Abstract
The BA.4 and BA.5 subvariants of omicron are driving an increase in covid-19 cases in many countries, reports Clare Wilson
ONE in 25 people in England, or nearly 4 per cent of the country's population, were infected by the coronavirus in the week ending 29 June, according to the latest figures from the UK's Office for National Statistics (ONS). The equivalent figures for the rest of the UK were 1 in 17 people in Scotland, 1 in 20 people in Wales and 1 in 19 people in Northern Ireland, with a total of around 2.7 million infections across the UK that week. The proportion of infections has roughly doubled across the UK since the start of June.
The infections are mainly caused by a growing wave of the BA.4 and BA.5 subvariants of omicron, which were first detected in South Africa in January. These subvariants have now spread around the world and are triggering surges of cases in Australia and many European countries, such as Portugal, Germany and France. They have also become the most common subvariants in the US. This follows previous waves from the BA.1 and BA.2 subvariants of omicron in almost all countries earlier this year, making this the third omicron surge within six months.
Although similar genetically, BA.4 and BA.5 are more transmissible than BA.1 and BA.2, which were more easily passed on than the previous coronavirus variants, such as delta and alpha.
BA.1 and BA.2 have been causing milder illness than previous forms of covid-19, both because of intrinsic features of the viruses and the fact that many people had partial immunity to covid-19 from vaccines and past infections.
Some research in hamsters has suggested that BA.4 and BA.5 are deadlier than BA.2. But a recent study from South Africa suggests the two latest omicron subvariants are similar in illness severity to the first ones, based on the number of people admitted to hospital during the waves. “We are seeing no increase in disease severity,” says Mary-Ann Davies at the University of Cape Town in South Africa.
The fact that BA.4 and BA.5 are more transmissible is causing issues for health services
But it is difficult to compare across countries because of differences in populations, vaccination rates and which coronavirus variants have dominated, she says. For instance, South Africa has a relatively young population and older people tend to experience more severe covid-19. “We are looking at an interplay between the virus and the range of immune responses that the population have,” says Davies.
Other open questions include whether catching BA.4 or BA.5 following a previous covid-19 infection could lead to worse health than just having it once, and the prospects of developing long covid from the new subvariants. A recent study suggested that the risk of long covid from BA.1 and BA.2 is half that of delta, but there hasn't yet been time to learn how BA.4 and BA.5 compare.
Even if the latest omicron surge is similar in illness severity to the first, the fact that BA.4 and BA.5 are more transmissible is still causing issues for health services. In the UK, rising infections are seeing more people admitted to hospital with covid-19, adding to existing issues.
By the end of June, the number of people in UK hospitals with covid-19 had climbed back to levels last seen in April this year. According to the ONS, as of 5 July, 64 per cent of people in English hospitals had an “incidental” covid-19 infection – in other words, it was detected by a screening test and wasn't their primary reason for being in hospital. But such infections can still worsen people's illness and cause difficulties for hospitals, says Tom Lawton, an intensive care doctor in Bradford, UK. “It's extra pressure on a system that really doesn't need it right now.”