The findings from a University College London (UCL) study was based on 8,517 people in England and Wales and found 96.42 per cent of people, who had either vaccine, had developed antibodies 28 to 34 days after their first dose.
That rose to 99.08 per cent within seven to 14 days of the second jab.
Dr Maddie Shrotri, the lead author of the paper, said: “This is one of the earliest real-world vaccine studies in the UK and it is fantastic news.
“How well these vaccines work is remarkable, especially given the speed at which they’ve been developed. It’s a real feat of science in the face of the most devastating pandemic in a century.”
None of the participants of the study had antibodies prior to the first dose of the vaccine. Anyone with antibodies was omitted.
The study found antibody rates initially increase quicker among those who have had the Pfizer/BioNTech vaccine than those with the Oxford/AstraZeneca.
However, after one month the recipients showed almost identical antibody positivity rates.
The UCL Virus Watch project team also found one dose of the vaccines stimulated the production of fewer antibodies in older people, but that changed after the second dose with all ages achieving high antibody levels.
Antibody levels after one jab are also weaker in people with some underlying health conditions, including heart disease, cancer and diabetes, and also those taking immune system suppressing medication.
This disappeared once all participants had their second vaccine, the researchers said.
“The UCL Virus Watch data shows that for older adults and for people with underlying health conditions, the antibody response is a bit weaker after the first dose of the vaccine, but strong after the second dose,” said Prof Rob Aldridge, the chief investigator of the UCL Virus Watch study.
“It is a timely reminder about the importance of getting the second dose of the vaccine. But it is also reassuring – vaccines are our way out of the pandemic.”
The co-authors of the paper said their findings show that everyone should have both doses of their vaccine so they can be considered “safe”, notably older adults and people with existing illnesses.