SARS-CoV-2 Variant Update
All viruses, including SARS-CoV-2, the virus that causes COVID19, change over time. Most changes have little to no impact on the virus’ properties. However, some changes may affect the virus’s properties, such as how easily it spreads, the associated disease severity, or the performance of vaccines, therapeutic medicines, diagnostic tools, or other public health and social measures. During late 2020, the emergence of variants that posed an increased risk to global public health led to the characterization of specific Variants of Interest (VOI) and Variants of Concern (VOC) to better monitor the COVID19 pandemic.
A SARS-CoV-2 variant is considered to be a VOI if it meets the following criteria:
- Has genetic changes that are predicted or known to affect virus characteristics such as transmissibility, disease severity, immune escape, diagnostic or therapeutic escape; AND
- Identified to cause significant community transmission or multiple COVID19 clusters, in multiple countries with increasing relative prevalence alongside increasing number of cases over time,
A VOC is a SARS-CoV-2 variant that meets the definition of a VOI and has been demonstrated to be associated with one or more of the following changes at a degree of global public health significance:
- Increase in transmissibility or detrimental change in COVID19 epidemiology, OR
- Increase in virulence or change in clinical disease presentation, OR
- Decrease in effectiveness of public health and social measures or available diagnostics, vaccines, therapeutics.
As of August 31, WHO reported that cases of the Alpha variant had been reported in 193 countries, while 141 countries had reported cases of the Beta variant; 91 countries had reported cases of the Gamma variant; and 170 countries had reported cases of the Delta variant.
On August 30, 2021, the WHO designated SARS-CoV-2 variant B1.621 strain a variant of interest and assigned the Greek alphabet name Mu. It is the fifth VOI being monitored by the WHO. Mu was first detected in Colombia in January 2021 and has been identified in 39 countries including the United States, South Korea, Hong Kong, Japan, Ecuador, Canada, and parts of Europe. Approximately 2,000 cases have been detected in the US so far. Most cases have been recorded in California, Florida, Texas, and New York.
The Mu variant has a constellation of mutations that indicate potential properties of immune escape. Preliminary data presented to the Virus Evolution Working Group has shown a reduction in neutralization capacity of convalescent and vaccinee sera like that seen for the Beta variant, but this finding needs to be confirmed.
Paul Cárdenas, professor of infectious diseases and genomics at Universidad San Francisco de Quito in Ecuador said Mu is more transmissible than the original coronavirus strain. It has been able to outcompete gamma and alpha in most parts of Ecuador and Colombia. Mu accounts for at least 39%of cases in Colombia and 11% in Ecuador. Prevalence is steadily rising in those countries.
WHO has warned that reports on the variant’s prevalence should be interpreted cautiously because of variations in countries’ viral gene sequencing capabilities and timeliness of sequence sharing. WHO is continuing to monitor Mu’s epidemiological evolution. Mu has yet to be designated a variant of interest or concern by the Centers for Disease Control and Prevention. During a press briefing on September 3, Anthony Fauci said Mu was not an “immediate threat right now” and was “not even close to being dominant.”
A preprint article posted on medRxiv on August 24, 2021, by South African researchers described another potential VOI that was first identified in May 2021 and likely originated from the C.1 viral lineage that dominated the first wave of SARS-CoV-2 infections in South Africa. The C.1.2 variant is believed to have between 44 and 59 mutations in regions of the spike protein, receptor binding domain (RBD), and furin cleavage site. This VOI contains more mutations than previous VOI and VOC. The mutations have been associated with increased neutralizing antibody evasion, increased transmissibility, and potentially increased viral reproduction.
By August 13, 2021, the variant had been detected in most South African provinces, as well as in the Democratic Republic of the Congo, Mauritius, New Zealand, Portugal, and Switzerland. Despite the wide geographic spread, prevalence of C.1.2 in tested samples has remained low. However, monthly increases in prevalence have been similar to those seen in the early stages of the Beta and Delta variants. The research team is currently assessing the effectiveness of vaccines against this variant. WHO has not yet designated this variant to be a VOI or VOC.
References
Weekly epidemiological update on COVID-19 - 31 August 2021, Edition 55, Emergency Situational Updates,
https://www.who.int/publications/m/item/weekly-epidemiological-update-on-covid-19---31-august-2021
Scheepers C et al. The continuous evolution of SARS-CoV-2 in South Africa: a new lineage with rapid accumulation of mutations of concern and global detection, medRxiv, August 24, 2012, https://doi.org/10.1101/2021.08.20.21262342
