Close to 90 countries across the world have reported the presence of the Omicron variant of Sars-CoV-2 on their shores as of this weekend. Last week, the World Health Organization (WHO) said that preliminary evidence appears to indicate that vaccines may be less effective against infection and transmission linked to Omicron, which also carries a “higher risk of re-infection”. There have been reports that the Omicron variant takes over from Delta as the main circulating virus within weeks of the
Close to 90 countries across the world have reported the presence of the Omicron variant of Sars-CoV-2 on their shores as of this weekend. Last week, the World Health Organization (WHO) said that preliminary evidence appears to indicate that vaccines may be less effective against infection and transmission linked to Omicron, which also carries a “higher risk of re-infection”. There have been reports that the Omicron variant takes over from Delta as the main circulating virus within weeks of the first cases being reported.
With these abilities, the new variant has sparked concerns that it could elongate the fight against the pandemic by several months. Here is a look at two case studies from regions in Europe – London and Denmark – that were one of the first regions in the continent to report large-scale Omicron outbreaks.
Both these regions have been selected because their local governments have perhaps one of the most rigorous testing, screening, and data-sharing programmes that exist anywhere in the world. This means that they have been publishing data from genome sequencing with a lag of only a few days, enabling scientists across the world to analyse almost in real-time the spread of the virus.
Very few countries (or even localised regions) consistently release data on the spread of a particular variant. This exercise is generally done by extrapolating genome sequencing data on the overall case turnout. This system is utilised by agencies such as the US’s Centers for Disease Control and Prevention (CDC) to determine the prevalence of a variant.
However, one advantage that Omicron’s heavily mutated nature offers is that in a widely used RT-PCR test, one of the three target genes is not detected (called S-gene dropout) and this can therefore be used as a marker for this variant, while sequencing is awaited. Using this approach, some regions have been tracking this variant in near real-time, offering early clues on how prevalent it is.
So, what do the numbers from London and Denmark show?
In absolute numbers, there were 4,639 new cases of the Omicron variant reported every single day in London for the week ending December 17 (the latest this data has been released). Exactly a week before that, this number was 850 new infections a day on average. This means that daily Omicron cases have increased 5.5 times in just one week.
In Denmark, reported Omicron infections are increasing at an even higher rate. For the week ended December 15 (also the latest date for which this data was made available), there were 2,397 new infections of the variant every single day on average. A week before that, this number was 290. So, in Denmark, cases have increased more than 8-fold in just a week.
In both cases, the seven-day average of new Omicron cases has quadrupled in just five days.
A closer look at the region’s Omicron cases and the proportion of other variants in circulation paint an even more grim picture.
In London, Omicron cases have been outstripping all other variants for the last seven days of data that has been published. On December 17, there were seven times as many cases of Omicron in the city than there were of all other variants combined (457 cases of other variants against 3,180 Omicron infections reported on the day) – or 87% of all cases detected in London were Omicron, according to data released by UK Health Security Agency (UKHSA). Just two weeks ago, Omicron was responsible for just 3% of all infections in the city; and two weeks before that, it was 0.3% of all Covid-19 cases.
A similar story is playing out in Denmark. In the last two weeks of data being released, the share of Omicron in overall cases has gone from 1.6% to 30.6% (for the week ended December 15), according to data released by the Statens Serum Institut (SSI). Furthermore, SSI dataEDIT also shows that almost 75% of the patients that had been infected by the Omicron variant had received both doses of the Covid-19 vaccine.
On Monday, CDC announced that the Omicron variant is now the most dominant strain in the country, accounting for over 73% of new coronavirus cases less than three weeks after the first was reported. Just a week before that, only 3% of new cases in the US were Omicron, according to CDC.
While scientists are rushing to figure out why it is so, there appears to be unanimity that the new variant is significantly more transmissible and resistant to immunity. On transmissibility, a recent report by researchers from Imperial College London found that Omicron currently has a reproduction number (denoted as R) of 3, while Delta had 1. A reproduction number represents the number of infections that are caused by one base patient that carries the virus. So, in this case, a single Omicron case leads to three more, and each of those three then pass it on to three more each – leading to 27 cases in just two rounds of onward transmission. At the same time, the Delta variant would have caused only three cases.
These case studies offer a tiny glimpse of a scenario of possible pandemic progression that does appear to be unfolding in nearly every region where Omicron is taking hold – a clear warning for countries (such as India) that are just at the initial stages of what may be Omicron waves.
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