#16,575
The remarkable tsunami of Omicron cases, which began in late November of last year, is showing signs of receding - at least in most parts of the world - although the future impact of Omicron's subvariants (BA.1, BA.2, BA.1.1) remain uncertain.
The notable exception right now is the Western Pacific region, where South Korea today reported more than 90,000 new cases, Hong Kong continues to struggle, and China is fighting fiercely to keep the virus from spinning out of control.
The latest WHO weekly epi report shows double-digit declines in cases in all other regions, although COVID deaths - a trailing indicator - continued to rise (4%) globally over last week.
During the week of 7 to 13 February 2022, the global number of new COVID-19 cases decreased by 19% as compared to the number reported during the previous week, while the number of new deaths remained similar to that of the previous week. Across the six WHO regions, just over 16 million new cases and just under 75 000 new deaths were reported. As of 13 February 2022, over 409 million confirmed cases and over 5.8 million deaths have been reported globally.
At the regional level, the Western Pacific Region reported an increase of 19% in the number of new weekly cases while all other regions reported decreases: the South-East Asia Region (37% decrease), the Region of the Americas (32% decrease), the African Region (30% decrease), the European Region (16% decrease) and the Eastern Mediterranean Region (12% decrease). The number of new weekly deaths increased in the Eastern Mediterranean Region (38%), the Western Pacific Region (27%), the African Region (14%) and the Region of the Americas (5%), while it remained similar to that of the previous week in the European Region and decreased in the South-East Asia Region (9%).
This week's update also includes a Special Focus: Update on SARS-CoV-2 variants of interest and variants of concern.
While yesterday's CDC Nowcast report indicated that the vast majority of COVID cases in the U.S. are now due to Omicron subvariant BA.1.1, the primary focus of this report is BA.2, which is growing in dominance in other parts of the world.
Some excerpts include:
Geographic spread and prevalence of VOCs
The current global epidemiology of SARS-CoV-2 is characterized by the global dominance of the Omicron variant. All other variants, including VOCs (Alpha, Beta, Gamma and Delta) and VOIs (Lambda and Mu) continue to decline in all six WHO regions. Among the 432 470 sequences uploaded to GISAID with specimens collected in the last 30 days 1,425 227 (98.3%) were Omicron, 7 191 (1.7%) were Delta and one (<0.1%) was Lambda. During this same period, there were no Alpha, Beta, Gamma or Mu sequences reported. To note, global VOCs and VOIs distribution should be interpreted with due consideration of surveillance limitations, including differences in sequencing capacities and sampling strategies between countries, as well as delays in reporting.
Special Focus: Update on BA.2 Pango lineage of the Omicron variant of concern
Since the designation of B.1.1.529 as a VOC on 26 November 2021, several lineages have been identified. These include Pango lineages BA.1, BA.1.1, BA.2 and BA.3, which are all being monitored by WHO under the umbrella of ‘Omicron’.
Recent data on BA.2 is summarised based on a targeted literature search and an assessment based on the framework applied by the UK Health Security Agency (UKHSA). 1 The Annex 3 provides further information on how the evidence was gathered and appraised.
Epidemiology
The prevalence of BA.2 among sequenced Omicron cases globally submitted to GISAID has been steadily increasing, 2 reaching 21.09% in week 5 of 2022. 3 As of 14 February, 10 countries reported a predominance of BA.2 (>50%): Bangladesh, Brunei Darussalam, China, Denmark, Guam, India, Montenegro, Nepal, Pakistan, Philippines. However, there are differences between regions observed, with the South-East Asia Region reporting the highest prevalence of BA.2 among Omicron sequences (44.7%) and the Region of the Americas reporting the lowest prevalence (1%).
This analysis is based on all sequences submitted to GISAID with samples collected from 13 January to 11 February 2022.
(SNIP)
Examples of countries which have seen an increase in the prevalence of BA.2 include: South Africa where the prevalence rose from 27% on 4 February 2022 4 to 86% by 11 February 2022 5 ; the United Kingdom 6 where the prevalence increased six-fold from 17 to 31 January 2022 (from 2.2% to 12%); Denmark where the prevalence doubled from week 52 of 2021 to week 2 of 2022 (from 20% to 45%) and became the dominant variant (66% of sequenced by week 3 of 2022 7 ) and the United States of America where the prevalence tripled from 1.2% during the week ending 29 January 2022 to 3.6% during the week ending 5 February 2022. 8 The prevalence of BA.2 appears to be increasing both in countries experiencing a decline in Omicron cases and in countries that are in the growing phase of the wave.
Transmission
Early evidence from limited studies suggests BA.2 is more transmissible as compared to BA.1. Estimates of growth rates in Denmark indicate that BA.2 is 30% more transmissible than BA.1. 7 An analysis of GISAID data 9 shows a growth rate advantage of BA.2 over BA.1 in all 43 countries with sufficient sequence data and co-circulation of the two lineages, translating to a pooled mean transmission advantage (i.e. relative difference in effective reproduction numbers) of 84% (95% CI: 68% – 101%) across epidemiological contexts under the assumption of an unchanged generation time.
(SNIP)
Disease severity
At present, there is limited evidence on the severity of BA.2 relative to BA.1 or other Omicron Pango lineages. As the proportion of BA.2 has steadily increased in recent weeks in the United Kingdom, there has been a consistent decrease in the number of hospitalizations and deaths. 15 In the United States of America, 8 there have been decreases in hospitalizations and increases in the number of deaths across successive weeks. In this context, a 5.9% reduction in the number of new deaths was reported during the week ending 8 February 2022 as compared to the previous week ending 1 February 2022. However, this does not allow inferences to be made as to the relative severity of BA.2 as in both these countries, BA.1 or BA.1.1 was the dominant Pango lineage during this period.
An analysis conducted in Denmark showed no difference in risk of hospitalisation between those infected with BA.2 and those infected with BA.1, although as BA.2 has become the dominant variant, there has been a recent rise in the number of hospitalisations and deaths in the country. 16 In Nepal, as published on 1 February 2022, ten of eleven samples sequenced at Kathmandu University, Nepal were of the BA.2 lineage. 17 However, the number of patients in hospital in the Kathmandu Valley has been decreasing since a peak on 23 January 2022 with the numbers in intensive care and on mechanical ventilation also showing some initial signs of a decrease. In South Africa, BA.2 now accounts for 86% of all sequences; however, hospital admissions continue to decline. 1
Overall, there is no difference in severity when looking at countries where BA.2 is dominant and those where BA.1 is dominant.
(SNIP)
While we've seen relatively little data on the BA.1.1 subvariant, we have seen some evidence suggesting that (BA.1.1, BA.2 and BA.3) are all more transmissible than BA.1 and Delta. BA.3 remains rare, making the $64 question - in a head-to-head match - which subvariant (BA.2 or BA.1.1) prevails?
In truth, it may make little immediate impact, as we've not seen any big differences in severity between them.
Considering that 90 days ago Delta was still in charge, and we've only been talking seriously about BA.2 for a little over a month, and 30 days ago BA.1.1 wasn't even mentioned in the WHO weekly update, COVID's evolution is progressing with surprising speed.
Meaning I wouldn't want to even hazard a guess what we'll be talking about 3 months from now.
