Paris Study: Highest Viral Loads among Delta Variant Carriers

Viral loads are the best predictor of death in COVID-19, according to research. That study can be found here: SARS-CoV-2 Viral Load: Best Predictor of COVID-19 Death.

A new study shows that people with COVID-19 infected with the Delta variant  COVID-19 have the highest viral loads compared to other people with other variants.

The study, The Delta SARS-CoV-2 variant, has a higher viral load than the Beta and the historical variants in nasopharyngeal samples from newly diagnosed COVID-19 patients is available in the October 2021 edition of the Journal of Infection.

The study obtained samples from four laboratory hospitals in the Paris area (Pitié-Salpêtrière, Bichat-Claude Bernard, Saint-Antoine/Trousseau, and Avicenne hospitals) at their epidemic peak.

At their investigation, the Delta variant accounts for 90% of new cases in France.

How did they know the viral loads?

Reverse-transcription polymerase chain reaction (RT-PCR) was the test done to determine the viral loads. RT-PCR is collected with nasal swabs.

The viral load was determined using the cycle threshold (Ct) of the open reading frame 1ab (ORF1ab) and nucleocapsid (N) target genes. ORF1ab and N genes are parts of the spike protein of the SARS-CoV-2.

The cycle threshold is a measure of how many viruses are present. The lower the cycle threshold, the higher the viral load.

If the number of viruses is fewer, more cycles have to be done for the test to become positive. Fewer viruses need a higher cycle threshold for the test to become positive.

The variants measured were the Delta, Alpha, the Beta, and the historical 20A.EU2. A total of 738 RT-PCR samples collected from nasal swabs were sequenced.

The median age is 51 years (27-67), 48% men, 332 historical SARS-CoV-2, 249 Alpha, 98 Beta, and 59 Delta variants.

The results

  1. The Delta variant has a  viral load ten times higher than the historical variants.
  2. They also found a two-fold difference in the ORF1ab viral load between the Delta and Alpha and Beta variants.
  3. Using the N gene, the Delta variant is 5-fold higher in viral load than the historical variants.
  4. There is a significant 2.5-fold higher difference in viral load levels between the Delta and Beta variants.
  5. No statistical difference was found between the Delta and the Alpha variants.

According to one report, the transmission rate of the Delta variant is 40-60% more transmissible than the Alpha variant.

Why is the Delta variant more infectious?

The Delta variant has three key mutations in its spike protein. The L452R,
T478K and P681R. These mutations change the shape of the receptor-binding protein that prevents the attachment of neutralizing antibodies. 

Amino acid mutations of SARS-CoV-2 Delta variant plotted on a genome map of SARS-CoV-2 with a focus on Spike. Note the L452R, T478K, and P681R. Source: Wikipedia

Aside from making the virus more infectious, these mutations prevent the antibodies generated by current COVID-19 vaccinations from neutralizing the Delta variants. The non-neutralization of viruses creates a condition called an immune escape.

Immune escape can explain why the Delta variants continue to replicate unabatedly in the nasal cavity and show a high viral load when the nasal swab is done.

Read more about immune escape here: Immune escape: The reason the vaxxed get COVID-19.

This study echoes the findings of a similar study done in Vietnam where vaccinated workers have viral loads 251 times higher compared to the unvaccinated. The spread of the Delta variant among vaccinated Health Care Workers in Vietnam.

High viral loads are nothing to sneeze at. Although most patients with the Delta variant are asymptomatic and have mild symptoms, those who present to the hospitals with a high viral load are predicted to have a high mortality rate. It is discussed here: SARS-CoV-2 Viral Load: Best Predictor of COVID-19 Death. 

ADE may explain the high mortality rates: Antibody-dependent enhancement (ADE) can happen to Delta Variant COVID-19  and What is Antibody-Dependent Enhancement and why should you care.

Prevention and early treatment are keys to prevent COVID-19 deaths.

Knowledge about Covid-19 is rapidly evolving. Information may update as new studies are made. Stay current by subscribing. Feel free to share and like.

Don’t Get Sick!

Reference:

  1. Teyssou et al. The Delta SARS-CoV-2 variant has a higher viral load than the Beta and the historical variants in nasopharyngeal samples from newly diagnosed COVID-19 patients. LETTER TO THE EDITOR| VOLUME 83, ISSUE 4, E1-E3, OCTOBER 01, 2021
  2. SPI-M-O: Consensus Statement on COVID-19

Image credit: Delta protein sequence By Stanford HIVDB Team, PhiLiP – https://covdb.stanford.edu/page/mutation-viewer/, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=106842398

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