Delta variant

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The coronavirus is constantly evolving. Until November 2021, the predominant variant worldwide was Delta, which originated in India.

Different variants have appeared since the initial Wuhan virus, but Delta had the greatest expansion worldwide before the arrival of the Omicron variant.


The Delta variant has the following changes or mutations:

  • Changes in the E484K gene: associated with a reduction in the response of natural and vaccine antibodies.
  • Changes in the L452R gene: favouring infectivity, making the virus more contagious.

These mutations affect the virus spike, which is the part of the virus that binds to the AC2 receptor on human cells. The mutation facilitates binding to the receptor and can therefore infect cells more easily.

This variant is more infective than the Wuhan one and less than Omicron. The R0 of this variant is estimated to be 5, which means each infected person infects approximately 5 more people. It is therefore more transmissible than the Ebola virus and as contagious as chickenpox.

The methods to diagnose the Delta variant of the Coronavirus are the same as for previous variants. Mainly:

Image showing a vial and the instrument for taking the sample and do the antigen test

Rapid antigen tests: Antigen tests in vaccinated people have been seen to be less sensitive, i.e. producing more false negatives, as the viral load in the respiratory tract is cleared more quickly.

Therefore, a person vaccinated who is negative in an antigen test cannot be ruled out as not having SARS-CoV-2 infection via the Delta variant. However, if this person tests positive, the probability that they are really infected is high, since it is a very specific test.

Nasopharyngeal swab

PCR: This is still as effective in detecting people infected with the Delta variant of COVID.

For people vaccinated against COVID-19, the infection rate is reduced by 3, hospitalisation by 4 and mortality by 10.

Studies in the United States of America have shown that 84 of every 100 hospitalisations are unvaccinated people. Therefore, vaccination drastically reduces the probability of having severe illness and being admitted to hospital for a Delta variant infection.

Coronavirus infection produces these clinical situations in vaccinated people:

  • 1 in 2 people (50%) have asymptomatic infection.
  • 1 in 4 people have mild/moderate COVID-19 illness.
  • 1 in 4 people suffer from a serious illness, mostly the elderly or chronically ill.

The following treatments have been shown to be effective for people with moderate to severe infection by the Delta variant:

  • Antiviral medication such as remdesivir, which can prevent hospital admission in almost 90% of cases if administered early. It is also very useful in patients admitted to hospitals with pneumonia who are not intubated or ventilated.
  • Anti-inflammatories, such as dexamethasone or tocilizumab, administered when the so-called "cytokine cascade" occurs, which is an immune response causing great inflammation in the lungs, leading to pneumonia and respiratory failure.
  • Prophylaxis for venous and arterial thrombosis in hospitalised patients: preventive administration of low molecular weight heparin subcutaneously prevents the procoagulant state caused by this infection and therefore possible problems such as thrombosis.  

The standard treatment for severe COVID-19 is currently: administration of remdesivir, corticosteroids such as tocilizumab and prophylactic heparin.

There are two other antivirals in addition to remdesivir that are effective in treating COVID infection in general and the Delta variant in particular. These are Molnupiravir and Nirmatrelvir which are in the process of approval by the European Medicines Agency (EMA). Both reduce hospital admission by 30% and death by almost 90%, especially in individuals over 60 years of age with comorbidity. A single intravenous or subcutaneous dose of neutralising monoclonal antibodies has also been shown to reduce hospital admission rates in 60-80% of cases. All these studies were carried out on unvaccinated people and the results will therefore now have to be validated in vaccinated people.

Global vaccination is of paramount importance to prevent the coronavirus from mutating to escape the natural immune response or vaccine generated immunity.

One vaccine dose protects only 30% against severe disease with the Delta variant, while two doses offer 80% protection. Therefore, as protection is high but does not reach 100%, usual protection measures must also to be maintained.

The vaccines with the highest protection rates are those with mRNA (e.g. Pfizer and Moderna). In contrast, those with the lowest protection rates against infection are viral vector vaccines (e.g. AstraZeneca and Janssen). Therefore, an mRNA vaccine should be received as a third dose.

Studies show that maximum antibody production is reached two weeks after the second dose, and that protection lasts approximately 6 months.

Antibody levels decline more rapidly in people over 60 years of age compared to younger people, which is why it is so important to give booster jabs to older people. It has been observed that if these people are given the third dose, after two weeks the risk of becoming infected is reduced by 10-20 times and of developing a serious illness by up to 20 times.

In addition, people with cancer, undergoing haemodialysis, organ transplant recipients or those receiving immunosuppressive treatment have lower neutralising antibody responses to both doses, and should be prioritised for a third vaccination dose.

In conclusion, vaccination reduces infection and severe disease also for the Delta variant.

Substantiated information by:

Antoni Trilla
Eduard Vieta Pascual
Gema Maria Lledó Ibáñez
Jacobo Sellarés Torres
Josep M. Miró Meda
Josep Maria Peri
Maica Rubinat
Mariona Violan

Published: 12 March 2020
Updated: 12 March 2020

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