A new Covid strain could re-infect people within weeks of them recovering from the virus, doctors from around the world fear.
Medics have long found those who are infected with Covid then have a level of immunity in the weeks afterwards, making it difficult to become re-infected with the virus for some time.
However BA.5, which has become the new dominant infection in the United States, has cast doubt on the notion, with people reporting testing positive again within a short while of recovering from Covid, The Mirror reports.
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Andrew Roberston, chief health officer in Western Australia, told News.com.au : "What we are seeing is an increasing number of people who have been infected with BA.2 and then becoming infected after four weeks.
"So maybe six to eight weeks they are developing a second infection, and that's almost certainly BA.4 or BA.5."
Immunology professor Danny Altmann, author of a recent paper on the strain wrote in the Guardian how Omicron infections were a “poor booster” of immunities to other Omicron infections.
He added: “Most people – even when triple-vaccinated – had 20 times less neutralising antibody response against Omicron than against the initial ‘Wuhan’ strain.
“Omicron infection was a poor booster of immunity to further Omicron infections”.
“It is a kind of stealth virus that gets in under the radar, even having had Omicron, we’re not well protected from further infections.”
Earlier this week scientists called for the return of a 10-day self-isolation period to protect the NHS from an expected winter surge.
A Lancet study has confirmed for the first time exactly how long we are infectious revealing two thirds of people who catch the virus are still contagious to some extent after five days.
Legally enforced self-isolation periods have now been scrapped and NHS guidance is currently to do so for just five days after testing positive.
That is despite infection rates still running relatively high with around one in every 25 people having it.
Cases are expected to surge as the summer ends, driving people indoors to socialise at a time when all pandemic restrictions such as mask wearing have been scrapped.
The new trial by Imperial College London carried out detailed testing analysis on 57 participants from the point they were exposed to the virus. It is the first to do so outside of a laboratory setting.
The average infectious period was five days and people were less contagious as time passed. However one-quarter of participants were still infectious at day seven.
Scientists also called for a return of the requirement to record two negative lateral flow tests before leaving self isolation between days five and ten.
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