WHO Weekly Epidemiological Report On COVID (#55) - Addition Of Mu Variant As VUI

 

COVID-19 cases reported weekly by WHO Region, and global deaths, as of 29 August 2021

#16,156

Last May, with COVID cases declining and vaccine uptake on the rise - and nearly 90% of the world's population living in the northern hemisphere and moving into summer - there were hopes that the COVID pandemic might give us a few months respite. 

But, as the chart above illustrates, summer weather has proved little deterrent to the coronavirus. 

We've now seen impressive waves in the fall/winter, the spring, and most recently, over the summer months, making COVID a legitimate 4-season threat.  Admittedly, the global emergence of a new, and highly transmissible, Delta variant in the spring radically changed the dynamics of the pandemic. 

When you compare the rate of COVID during August of 2021 to August of 2020, you see more than a 2-fold increase.  What that portends for this winter isn't certain, but no one should assume this is COVID's last hurrah. 

In yesterday's WHO COVID epidemiology report, they report that the number of cases and deaths last week were comparable to the week before, albeit with modest declines everywhere but the Western Pacific region. 

Global overview
Data as of 29 August 2021

With just under 4.4 million new cases reported this week (23-29 August), the number of new cases reported globally remains similar to the previous week after having increased for nearly two months (Figure 1). In the past week, all regions reported either a decline (Regions of Africa and the Americas) or a similar trend (Europe, South-East Asia and Eastern Mediterranean Regions) in new cases, except for the Western Pacific Region which reported a 7% increase as compared to previous week.

The number of deaths reported globally this week was also similar to last week, with just over 67 000 new deaths reported. The Eastern Mediterranean and Western Pacific Regions reported an increase in the number of weekly deaths, 9% and 16% respectively, while the South-East Asia Region reported the largest decrease (20%). The numbers of deaths reported in the Regions of Africa, Europe and the Americas were similar to last week. The cumulative number of cases reported globally is now nearly 216 million and the cumulative number of deaths is just under 4.5 million.

The WHO also added a 5th variant to their VOI (Variant of Interest) list - dubbed Mu - which joins Eta, Iota, Kappa, and Lambda on this second tier list.  VOIs - while displaying characteristics worth monitoring - are considered less of an immediate threat than VOCs (Variants of Concern). 

The WHO Synopsis reads:

Based on the latest round of assessments, B.1.621 was classified as a VOI on 30 August 2021 and given  the WHO label “Mu”. This includes the descendent Pango lineage B.1.621.1. This variant is known as 21H in Nextstrain nomenclature. The Mu variant has a constellation of mutations that indicate potential properties of immune escape. Preliminary data presented to the Virus Evolution Working Group show a reduction in neutralization capacity of convalescent and vaccinee sera similar to that seen for the Beta variant, but this needs to be confirmed by further studies.

Since its first identification in Colombia in January 2021, there have been a few sporadic reports of cases of the Mu variant and some larger outbreaks have been reported from other countries in South America and in Europe. As of 29 August, over 4500 sequences (3794 sequences of B.1.621 and 856 sequences of B.1.621.1) have been uploaded to GISAID from 39 countries. 

Although the global prevalence of the Mu variant among sequenced cases has declined and is currently below 0.1%, the prevalence in Colombia (39%) and Ecuador (13%) has consistently increased. The reported prevalence should be interpreted with due consideration of sequencing capacities and timeliness of sharing of sequences, both of which vary between countries. More studies are required to understand the phenotypic and clinical characteristics of this variant. The epidemiology of the Mu variant in South America, particularly with the co-circulation of the Delta variant, will be monitored for changes.

Outside Colombia and Ecuador, B.1.621 has been getting crushed by Delta, and so it remains to be seen whether it can compete with Delta - or other emerging variants - going forward.  

A recent paper in Infection, Genetics and Evolution provides additional background.

Characterization of the emerging B.1.621 variant of interest of SARS-CoV-2

Highlights

• Monitoring the emergence of new variants of SARS-CoV-2 in real time is a worldwide priority.

• Emerging variants of SARS-CoV-2 may have high impact biological implications for public health.

• The SARS-CoV-2 B.1.621 variant of interest was characterized by several substitutions: T95I, Y144T, Y145S, 146N, R346K, E484K and N501Y in spike protein

• Genetic diversification of SARS-CoV-2 and the appearance of variants with potential impact of public health.

While Mu, Lambda, Beta, Gamma, and potentially other variants may throw us some curveballs in the months ahead - particularly if one should manage to evolve substantially away from the vaccine's protection -  for now Delta remains our biggest challenge.