The XFG subvariant of COVID-19, nicknamed “Frankenstein,” is a recombinant strain that merges genetic material from two Omicron lineages. Its primary characteristic is its high transmission capacity.
MEXICO CITY (apro).— A subvariant of the SARS-CoV-2 virus, known as “Frankenstein” due to its recombinant nature, has drawn the attention of global health authorities because of its swift spread. Scientifically identified as XFG, this variant is a hybrid of two Omicron lineages and has become the predominant strain in various regions, prompting the World Health Organization (WHO) to classify it as a “variant under monitoring”. Although it is highly transmissible, current reports do not suggest that it causes more severe illness than other circulating variants. The symptoms are similar to those of Omicron, though some clinical reports have pointed out hoarseness as a potential distinctive feature.
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What is a Recombinant Virus Variant?
A recombinant variant of SARS-CoV-2, like XFG, occurs when an individual is infected with two different lineages of the virus at the same time. During the virus replication process within the host cells, the genetic materials from both variants can mix, resulting in the creation of a new virus version that combines features from its “parents”. This natural evolutionary phenomenon has been previously observed with other variants during the pandemic.
The term “Frankenstein”, though not an official scientific designation, has been popularly used to describe these recombinant variants. The nickname references the idea of constructing a new virus from parts of existing ones. At the end of 2022, the term was applied to the subvariant XBB.1.5, a recombination of two Omicron lineages. More recently, in mid-2025, the same nickname has gained prominence again to describe the XFG variant, which is also a fusion of two Omicron subvariants.
What are the Associated Symptoms?
The symptoms observed in individuals infected with the XFG subvariant largely mirror those seen in other Omicron variants. However, one distinctive trait identified is its impact on the voice. Clinical reports have suggested that hoarseness or even temporary loss of voice (aphonia) could be an early sign of infection.
In addition to this peculiarity, the general symptoms include fever, dry cough, sore throat, fatigue, and muscle pain. Nasal congestion and, in some cases, digestive discomfort have also been reported. The loss of taste and smell, a prominent feature in earlier variants like Delta, is less common in Omicron lineages. Organizations such as the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) indicate that, in general, the symptoms of Omicron subvariants, including XBB.1.5, are similar to those of a common cold.
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Why has it Received so Much Attention?
The XFG subvariant, dubbed “Frankenstein,” has captured the attention of health authorities and media due to its rapid global spread. In July 2025, the Oswaldo Cruz Institute in Rio de Janeiro, Brazil, reported that this variant accounted for 62% of COVID-19 cases analyzed in the first week of the month, highlighting its high transmission capacity. The World Health Organization has categorized XFG as a “variant under monitoring” (VUM), meaning that while its spread is closely monitored, there is no evidence to date that it causes more severe illness than other variants.
Previously, the subvariant XBB.1.5, which also received the “Frankenstein” nickname, was described by the WHO in January 2023 as the “most transmissible” detected up to that point. Its advantage was due to mutations that allowed it to bind more effectively to human cells and evade immunity generated from previous infections or vaccination. The CDC confirmed in February 2023 that XBB.1.5 became the dominant strain in the United States following its emergence at the end of 2022, without translating into an increase in disease severity. Monitoring of XFG follows this precedent, observing its epidemiological behavior to detect any changes in its impact on public health.
What is the Stance of Health Organizations?
The World Health Organization and the U.S. CDC continue to closely monitor the evolution of SARS-CoV-2. In their assessments, like the one published by the WHO Technical Advisory Group on January 11, 2023, on XBB.1.5, they analyze the public health risk based on the genetic characteristics and estimated growth rates. The conclusion for XBB.1.5 was that it could contribute to an increase in case incidences, although confidence in the initial assessment was low as it proceeded from data from a single country.
These organizations do not use nicknames like “Frankenstein” in their official communications. Their focus is on scientific nomenclature and evidence-based recommendations. In this regard, the CDC’s Advisory Committee on Immunization Practices recommended in September 2023 vaccination with an updated monovalent dose of XBB.1.5, as it was shown to generate a broad immune response that protects against circulating lineages. Current vaccines remain effective in preventing severe cases, hospitalizations, and deaths from COVID-19, regardless of the variant. General public health recommendations, such as wearing masks in crowded or poorly ventilated spaces and following exposure, continue to be valid for reducing transmission.
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