Dr. Armelle Pérez-Cortés Villalobos
The emergence of new SARS-CoV-2 variants is an expected phenomenon, given that virus transmission has not stopped. Most of the changes the virus undergoes over time have little or no effect on its properties. However, some changes may have implications for aspects that could be relevant to the management and spread of COVID-19 cases.
For this reason, the World Health Organization (WHO) proposed classifying SARS-CoV-2 variants as variants of interest. These variants exhibit changes in their genome and, as demonstrated or predicted, may affect the virus's characteristics, such as its transmissibility, the severity of the disease it causes, its ability to evade the immune system, its detectability by diagnostic methods, or its susceptibility to drugs. In recent weeks, we have heard information about two variants of interest, about which we continue to learn: lambda and mu.
Lambda variant
The lambda variant, also known as lineage C.37, is a variant of SARS-CoV-2 that was initially detected in Peru in August 2020 and designated as a variant of concern in June 2021. To date, it has been detected in 44 countries worldwide, and by April 2021, it accounted for more than 80% of COVID-19 cases in Peru. It has since spread rapidly to other Latin American countries, such as Argentina, Chile, and Ecuador. In Mexico, this variant was identified in April 2021, and as of August 9 of this year, 189 cases had been detected in the country.
Lambda exhibits multiple mutations that suggest potential phenotypic implications, such as potentially increasing its transmissibility or conferring resistance to neutralizing antibodies. These mutations are located in the spike protein, including G75V, T76I, del247/253, L452Q, F490S, D614G, and T859N. Currently, there is very limited evidence regarding the full impact of these genomic changes, as well as a lack of robust studies to understand their clinical impact, including studies that would allow us to validate the effectiveness of SARS-CoV-2 vaccines against this variant.
mu variant
The mu variant, also known as lineage B.1.621, was recently classified as a variant of interest on August 30, 2021. This variant was initially identified in Colombia in January 2021, and subsequently, sporadic cases and some large outbreaks of COVID-19 caused by the mu variant have been reported in other countries in South America and Europe. As of August 29, 4,500 sequences had been received in GISAID from 39 countries, and the prevalence of the mu variant in sequenced cases has clearly decreased; however, the prevalence in Colombia and Ecuador continues to increase considerably.
This variant has a constellation of mutations that indicate it could potentially possess immune escape properties. Preliminary studies have shown a reduction in the neutralizing capacity of vaccines and convalescent plasma similar to the beta variant; however, this finding needs to be confirmed in clinical trials.
The emergence of new SARS-CoV-2 variants is an expected phenomenon, and the recent addition of lambda and mu to the classification of variants of concern only underscores the need to monitor and continue understanding and studying the clinical and epidemiological implications of both variants. To date, there is no scientific evidence to suggest that the available COVID-19 vaccines are ineffective against these two variants. It is important to remember that vaccines have consistently demonstrated high effectiveness against severe illness and death from COVID-19, including cases caused by variants of concern and interest.