Delta raises COVID reinfection risk by 46%: Study

People who have previously had COVID-19 are more likely to be reinfected with the Delta strain than with previous variants, research carried out in the UK suggests.
 
The findings were published last month in the most recent technical briefing about SARS-CoV-2 variants of concern released by Public Health England (PHE).
 
In an analysis of cases recorded from 12 April to 27 June this year, there were a total 83,197 people who tested positive for COVID-19 in the 11-week period covered by the study. Of those, 980 were possible reinfections.
 
According to the briefing, the data suggests the risk of reinfection does not increase until 180 days after the first infection.
 
The authors write that ‘preliminary analysis of national surveillance data finds an increased risk of reinfection with Delta, compared to Alpha’, with the overall chances around 46% higher compared to the Alpha variant.
 
The analysis of positive cases within the general population appears to be reinforced by a study monitoring positive cases across 35,684 National Health Service workers in England, with a rising number of reinfections in the most recent months as Delta increasingly dominated in the area.
 
The authors also suggest that the emergence of a new strain will likely further increase the chances of reinfection.
 
‘The incidence of new infections and potential reinfections … is monitored and would be expected to rise if a new variant became highly prevalent and was able to escape predominantly vaccine-derived immunity,’ the document states.
 
The authors say further work analysing the risk of reinfection is being carried out. The briefing does not include any further details on the severity of the symptoms of those with potential reinfections.
 
Previous studies have explored highly variable immune responses triggered after infection, with some people thought to lose their protection just months after first developing symptoms.

Dr Lara Roeske, a member of the RACGP’s COVID Working Group, told newsGP the indications are unsurprising.
 
‘This is not an unexpected path for a virus to take,’ she said.  ‘Viruses are particularly dynamic in their ability to change to put themselves at an advantage so they can continue to transmit and spread.
 
‘This idea of change I don’t think is new to GPs – we can understand it from a biological, scientific principles point of view.’
 
Dr Roeske suggests there is a level of reassurance given the low number of possible reinfection cases, which was calculated at 1.2% of the total number of cases analysed for the PHE study.
 
‘While the propensity [for reinfection] was greater, the overall number was a very low percentage, which provides a level of comfort,’ she said.
 
‘What the paper does tell us, is that even with those concerns about Delta’s infectivity … and its propensity for reinfection, if you are fully vaccinated you are still less likely to be hospitalised than those who haven’t been.
 
‘Our incredibly important role is advocating for our patients and advocating for vaccination.’
 
The first reinfection case of COVID-19 was confirmed last August, when a man in Hong Kong was found to have had two different strains of the virus.
 
Associate Professor Ian Mackay, a virologist from the University of Queensland, told newsGP at the time that it was not a surprise and that he believed the true number was likely to be much higher than officially recorded.
 
‘I suspect reinfection is happening a lot more often than we have bothered to find yet. It’ll be happening more frequently in areas where there’s lots of transmission,’ he said.
 
Despite transmission in Australia remaining much lower than most other countries for now, Dr Roeske says the study – and the virulence of the Delta strain – reinforces the need for essential protocols.
 
‘There’s some basic principles we as GPs continue to adhere to,’ she said. ‘Our protection control processes, appropriate protection, PPE and the use of judicious triaging of patients – and then of course management and isolation as required. All the principles apply.’
 
While reinfections are not a surprise, she says a key role for GPs is in managing people’s understanding and the potential for misinterpretation.
 
‘What can be unexpected or difficult to control is the way it’s messaged within the media and we have a really important role to play around dispelling those falsehoods, encouraging vaccination, and reassuring our patients and our communities to keep on top of it,’ Dr Roeske said.
 
‘The part where we come in is in the community. For them, it is novel that a virus can do this – for us as GPs, it’s about providing an explanation, mitigating the fear, dealing with the falsehoods.
 
‘That’s part of the war against the virus that GPs are really well equipped to wage, and to wage successfully.’
 
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