Waning immunity, easing of restrictions and more transmissible variants are all to blame, experts say
With Covid infection levels at a record high in parts of the UK, the virus is rife once more, with experts noting that one factor is the rise of a variant of Omicron known as BA.2. But what does this mean for reinfections?
Can you get Covid more than once?
Yes. According to the latest weekly Influenza and Covid-19 surveillance report from the UK Health Security Agency (UKHSA), since the beginning of the pandemic to 20 March this year 804,463 possible reinfection episodes have been identified in England – defined as two positive tests more than 90 days apart – with 50,866 of those identified in figures for the most recent week. The agency adds that, so far, 8,717 third episodes and 74 fourth episodes have been identified since the start of the pandemic.
However, as not everyone with Covid takes a test, the figures are likely to be an undercount.
The UKHSA data also shows that while reinfections did occur at low levels earlier in the pandemic, the rate of reinfection shot up towards the end of 2021, before falling and, more recently, rising once more.
Why have reinfections become more common?
While a Covid infection will offer some protection against catching the virus again, this protection wanes over time. Data also suggests reinfection is higher in unvaccinated people, while the severity of the previous infection, and the level of immune response, may also play a role in the risk of reinfection.
In addition, the more people who have had Covid, the greater the pool of individuals that could potentially be reinfected, and with infection levels high – and restrictions now eased – the chance of a susceptible person being exposed to Covid is raised.
What’s more, the body’s immunity – whether from past infection or vaccination – may hold up better against some variants than others.
These factors became particularly evident when Omicron reached the UK towards the end of 2021, with the variant being both highly transmissible and able to dodge the body’s immune responses to other variants or vaccination to a significant degree.
“Reinfections are currently rapid and frequent, far more than previous waves,” said Prof Danny Altmann, an immunologist at Imperial College London. “Partly [because of] the simple trilogy of transmissible variant, immune waning, [and] fewer precautions.”
How likely are you to get BA.2 if you have had the original Omicron variant?
BA.2 is a variant of Omicron, with UKHSA data suggesting it is even more transmissible than the original, BA.1 – although the risk of hospitalisation appears to be no greater. BA.2 is currently the most common Covid variant across the UK.
Altmann said BA.2 does not seem to show differences compared with BA.1 in its ability to evade the body’s immune responses. The point is highlighted by research from the US, with the authors noting the rise of BA.2 following the surge of BA.1 “is probably related to increased transmissibility rather than to enhanced immunologic escape”.
While UKHSA data, as well as preliminary research from Denmark, suggests infection with BA.2 shortly after an infection with BA.1 is possible, it seems it is – at least for now – very rare, with the Danish research finding such reinfections were mostly in young, unvaccinated individuals.
But both BA.1 and BA.2 are relatively new – and it takes time for reinfections to occur.
“We are at the start of the 90-day period for possible reinfection with BA.2 following a BA.1 infection and there is a need for ongoing surveillance but there are no early indications of a specific reinfection issue with this scenario,” notes the latest UKHSA technical briefing on Covid variants.
However Altmann, drawing on his own research, sounded a note of caution.
“The surprising aspect is that even, say, compared to expectations from common colds, Omicron seems so poorly immunogenic that it doesn’t even stimulate good immunity to itself – something that should be noted by all those thinking they may as well go out and get infected as a ‘natural booster’,” he said.
Source:theguardian.com