According to the Office of National Statistics (ONS), more than 1.7 million people are currently infected in the UK – a rise of 23 per cent on the previous week.
The rise in cases has been driven by two subvariants of the original Omicron strain that sparked the country’s fourth wave last December.
With large swathes of the population having already caught the virus during the course of the pandemic, reinfections are increasingly common - particularly since the arrival of Omicron.
According to the latest UK Health Security Agency (UKHSA) analysis, BA.4 is growing around 19.1 per cent faster than BA.2 while BA.5 is growing 35.1 per cent faster. And each time the virus mutates, the likelihood of reinfection increases.
But just how likely is a reinfection, what are the key symptoms of BA.4 and BA.5 and how much protection do vaccines offer against reinfection over time?
How common are reinfections?
The rate of reinfection increased 15-fold after the arrival of Omicron last December, according to ONS data.
This is partly down to Omicron’s extensive mutations, which allow it to evade the immunity conferred by previous infection. It could explain why so many people who had been vaccinated or previously infected caught the virus again over the Christmas period.
Both BA.4 and BA.5 have now shown evidence of being able to evade the immunity from an original Omicron infection, according to experts.
“The original Omicron BA.1 variant was itself massively immune-evasive, causing a huge breakthrough caseload, even in the vaccinated,” Danny Altmann, a professor of immunology at Imperial College London, told the Guardian.
“It is also poorly immunogenic, which means that catching it offers little extra protection against catching it again. On top of that, there’s now further evidence of the very marginal ability of prior Omicron to prime any immune memory for BA.4 or 5, the sub-variants that seem to be driving the latest wave of infections.”
Early data on reinfections related to the new subvariants appears to back up Prof Altmann’s claim.
Researchers at Harvard Medical School found that both BA.4 and BA.5 appeared to escape antibody responses among those who had previous Covid infection and those who had been vaccinated three times.
Dr. Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center at Harvard, told CNN: “Our data suggest that these new Omicron subvariants will likely be able to lead to surges of infections in populations with high levels of vaccine immunity as well as natural BA.1 and BA.2 immunity.
“However, it is likely that vaccine immunity will still provide substantial protection against severe disease with BA.4 and BA.5.”
Do Omicron and BA.4 and BA.5 have different symptoms?
Omicron itself marked a shift in symptoms from previous variants, including Delta and the original Wuhan strain.
A study by Kings College London and the ZOE Covid App, published last April, found that the most consistent symptoms in Omicron were a sore throat, a hoarse voice and headaches.
Researchers also found that some of the more debilitating symptoms, such as brain fog, eye burning, dizziness and fever were significantly less prevalent in Omicron cases.
There is currently “no evidence” to suggest that BA.4 and BA.5 cause more severe illness than previous variants, according to early research from the UK Health Security Agency (UKHSA).
It is unclear whether BA.4 and BA.5 produce different symptoms, but scientists have not noted any changes yet.
Will my symptoms be milder if I am reinfected?
In general, Covid becomes progressively milder in patients due to the immunity developed by previous infections.
However, scientists have noted that the two new subvariants could be evolving to target lung cells – making them closer to the more severe Alpha and Delta variants.
Dr Stephen Griffin, a virologist at the University of Leeds, said: “It looks as though these things are switching back to the more dangerous form of infection, so going lower down in the lung.”
What difference does vaccination make?
As Omicron is constantly evolving, scientists have warned that the current batch of vaccines being used across the globe may be due an update – even if they continue to offer good protection against severe illness.
Meagan Deming, a virologist and vaccine scientist at the University of Maryland School of Medicine in Baltimore, told Nature that she believes it’s time for new jabs to be rolled out to counter new sub variants.
“The virus is changing, and what worked two years ago may not work for future variants,” she added.
There is no specific date on the efficacy of vaccines against the BA.4 and BA.5 strain. However, protection against BA.2 rose to around 70 per cent four weeks after a third vaccine dose, according to government surveillance data published in March.