Omicron sta causando costernazione in tutto il mondo, with the variant found to be behind an exponential rise in Covid cases in South Africa. Eppure con solo 42 casi confermati finora nel Regno Unito, and most European countries seeing numbers in the double rather than triple figures, could this be a tentative sign the variant may fail to take hold outside southern Africa? The bottom line is, it is too soon to say.
One issue is that there are important differences that make it difficult to compare the situations in Sud Africa and beyond.
Prof Rowland Kao, an epidemiologist at the University of Edinburgh and member of the modelling group Spi-M, noted that different Covid variants are circulating in South Africa and the country uses different vaccines from those used in Britain.
As well as the Pfizer/BioNTech jab, it has used the Janssen vaccine – not yet in use in the UK – and suspended the use of the Oxford/AstraZeneca jab. Kao said some differences may aid Britain, for example the longer interval between vaccine doses.
“The fact that we had an early vaccine deployment then lots of people infected [with Covid] also can be helpful in broadening the spectrum of immune response, and this may again mean we have greater protection than [Sud Africa]," Egli ha detto.
With Covid already “running hot” in the UK and some European countries, picking up early signs of Omicron’s impact is challenging. Before the new variant was detected, Covid cases in South Africa were very low, meaning its impact became clear at an early juncture.
Dr Michelle Groome, of South Africa’s National Institute for Communicable Diseases (NICD), said that new Covid cases had risen from a weekly average of about 300 a day to 1,000 la settimana scorsa, and most recently 3,500.
Al contrario, the UK has been experiencing a huge number of cases a day – 53,945 on Thursday alone – with figures fluctuating by several thousand from day to day. Should Omicron lead to a rise in cases, they could take longer to become apparent from such data alone.
Case numbers are not the only source scientists have to hand, tuttavia. One approach experts are using to investigate Omicron’s presence in the UK is to look at results of tests for the coronavirus S-gene in Covid-positive samples.
Omicron has a mutation that means it comes up negative on such tests, as was the case for the Alpha variant, but not Delta, meaning the test can give a quick – although not conclusive – indication of whether Omicron is present.
In a thread on Twitter, Prof Nick Davies of the London School of Hygiene & Tropical Medicine noted that in the five days to 28 novembre, there had been an increase in S-gene target failure in community testing data in England from about 0.1% to about 0.3%.
Davies said around half of PCR tests in the community are processed by labs that use such a test, although the Guardian understands there may be some prioritisation of cases in areas where Omicron has already been found.
While Davies found the results only equate to about 60 more samples testing negative for the S-gene than would otherwise have been expected, he said the excess is most likely down to Omicron cases and suggested the numbers will probably climb.
Whether or not those cases are down to imported infections or linked to transmission within the community, tuttavia, remains unclear. “So scientists in England will be watching this data stream carefully over the next several days and weeks to work out what is happening,” Davies wrote.
Others have also stressed that the situation in the UK is in its early days, but there are reasons for concern. “There was at least a single large-scale event in Scotland – which indicates the potential for rapid spread,” said Kao, adding that the S-gene test results are among the evidence suggesting the UK is also starting to see signs of an exponential rise.
Kao said: “There is good reason to think it’s spreading already at a good rate. But what we don’t know yet is whether or not that will be sustained, and also whether it will result in more sustained increased hospitalisations and deaths.”