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The BA.5 Omicron sub-variant, which is known to evade immunity induced both by vaccines as well as prior infection, has the potential to reinfect you with Covid again "within weeks", global researchers have said.

BA.5, together with BA.4 and other sub-variants, are said to be behind the current surge in infections seen in a slew of countries including India, China, US, and European nations, notably the UK and Italy.

It has been a common assumption during the pandemic that being infected with a Covid variant provides a natural immune boost, enabling one's immune system to better recognise and fend off infection in the future.

However, Omicron BA.5 proves to be different, with several researchers terming it as "the most easily transmissible Covid variant to date".

"The main reason this variant has become the predominant one that is now circulating is that it is able to evade previous immunity," said Dean Blumberg, chief of Paediatric Infectious Diseases at University of California, Davis, Children's Hospital. "Even people who have partial immunity from a previous infection or vaccination can still have a breakthrough infection."

That means even if you were infected in 2020 with Delta or even Omicron BA.1 last winter, you can still get BA.5. Your previous immunity does not protect you from the latest strain.

"What we are seeing is an increasing number of people who have been infected with BA.2 and then becoming infected after four weeks," Andrew Roberston, the chief health officer in Western Australia, was quoted as saying to News.com.au.

"So maybe six to eight weeks they are developing a second infection, and that's almost certainly BA.4 or BA.5," he added.

This may be explained by a recent study, published in the journal Science, which showed that Omicron provides a poor natural boost of Covid immunity against reinfection even with Omicron and also in people who are triple-vaccinated.

Researchers at the Imperial College London called the BA.5 "an especially stealthy immune evader".

"Not only can it break through vaccine defences, it looks to leave very few of the hallmarks we'd expect on the immune system - it's more stealthy than previous variants and flies under the radar, so the immune system is unable to remember it," said Professor Danny Altmann, from Department of Immunology and Inflammation at Imperial.