasts from prior infection.

The latest findings, which are not yet peer reviewed, show two doses of a Covid vaccine on top of prior infection “significantly reduces” both symptomatic and asymptomatic Covid infection, compared to previous infection alone.

Dr Susan Hopkins, Chief Medical Advisor of the UKHSA who led the study, shared the findings after the debate around protection from prior-infection was raised by Dr Steve James, a consultant anaesthetist at King’s College Hospital (KCH), London.

Dr James told Sajid Javid, the Health Secretary, during a televised visit to the hospital that “the science is not strong enough” to warrant mandatory jabs for frontline NHS workers, and that he had acquired immunity through infection.

From April, Covid vaccinations are mandatory for frontline NHS workers.

The SIREN study shows those who are double jabbed have significantly more protection a year after infection.

More than 35,000 healthcare workers were included in the study, which tracked participants between December 2020 and September 2021.

Omicron data being analysed

The findings show unvaccinated persons who had Covid developed 85 per cent protection against infection three to nine months after, but this dropped 73 per cent protection more than 15 months after infection.

However, double vaccinated people who tested positive three to nine months prior had 91 per cent protection, and more than 15 months after infection they still had over 90 per cent protection.

“In this pre-print, which is under peer review, we demonstrate that two doses of vaccination on top of prior infection significantly reduces both asymptomatic [and] symptomatic infection compared to infection alone,” Dr Hopkins said.

She added the research group is beginning to analyse data from the current omicron wave.

“The consensus from immunologists [and] infection experts is, getting a boost to your immunity from vaccination on top of prior infection will reduce asymptomatic [and] symptomatic infection [and therefore] reducing transmission,” she said.

Immunity by previous infection ‘wanes’

The authors of the study concluded protection from infection-acquired immunity showed “evidence of waning” in unvaccinated persons at follow-up, but remained “consistently over 90 per cent in those who received two doses of vaccine, even in those infected over 15-months ago”.

Separately, the Royal College of Anaesthetists and the Faculty of Intensive Care Medicine said they encourage all members and other NHS staff to take up the offer of a vaccine.

“We note that the overwhelming majority of our members have been vaccinated regardless of prior infection, in line with the scientific evidence,” the two bodies said in a joint statement earlier this week.

“Collectively, we need to listen to and acknowledge the concerns of those healthcare workers who have chosen so far not to be vaccinated, so that they are supported to make the best health choices for their patients, their families and themselves.    

“A comparison of the protection from prior infection and protection via vaccination is not a matter on which RCoA nor FICM has any expertise. However, we note the advice of experts in epidemiology and virology that the immunity gained from vaccination is stronger and longer lasting than that from infection.”