People who were on the coronavirus shielding list have lower levels of protection against becoming seriously ill as a result of the virus, even after two doses of vaccine, research has found.
The study, led by Public Health Scotland and supported by the University of Edinburgh, was published as booster jabs began being rolled out to Scots aged over the age of 50.
It found those who were classed as clinically extremely vulnerable had 66% protection against severe illness after two vaccine doses.
That compares to a 93% protection in those without any high-risk conditions who have been double dosed.
Researchers said they hoped a third booster vaccine would increase protection levels further for those who had been asked to shield.
Of more than 3.5 million people who have had two vaccine doses in Scotland, the study found there were just 330 cases of severe Covid-19.
Almost half of these were in people whose health conditions meant they were classed as “extremely vulnerable” while most of the remainder were in people with more moderate risk conditions.
Professor Helen Colhoun, of the University of Edinburgh, said: “It is clear that getting vaccinated with two doses is an effective way of reducing the risk of getting severely ill from Covid-19.
“However, our study did show that people who were previously asked to shield as a result of being clinically extremely vulnerable to Covid-19 did have lower protection after two doses than those without their conditions.
“We found that out of over 3.5 million people who have had two vaccine doses in Scotland up to September 2, 2021, there were just 330 cases of severe Covid-19. Almost half of these are in people designated as extremely vulnerable and most of the remainder have been in people with moderate risk conditions.
“The fact that we see an increase in protection from the first to the second dose gives hope that a third dose might increase protection further.”
Dr Nicholas Phin, director of public health science at Public Health Scotland, said: “The findings of this study confirm that all the vaccines approved for use in the UK continue to be highly effective at reducing severe illness and death from Covid-19.
“Whilst those who are clinically extremely vulnerable get, on average, a substantial level of protection to Covid-19, it will vary from person to person and by the nature of their vulnerability.
“We therefore welcome the JCVI advice and the subsequent rollout of the programme that prioritises a third dose for those who are known to be at most-risk from Covid-19.”
He added: “If you are contacted to receive a third dose then please do take the opportunity to bolster your protection against Covid-19. If you have not had any doses of a Covid-19 vaccine yet, you can protect yourself and others by registering online or finding your nearest drop-in vaccination centre via the NHS Inform website.”