A variant has one or more mutations that differentiate it from other variants in circulation. They have demonstrably different phenotype difference in terms of antigenicity, transmissibility, and virulence. Center for Disease Prevention and Control, (CDC) Atlanta has classified the SARS-CoV-2 variants into three categories— variants of interest, variants of concern and variants of high consequences. World Health Organization (WHO) has classified into variants of interest and variants of concern.

Variants of interest (VOI): Variants of interest of SARS-CoV-2 has been defined by having the following two characters:

1. SARS-CoV-2 with specific genetic markers that are predicted to affect the virus characteristics in terms of transmission, diagnostics, disease severity, immune, diagnostic or therapeutic escape.

2. Identified as a cause of significant community transmission or multiple COVID-19 clusters, in multiple countries with increasing relative prevalence alongside increasing number of cases over time or other apparent epidemiological impacts to suggest an emerging risk to global public health.

 Examples of VOI is shown in Table1.

Table1. Variants of interest

Variants of concern (VOC): Variants of concern of SARS-CoV-2 has been defined by having the following characters in addition to the attributes of VOI:

 • Evidence of reduced effectiveness to treatment.

• Evidence of reduced effectiveness to vaccine.

• Evidence of significant decreased neutralization by antibodies generated during previous infection.

• Evidence of increased transmissibility.

• Evidence of increased disease severity.

• Evidence of escaping diagnostic detection.

The example of VOC is shown in Table 2.

The properties imparted by different mutations in variants are given in Table 3.

Table2. Variants of concern

Table3. Properties of important mutations

Table3. Properties of important mutations (contd.)

Characteristics of variants of concern Alpha variant: Known for its high transmissibility and higher severity.

• Mutations: N501Y, D614G, P681H.

• Highly infectious: 70% increased transmission.

 • Higher severity with higher case fatality.

 • No impact on susceptibility to monoclonal antibodies.

• Minimal impact on neutralizing antibody by convalescent serum.

 • Minimal impact on neutralizing antibody by post-vaccination serum: Almost by all available vaccine.

Beta variant (B.1.351: South Africa): Known mostly for its immune evasion property.

• Mutations: D614G, N501Y, E484K, K417N.

• Higher infectivity: Shows 50% increased transmission.

• Escape neutralization: Significant decrease in susceptibility to monoclonal antibodies.

• Reduced neutralization by convalescent sera and post-vaccination sera.

 • Astra Zenecea (ChAdOx1nCoV-19-AZD1222): No protection against mild-mod infection. • Sputnik: Mod-marked reduction in neutralization.

• Moderna and Pfizer: 6.5–8.6-fold reduction in neutralization.

Gamma variant (P1: Brazil): Known mostly for its immune evasion property

• Mutations: K417T, E484K, N501Y, D614G, H655Y.

• Significant decrease in susceptibility to monoclonal antibodies.

• Reduced neutralization by convalescent sera and post-vaccination sera.

Delta variant: Known for its high transmissibility, higher severity and immune evasion.

Initially B.617 pango lineage was labelled as “Delta variant”. It has 3 sub-lineages— B.1.617.1, B.1.617.2, and B.1.617.3. Of the three, 1 and 2 are more transmissible. Currently, B.1.617.2 is named as “Delta variant”. It is presently spreading all over the globe and has been detected in more than 90 countries and has been declared as National Variant of Concern in UK.

Initially it was popularly called “Double mutant” due to presence of E484Q and L452R mutations which are responsible for their immune evasion and transmissibility proper ties. However, evidence showed, whether combinedly present or singly present, these mutations show equal fold of immune evasion. Thus, refuting the labelling of double mutant. The presence of mutation P681R in this variant has shown enhanced capacity of cell-cell fusion and syncytium formation indicating that it is responsible for higher pathogenicity.

Delta-AY.1 (delta with K417N): Delta variant containing the mutation K417N is popularly known as “Delta Plus” though such labelling is not made by WHO or CDC. The mutation K417N is also present in beta and gamma variants and responsible for immune escape property of the variant. It has two clades AY.1 and AY.2, of which the prior one is inter nationally distributed. Delta variant with 417N mutation is already detected in 10 countries including India.

Important properties of delta variant:

 • Highly transmissible:

– Transmissibility: 50% higher than aplha and 97% higher than other VOC/VOI

– Predominant in India, UK and Moscow, Russia

– Secondary attack rate: Higher than alpha (11 vs 8%)

• Impact on severity: Mostly due to P681R mutation

– More severe– Higher viral load in lungs and severe lung damage in experimental animal

– Fusion and syncytium formation

 • Effect of monoclonal antibody (mAb): Reduced neutralization by approved mAb for therapy (bamlanivimab, etesevimab, casirivimab, and imdevimab).

• Effect of convalescent sera: Sixfold less as compared to alpha variant.

Variants of high consequence (VHC): Variants of high consequence have the following criteria in addition to the features of VOC:

• Significant reduction in vaccine effectiveness

• Significant failure to approved therapeutics

• Failure to be detected by the diagnostics

• More number of severe diseases and hospitalizations

So far, no variants have been labelled as Variants of high consequence.

Effect of vaccine: It has been shown that in fully vaccinated general population or vulnerable population the risk of infection is much lower as compared to those who are partially or not vaccinated.

Several studies have shown 3 to 8-fold reduction of neutralization by mRNA vaccines (Moderna and Pfizer) and about twofold reduction in neutralization as compared to B.1 (D614G) and B.1.1.7 (UK strain) by Covaxin and Covishield.

Vaccine efficacy against symptomatic disease due to delta variant is less as compared to that of alpha variant. This is more so after the first dose of vaccine (33% in delta variant vs 51% in alpha variant). Whereas, the efficacy after the second dose is almost similar against both the variants and more than 80% in both when tested with Pfizer and AstraZeneca.

Vaccine efficacy against hospitalization due to either delta or alpha variant is similar and about 75% after the first dose and more than 90% in both variants after the second dose when tested with Pfizer and AstraZeneca.

Durability of vaccine effect: Johnson and Johnson single-shot COVID-19 vaccine shows neutralizing antibody activity against the delta (B.1.617.2) variant. Both humoral and cellular immune responses lasted through at least eight months.

Effect of herd immunity: More than 90% vaccine-induced herd immunity is required to keep a check on delta variant. In general, higher vaccine coverage is required in case of higher transmissibility of the virus variants and poor vaccine efficacy.

Strategies to reduce the emergence of variants:

a. Vaccine coverage should be >90% with complete dose and with minimum gap between first and second doses and should be done rapidly in order to reduce the population of partially/non-vaccinated individuals.

b. In addition to this, care should be taken to reduce the duration of virus replication particularly in immunocompromised individuals where usually there occurs delay in virus clearance due to poor immunity. Prolong replication gives scope for mutation.

 c. Use of antibody-based therapy such as monoclonal antibodies, plasma therapy where their efficacy is limited or un demonstrated efficacy should be avoided as partially effective measures may facilitate the evolution of variants.

اخر الاخبار

اخبار العتبة العباسية المقدسة

قسم شؤون المعارف يطلق دورة (صفات الشيعة) لعدد من ملاكات العتبة العباسية المقدسة

الهيأة العليا لإحياء التراث تبحث تعزيز التعاون المشترك مع مركز الإمام الباقر (عليه السلام) في إيران

جامعة الكفيل تكرِّم طلبتها المتميزين من ذوي الاحتياجات الخاصة

فريق طبي في مستشفى الكفيل يجري عملية ناجحة لطفل يعاني من تشوّه ولاديّ بالنخاع الشوكي

المزيد

الآخبار الصحية

خصوصا مع تقدم السن.. 6 سلوكيات يومية قد تدمّر صحتك

فاكهة خضراء.. علاج طبيعي فعّال للإمساك واضطرابات الهضم

روسيا تبدأ أولى التجارب السريرية للقاح واعد ضد السرطان

كنز غذائي على طبقك.. ماذا تفعل السبانخ بجسمك؟

المزيد

الآخبار التكنلوجية

رصد نوع نادر من القطط في تايلاند للمرة الأولى منذ عقود

روسيا تخطط لإقامة محطة نووية في القمر خلال العقد المقبل

كيف قاد إيلون ماسك حملة "غروك" لاختراق عرش الذكاء الاصطناعي

ألتمان: الذكاء الاصطناعي سيتجاوز البشر في 2026 !

المزيد

مواضيع ذات صلة

Polyomaviruses

Picornaviruses

Parvoviruses

Paramyxoviruses

Properties of Paramyxoviruses

Influenza Virus Replication

Antigenic Drift and Antigenic Shift

Structure and Function of Neuraminidase

Complications of COVID-19

Clinical Features of SARS-CoV-2 and COVID-19

Modes of Transmission SARS-CoV-2 and COVID-19

Papillomaviruses