It comes as new data suggests people who have received the Pfizer jab have fewer antibodies targeting the Delta variant compared to other strains. The research, from the Francis Crick Institute and the National Institute for Health Research (NIHR) UCLH Biomedical Research Centre, supports reducing the gap between first and second doses.
The data found that after just one dose of the Pfizer jab, recipients were less likely to develop antibody levels against the Delta variant, also known as the Indian strain, compared to those seen against the UK variant, now known as Alpha.
But researchers said antibody levels alone do not predict vaccine effectiveness and further studies are needed.
Speaking on BBC Newsnight on Friday, Professor Rosalind Eggo, from London School of Hygiene and Tropical Medicine, explained why a second dose is “really important”.
She said: “There’s some very early evidence that our current vaccines don’t work quite as well against the Delta variant as against the previous variants so there’s a little bit of loss in that vaccine effectiveness.
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“Yes we’re in a different situation than last year with the Alpha variant which also was more transmissible and also was maybe a little bit more severe.
“But what we learned from that was how quickly things can change with Covid and that it’s much easier and wiser to make decisions when there’s few cases than when there’s many.”
On Friday, official figures showed that the UK recorded 6,238 daily COVID-19 cases and 11 further deaths in the latest 24-hour period.
Official data also revealed on Friday that the Covid R number in the UK is estimated to be between 1.0 and 1.2 – rising from the previous 1.0 and 1.1 figure.
Public Health England data up to June 2 also shows that a total of 12,431 cases of the Delta variant have been confirmed in the UK – a 79 percent increase from the previous week.