Public Health England has upgraded its risk assessment of the Delta variant after national testing data revealed it is more likely to cause reinfections than the Alpha variant, which was first identified in Kent.
The health agency’s analysis found the risk of reinfection with Delta may be 46% greater than with the Alpha variant, with the highest risk seen six months after a first infection – when second cases caused by Delta were 2.37 times more common than with Alpha.
The finding is bolstered by new data from Public Health England’s (PHE) Siren study, which monitors more than 40,000 NHS staff for Covid infections. The latest figures show that positive tests rose steadily from May to July when 1.1% had the virus. Nearly a third of the healthcare workers had Covid before enrolling on the study and more than 95% have been vaccinated.
It is unclear why Delta may be causing more reinfections, but one possibility is that immunity from infections early on in the pandemic may be waning a little and so reducing the body’s defences against the variant which became dominant in the UK this year. PHE said that further work is now being undertaken to examine the risk of reinfection.
In light of the findings, PHE upgraded its risk assessment on “immunity after natural infection” from amber to red for the Delta variant. Reinfections remain a rarity though, accounting for only 1.2% of the 83,197 cases analysed.
The move came as new figures showed how many people in hospital with the Delta variant have had one or both doses of a Covid vaccine. Between 21 June and 19 July, 1,788 people were admitted to hospital after testing positive for Delta. Of these, 54% were unvaccinated while 30% had received both shots. In total, 3,692 people have so far been admitted to hospital with the Delta variant, of whom 2,152 (58%) were unvaccinated and 843 (23%) were fully vaccinated.
Dr Jenny Harries, chief executive of the UK Health Security Agency, said: “This most recent hospitalisation data shows once again just how crucial vaccination is in protecting us from severe illness and death.
“Two doses of vaccine are far more effective against Covid-19 than a single dose, so please make sure that you come forward to get your second dose as soon as you are invited.
“As we emerge from restrictions and vaccine coverage continues to rise, it is important to remember that, while the protection provided by vaccination is excellent, it is not total.”