SARS-CoV-2 (COVID-19) Variants in Mexico

Abstract

Coronavirus disease 2019 (COVID-19) is an infectious disease caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Due to the virus transmission and propagation since its origin, numerous mutations and variants have occurred. The concern relies on the ability to evade natural immunity and cause infections, even bypassing the immunity generated after the application of vaccines. The World Health Organization classified the variants into “variants of interest” (VOI) and “variants of concern” (VOC). From 2020 to 2021, the VOC variants were the alpha, beta, gamma, and delta types, currently adding the omicron variant. On the other hand, the VOI variants were the eta, iota, kappa, lambda, and mu types. The importance of their study leads to the problem of the possible generation of new waves of contagion, after their appearance, with a high possibility that the immunity known as herd achieved with some previous variant does not become effective.

1. Introduction

The coronavirus disease 2019 (COVID-19) appeared at the end of 2019, and the virus causing the infection was named Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) virus [1].

Coronaviruses come from the Nidovirales order, from the Coronaviridae family and Coronaviridae subfamily, and the latter includes four genera: alphacoronavirus, betacoronavirus, gammacoronavirus, and deltacoronavirus [2, 3, 4]. They infect both mammals (alpha and betacoronaviruses) and birds (gamma and delta coronaviruses) [4]. Currently, seven of them affect humans [5, 6].

Human coronaviruses (HCoV) have been identified for almost 50 years [7]. These are the alpha genus HCoV-229E, HCoV-NL63, and the betacoronavirus HCoV-OC43 and HCoV-HKU1 [8, 9]. The latest betacoronavirus found include the Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) and the Middle East Respiratory Syndrome Coronavirus (MERS-CoV) [8, 9].

The SARS-CoV was identified in Guangdong, China. The reports indicate it spread to 29 countries between November 2002 and July 2003 [10, 11]. On the other hand, MERS-CoV received its name after being identified in Jeddah, Saudi Arabia, in 2012. The outbreak in the Arabian Peninsula reached 27 countries by April 2012 [11].

SARS-CoV and MERS-CoV are of zoonotic origin, and bats are considered the natural hosts, being highly pathogenic since they have caused epidemics of diseases in the last two decades [12, 13, 14, 15].

A new infectious disease caused by a virus recently emerged; likewise, the first genomic sequencing data obtained from this virus did not match the previously sequenced coronaviruses, which indicated the existence of a new coronavirus strain (2019-nCoV) that was later assigned the specific name of SARS-CoV-2 [16, 17]. It was detected after the report of a group of patients with pneumonia of unknown etiology in December 2019 in Wuhan, Hubei, Province of China [18, 19]. Some of the first patients visited a wet shellfish market, where several other wildlife species were sold [19].

Due to the severity caused by this disease and likewise its high potential for worldwide spread, the World Health Organization (WHO) declared it a global health emergency on January 31, 2020 [17]. On February 11, 2020, the Coronaviridae Study Group of the International Committee on Virus Taxonomy named this new betacoronavirus SARS-CoV-2 [20]. On March 11, 2020, the WHO declared a pandemic state worldwide [17].

2. Structure and pathogenesis

SARS-CoV-2 is an enveloped virus with a single-stranded ribonucleic acid (RNA) genome of the beta-coronavirus genus. This RNA helps to encode mainly four structural proteins, these include the spike glycoprotein (S), which is one of the most important in the pathophysiological process; likewise, the envelope protein (E), membrane (M), and nucleocapsid (N); also, such as hemagglutinin esterase (HE) and among other 16 nonstructural proteins such as helicase and RNA-dependent RNA polymerase that help transcription and viral replication [21].

The spike protein (S) of SARS-CoV-2 is responsible for the entry of the virus into the host cell. It is divided by the enzyme furin, which results in two subunits, S1 and S2. The S1 subunit contains a region called the receptor-binding domain (RBD), which binds to the angiotensin-converting enzyme 2 (ACE-2) receptor and thus activates the host cell entry process. The RBD part is considered the main target of neutralizing antibodies after infection; in the same way, it is crucial for vaccine development or another therapeutic plan. On the other hand, in the S1 subunit, there is also a portion named the N-terminal domain (NTD), and it also plays a significant role in antigenicity [22].

The chief transmission mechanism is through the airway, direct contact with viral particles through flugge droplets when coughing, speaking, or sneezing; likewise, through aerosols or by direct contact. Therefore, the onset of the pathology lies with the interaction and fusion of the SARS-CoV-2 virus with the ACE-2 receptors that are mainly expressed in the lungs, allowing entry and, at the same time, the release of this viral RNA inside the cell. Then, the viral RNA initiates the translation of the viral proteins and, in turn, the replication of the genome at the cytoplasmic level, thus developing virions of the SARS-CoV-2 virus, which spread, making the respiratory tract the first line of infection and the virus entry. Therefore, it is the more affected system, resulting in the main respiratory manifestations [21]. The ACE-2 receptors are not only found in the respiratory system; they are widely expressed in the body in different tissues of the apparatus and systems, such as at the cardiovascular, gastrointestinal, and genitourinary levels, among others, leading the organism to show a mild disease to a multisystem compromise or death [2, 3, 21, 23].

There are four main phases in the pathogenic mechanism of COVID-19. These phases summarize the overall pathogenic mechanism of COVID-19, from the initial invasion to the long-term complications associated with the disease [24]. These are:

• Invasion: The SARS-CoV-2 virus uses receptors, such as ACE-2, to recognize and infect various cells, including those that do not express ACE2. It allows it to infect different types of cells in the body.

• Blockade of innate antiviral immunity: During this phase, the virus produces various structural and nonstructural proteins that block the ability of the innate immune system to fight infection. It allows the virus to replicate and evade the body’s initial defenses.

• Activation of viral defense mechanisms: The virus develops mechanisms to evade and suppress the body’s adaptive immune response. It implies passive and active virus protection in the inflammatory centers and continuous virus synthesis in the organism.

• Acute and long-term complications: At this stage, the virus can lead to the spread of variants and trigger acute and chronic complications associated with COVID-19. These complications can include the induction of autoimmune and autoinflammatory responses, as the generation of mechanisms that suppress the immune response and cause multisystem inflammation [24].

3. Evolution of the mutation of SARS-CoV-2 variants

Since the beginning of the COVID-19 outbreak and up to now, the SARS-CoV-2 virus has evolved and has produced some alarming variations. Although nowadays there is a high increase in both natural and vaccine-mediated immunity, many countries are still experiencing resurgences of COVID-19 disease due to the appearance of different and new variants of the SARS-CoV-2 [22].

We must remember and differentiate between mutation, variant, and strain, specifically in the context of the epidemiology of the SARS-CoV-2 virus:

• Mutation: Refers to the change in the virus’s genetic sequence. For example, the D614G mutation is an aspartic acid substitution for glycine at position 614 of the virus spike glycoprotein.

• Variant: Used to describe genomes that differ in sequence from a reference genome. Nevertheless, this term is less precise since two variants can differ in one or several mutations.

• Strain: Strictly speaking, a variant is a strain when it shows a demonstrably different phenotype. It may include differences in terms of antigenicity (ability to be recognized by the immune system), transmissibility (ability to spread between individuals), or virulence (severity of the disease it causes) [25].

In summary, a mutation is a change in the genetic sequence, a variant is a genome that differs from a reference genome, and a strain is a variant that shows demonstrable phenotypic differences. These distinctions are important for understanding the epidemiology and characteristics of the SARS-CoV-2 virus.

Mutations often offer evolutionary benefits at the molecular level, such as increased recognition by the target cell, more effective entry into cells, or the ability to evade the immune system, tend to persist and can establish themselves in each virus lineage [26].

We refer to clinically and epidemiologically significant variants as those that, due to one or more mutations, can evade natural immunity and cause reinfections, evade immunity generated after vaccination and cause infections in vaccinated persons, evade the effectiveness of treatments such as antivirals, monoclonal antibodies, and convalescent plasma; on the other hand, they influence the severity of the disease with greater virulence, alter the transmission dynamics with a greater capacity to infect, and affect the accuracy of diagnostic tests [27].

RNA viruses, such as coronaviruses, come to present a considerably higher evolution rate than DNA viruses. The reason is its high susceptibility to replication errors caused by RNA polymerase or reverse transcriptase; furthermore, the higher viral population and its rapid replication rate also contribute to this accelerated evolutionary process [24, 28]. Although viruses commonly have a high mutation rate, SARS-CoV-2 has an enzyme – the RNA-dependent RNA polymerase – able to correct mistakes. This feature could explain why SARS-CoV-2 has a lower mutation rate than other RNA viruses [27]. However, the mutations that manage to emerge depend on a process of natural selection: only those that give the virus greater transmission capacity or the ability to evade the immune system persist in the population. Genetic analysis of the virus at the epidemiological level allows us to observe this evolution [27].

4. New variants and their nomenclature

As SARS-CoV-2 has been transmitted and spread, numerous mutations and variants have occurred. Over time, these have emerged and, in turn, have been organized and classified [27]. Given their classifications, the genetic changes of the virus, the increase in the speed of contagion, and aggressiveness are considered, besides the reduction in the effectiveness of public health measures, diagnoses, vaccines, and available treatments [26].

The UK Institute of Public Health has its own terminology, calling variants of concern those having a significant epidemiological impact. They also use the term Variants Under Investigation (VUI) to refer to those that can become variants of concern (VOC). The United States Centers for Disease Control (CDC) and Prevention and the World Health Organization (WHO) have adopted the definition of “variants of care” and have introduced the term “variants of interest” (VOI) -with an interpretation equivalent to VUI- and recommend its use globally [27].

In June 2020, the WHO Task Force on Viral Evolution was established, specifically focused on SARS-CoV-2 variants, their phenotype, and their impact on control measures. This group later became the Technical Advisory Group on the Evolution of the SARS-CoV-2 Virus. At the end of 2020, with the appearance of variants that represented a greater risk to public health worldwide, the WHO began to characterize some of them as VOI and VOC with the aim of the objective of setting priorities in surveillance and research globally and guiding the response to COVID-19. In May 2021, WHO began assigning simple, easy-to-pronounce names to main variants. In March 2023, WHO updated its surveillance system and working definitions for variants of concern, variants of interest, and variants under monitoring (VUM) [29].

5. SARS-CoV-2 variants

5.1 Alpha (B.1.1.7)

In the United Kingdom, in December 2020, the detection of a new variant of the SARS-CoV-2 virus, known as B.1.1.7 according to the Pango lineage nomenclature system, was reported. The WHO designated it the alpha variant. It was the first VOC identified. Retrospective analysis revealed that this VOC was already in circulation in September 2020 in the UK. The B.1.1.7 lineage spread rapidly in the UK and became the predominant variant in early 2021. It has subsequently spread successfully to most European countries. As of November 2021, local transmissions of this lineage have been recorded in 175 countries [30].

In Mexico, the B.1.1.7 lineage was identified for the first time in December 2020. Since then, a gradual increase in its circulation frequency was observed, reaching its peak in May 2021, but without becoming the predominant variant [30].

The data suggests that this variant is between 43% and 90% more contagious than previously existing lineages in the UK. Concerning the severity of the disease, although some reports have not shown clear evidence of an increase in mortality associated with the alpha variant, others have shown its connection with more severe diseases [22].

5.2 Beta (B.1.351)

The beta VOC variant shows three RBD mutations (N501Y, E484K, and K417N), as well as some NTD mutations, except for the 69/70 deletion. It was identified in South Africa in October 2020, and cases have since been detected elsewhere outside South Africa. There is no conclusive evidence to suggest increased mortality associated with this variant. Nevertheless, some reports indicate that the E484K mutation may affect neutralization by various monoclonal antibodies, including casirivimab, bamlanivimab, and etesevimab. In addition, the beta variant has shown higher resistance to the neutralizing activity of convalescent plasma and sera from individuals immunized with the mRNA-1273, BNT162b2, and AZD1222 vaccines [22, 28].

5.3 Gamma (P.1)

RBD mutations were detected in the gamma variant, which was cataloged as VOC. On January 6, 2021, the gamma variant was identified in four Japanese citizens who arrived in Tokyo after traveling to the Amazonian region of Brazil a few days earlier. This variant caused an increase in infection in the Manaus region of Brazil, where most of the population had already been infected by SARS-CoV-2. This variant is associated with increased transmissibility, risks of reinfection, and mortality. Like the beta variant, the gamma variant shows resistance to neutralization by various monoclonal antibodies, convalescent plasma, and vaccine sera [22, 28, 31].

5.4 Delta (B.1.617.2)

The delta variant, a VOC, was identified in India in early 2021. This variant exhibits the L452R mutation in the RBD and the P681 mutation in the furin cleavage site. In addition, it has several additional mutations in the spike protein (T19R, R158G, T478K, and D950N), as mutations in the orf3, orf7a, and nucleocapsid genes. The delta variant quickly displaced the alpha variant in multiple countries and became the dominant VOC globally. The delta variant has increased transmissibility due to possible mechanisms such as a higher infectious viral load, a longer virus shedding duration, and a higher reinfection rate due to antibody escape. The susceptibility of the delta variant to convalescent plasma and the sera of persons vaccinated with BNT162b2 and AZD1222 is reduced. Nevertheless, one study showed that BNT162b2 offers higher protection against the delta variant than AZD1222. In addition, the delta variant can resist bamlanivimab and some other monoclonal antibodies (mAbs) [22, 28, 31].

5.5 Omicron (B.1.1.529)

The omicron variant of the SARS-CoV-2 virus was first detected in South Africa in November 2021 and has spread to more than 50 countries. Omicron has different subvariants, BA.1 being the most transmissible and globally dominant, displacing the delta variant. BA.2 then emerged and replaced BA.1 in some countries. In addition, other subvariants such as BA.4/5 and BA.2.12.1 have been identified, which have a higher transmission capacity than BA.2 [22].

Omicron has more than 30 mutations in its spike proteins, some of which can affect the sites where antibodies bind to neutralize the virus. These subvariants have shared mutations, such as E484, K417N, T478K, N501Y, and P681H, associated with increased transmissibility and antibody evasion. However, each subvariant also has unique mutations [22].

Studies have shown a decreased ability of vaccine and convalescent sera to neutralize omicron subvariant BA.1. However, sera from persons vaccinated with boosters or previously infected showed antibodies that can still neutralize BA.1. The efficacy of vaccinations and boosters is similar for BA.1 and BA.2 [22, 32].

Limited cross-reactions have been observed between the different subvariants of omicron and other coronaviruses. Some therapeutic monoclonal antibodies, such as bamlanivimab, imdevimab, casirivimab, and etesevimab, have decreased efficacy against omicron subvariants. However, sotrovimab maintains some activity, albeit reduced, against BA.2, BA.4/5, and BA.2.12.1. Other monoclonal antibodies, such as tixagevimab/cilgavimab and adintrevimab, are partially active against BA.2 and BA.4/5 [22, 33].

In summary, the omicron variant of SARS-CoV-2 has generated different subvariants with mutations in spike proteins, which may affect the neutralization capacity of antibodies. Even as vaccines and therapeutic antibodies show less efficacy against omicron, boosters, and prior infection may provide only some protection against the identified subvariants.

6. Epidemiology of COVID-19 in Mexico

The global impact caused by the pandemic has been uneven in different parts of the world. Latin America has experienced a high impact due to the disease, presenting higher mortality rates than Western European countries. Mexico has been especially vulnerable due to underlying risk factors in its population, such as cardiovascular diseases such as dyslipidemia, hypertension, and type 2 diabetes. This combination of factors has generated greater severity, where poverty and limiting social factors, such as access to medical care, have been determining factors in the epidemiological outcome [26].

In May 2020, a mutation in the SARS-CoV-2 spike protein known as D614G occurred, which became prevalent in virus genomes worldwide. This mutation gave rise to lineage B – named as in the Pango nomenclature – which has remained the predominant lineage in the phylogenetic landscape. This lineage presents a greater infection capacity, competitiveness, viral load, and transmission in human and animal models. So far, five main VOCs have been identified at different stages of the pandemic in Mexico; alpha, beta, gamma, delta, and omicron. However, the omicron lineage is the most dominant, presenting more than 50 mutations, of which more than 30 are in the spike (S) protein [26].

In the last update on the epidemiology of COVID-19 in Mexico at the national level, updated in July 2023, published by the General Directorate of Epidemiology, 7,633,355 confirmed cumulative cases were reported. The distribution by sex of the confirmed cases was 53.66% for women and 46.34% for men. The general hospitalization percentage was 9.57%. The most frequent and chief comorbidities are hypertension at 11.90%, obesity at 9.59%, diabetes at 8.74%, and finally smoking at 5.41% [34].

On the other hand, in negative cases, a total of 11,638,267 have been registered. In suspected cases with a total of 830,243, recovered cases with 6,885,378, and active cases with 3558 [34].

7. SARS-CoV-2 (COVID-19) variants in Mexico

Despite the constant work against COVID-19 in the public health and research context, there have been severe resurgences in the number of cases, where the different variants of the virus are currently found, with the omicron variant predominating. Keeping infected people isolated from the onset of symptoms is one of the best alternatives since scientific findings suggest a shorter transmission and incubation period than other variants [35]. Over time, all kinds of information have changed because all viruses change with time, as does SARS-CoV-2, the virus that causes COVID-19 [29].

Although the COVID-19 pandemic began at the end of 2019 and the beginning of 2020, the Mexican government, through the Secretary of Health of Mexico, began the analysis and specific report of the genomic surveillance of the SARS-CoV-2 virus in Mexico’s National and State Distribution of variants since August 30, 2021, and which is currently under development and in constant updating report [35].

From 2020 to 2021, the VOC variants were classified with the alpha, beta, gamma, and delta types; while, to the VOI variants with the eta, iota, kappa, lambda, and mu types. Besides, the genomic analysis in Mexico during 2020–2021 COVID-19 was documented through the global exchange initiative from genomic surveillance data for influenza viruses and SARS-CoV-2 (GISAID). Until October 18, 2021, up to epidemiological week 40, 32,081 sequences were reported [35].

The WHO classification of the variants was maintained early in 2022. Nevertheless, at the same time, a different variant named “omicron” was identified. Therefore, during the year, the omicron variant was classified as VOC with its respective classification with Subvariants of omicron under monitoring (from November 20, 2022) BA.5, BA.2.75, BA.4.6, XBB, and BA.2.3.20. VOI and VUM were maintained and, as additional data, the variants BQ.1, BW.1, and DL.1 were reported in this type [35].

In turn, during the year 2022, there was a high difference between the beginning and the end of the year. From April 4, 2022, to December 30, 2022, the reported sequences by GISAID increased from 57,823 to 81,429 [35].

Regarding 2023, from January 16, 2023, to May 4, 2023, the number of sequences reported by the GISAID increased from 81,914 to 87,447 [35].

Table 1 shows the information published through the global initiative for sharing data on the GISAID. It is worth mentioning that, for greater understanding, the VUM reports were excluded since they are constantly modified daily. The order by prevalence in 2021 is the following: delta, gamma, alpha, and beta. During 2022, the most prevalent VOCs were delta, with 25,434, followed by omicron, with 23,681. On the other hand, during 2023, the only predominant VOC was omicron, with a total of 34,499. The only exception added as a VOI was the last reported on May 4, 2023, because a type of lineage descendants of omicron reported as XBB.1.5 and XBB.1.16.

Year Date	Kind of variants	Variant name	Total National from each variant
From August 30 to October 18, 2021	VOC	Alpha	1759
		Beta	19
		Gamma	2711
		Delta	12,697
From April 4 to December 30, 2022	VOC	Delta	25,434
		Omicron	23,681
From January 16 to May 4, 2023	VOC	Omicron	34,499
From May 4 to June 30, 2023	VOI	Omicron (XBB.1.5)	1032
		Omicron (XBB.1.16)	1
Total			101,833

Table 1.

Summary of the evolution of the variants of concern of COVID-19 in Mexico.

VOC: Variants of Concern, VOI: Variants of Interest.

Source: With data obtained from the public database GISAID https://www.gisaid.org/

8. Epidemiological impact

The mutation D614G was identified in January 2020. Two months later, it came to present greater infectivity. In June, it became the predominant one in the world. Currently, 100% of the active variants have this mutation [27]. Thus, the importance of the impact of these variants and the possible generation of new waves of contagion. After their appearance, the immunity achieved with some previous variants could not be effective [27].

9. Vaccines and new variants

As we continue to learn more about this new virus, it remains an unprecedented event in world history [36]. The emergence of the pandemic led to the discovery of ways to achieve herd immunity and reduce the harmful effects of COVID-19 through vaccines. Remembering that the development of vaccines must go hand in hand with genomic surveillance [27]. Nowadays, these efforts have shown valuable results and are under implementation in all nations. Because it was necessary to synthesize the evidence of the effectiveness of vaccines against VOCs of SARS-CoV-2, various studies were carried out [36].

Baoqi Zeng et al. [37] conducted several pieces of research, including randomized controlled trials (RCTs), cohort studies, and case-control studies that evaluated vaccine effectiveness over our continuing-study variants of concern (alpha, beta, gamma, delta, or omicron), making a cut until March 4, 2022.

The variants of concern have mutations in their spike protein. Zeng B et al. [37] found that the complete vaccination of the COVID-19 vaccines was effective against the alpha, beta, gamma, delta, and omicron variants, with an effectiveness of 88.0, 73.0, 63.0, 77.8, and 55.9%, respectively. Also, it was found that the delta and omicron variants presented 95.5 and 80.8%, respectively, of effectiveness with the booster dose. Finally, mRNA vaccines (BNT162b2 or mRNA-1273) have higher effectiveness against variants of concern than other vaccines [37].

In other in vitro studies involving the Pfizer and AstraZeneca vaccines, decreased antibody titers against the delta variant were shown [27].

10. Signs and symptoms of COVID-19

The signs reported by individuals suffering from COVID-19 differ between those experiencing mild symptoms and those facing more severe illness. Symptoms can appear within 2 to 14 days after contact with the virus. Symptoms can vary in intensity, from mildly to severely [38, 39].

The most common symptoms of COVID-19 are the following:

• Fever

• Shaking chills

• Sore throat

Other accompanying symptoms:

• Muscle pain

• Severe fatigue or tiredness

• Severe runny, stuffy nose, or sneezing

• Headache

• Eye pain

• Dizziness

• New and persistent cough

• Tightness or pain in the chest

• Respiratory distress

• Hoarsely

• Numbness or tingling

• Nausea, vomiting, abdominal pain/stomachache, or diarrhea

• Loss of appetite

• Loss or change of taste or smell

• Difficulty breathing.

Symptoms of severe illness from COVID-19 and needing urgent medical attention include:

• Difficulty breathing, especially at rest, or an inability to speak in full sentences.

• Confusion

• Drowsiness or unconsciousness

• Persistent pain or pressure in the chest

• Cold or clammy skin or pale or bluish skin

• Loss of speech or mobility.

This previous enumeration does not cover all the possible signs. Symptoms may change their presentation with new variants of COVID-19 and may differ depending on vaccination status. The CDC continually updates this list as more COVID-19 information piles up. Older people and those with preexisting conditions such as heart disease, lung disease, or diabetes are at higher risk of experiencing severe complications from COVID-19 [38, 39].

Regarding Mexico, Loza A. et al. [40] reported four waves of COVID-19 from March 2020 to March 2022. Table 2 shows the data about the predominant variants, the clinical manifestations, and figures about hospitalization and deaths. It is noted that hospitalization decreased with each wave, and so did the case fatality rate.

Wave	Predominant variants	Confirmed cases	Case fatality rate (%)	Hospitalizations (%)	Clinical data predominant
First; (March to September 2020)	B.1,; B.1.1, B.1.1.222	809,387	12.3	25.1	Headache; Fever; Myalgia; Arthralgia; General malaise; Odynophagia
Second; (September 2020 to April 2021)	B1.1.222; B.1.1.519	1,538,110	8.7%	16.4%	Headache; Fever; Odynophagia; Myalgia; Arthralgia
Third; (November 2021 to March 2022)	Alpha; Delta; Gamma	1,439,463	4.2	9.8	Cough; Fever, Headache; Rhinorrhea; Odynophagia
Fourth (December 2021 to March 2022)	Omicron BA.1	1,722,625	1.2	3.4	Cough; Headache; Fever; Odynophagia; Rhinorrhea

Table 2.

Waves of COVID-19 in Mexico (March 2020–March 2022) by predominant variants and clinical data.

Source: Taken from [40].

11. Conclusion

SARS-CoV-2 has generated different variants. These variants have been characterized as having specific genetic changes that may affect their transmissibility, disease severity, response to vaccines, and available treatments. Some variant has been shown to be more transmissible than the original strain of the virus and has raised global concerns due to their ability to spread rapidly.

The study of new SARS-CoV-2 variants supports the public health efforts for COVID-19 pandemic containment. It provides valuable information about the possible consequences of new scenarios. It is important to note that besides transmissibility, clinical manifestations play a crucial role in assessing the potential impact of new SARS-CoV-2 variants since they can cause a significant strain on health services. In the case of Mexico, the number of cases grew, but the CFR and the percentage of hospitalizations were lower in each successive wave driven by the predominant variants.

Finally, COVID-19 is a subject of active and constantly evolving research. Nowadays, additional research is underway to understand all the mechanisms involved and thus develop more effective and specific treatments. Although there is currently high natural and vaccine-mediated immunity, outbreaks continue to occur in some countries due to the different and constant variants of SARS-CoV-2.

Conflict of interest

The authors declare no conflict of interest.

Funding

None to the review.

The University Autonomous of Guadalajara will support the Open Access fee.