Elderly Brits vaccinated with AstraZeneca are less likely to have Covid antibodies than those who had Pfizer, a study suggests.
The major research by Imperial College London indicates that the Oxford jab may be slightly weaker than its American-German counterpart.
Around 85 per cent of elderly people who had two AZ vaccines had detectable antibodies, compared to 98 per cent of those who had both doses of Pfizer.
Experts have said the findings of the study are not surprising as Astrazeneca is made from a weakened version of a common cold virus.
Unlike AZ, Pfizer is a new type of jab called an RNA vaccine, which uses a tiny fragment of Covid's genetic code that the immune system recognises as foreign and fights.
Scientists behind the study have highlighted the importance of getting both doses of the jab for the best chance of developing immunity - regardless of which of the approved manufacturers they come from.
The level of protection offered by AZ is still strong and the jab has been proven to be effective at preventing severe illness and death.
The study report says: "Following two doses of Pfizer-BioNTech vaccine, antibody positivity was 100 per cent at all ages except 80 years and older when it was 97.8 per cent.
"For AstraZeneca positivity was over 90 per cent up to age 69, and then 89.2 per cent in 70-79 year olds and 83.6 per cent in those aged 80 and over.
"Following a single dose of Pfizer-BioNTech positivity ranged from 100.0 per cent in those aged 18-29 to 32.2 per cent in those aged 70-79 years.
"For AstraZeneca this was 72.2 per cent in the youngest and 46.2 per cent (40.0-52.7) in the oldest age group."
Prof Graham Cooke, Professor of Infectious Diseases, Imperial College London, said: "It's variable as to how many antibodies after one dose of AstraZeneca or Pfizer but second dose overrides that with good response.
"Both of the main vaccines require that second dose to neutralise the virus properly."
All adults over 18 can now get their second vaccine eight weeks after their first now.
Officials and medical experts have urged Brits to get both doses as Freedom Day as they prepare for the highly anticipated Freedom Day on Monday.
Cases are expected to surge after the final stage of lockdown is lifted and socialising indoors increases, making inoculation even more important.
Yesterday Dr Yvonne Doyle, Medical Director of Public Health England, said: "Cases are rising rapidly. We knew that as we opened up cases would increase, but thankfully due to the vaccine, deaths and hospital admissions are not rising as fast as cases.
"If you have not had the vaccine, book your first and second dose as soon as you can.
“Restrictions are currently still in place, it is important to follow them, and when they lift on Monday there are still steps we can all take to protect ourselves and loved ones such as wearing a mask in enclosed spaces, opening a window if you’re meeting in close contact indoors, and getting tested and staying at home if you have symptoms.
"The pandemic is not over, and we must all remain vigilant.”
