Characterization of SARS-CoV-2 mutants in unvaccinated and vaccinated U.S. military

Since the discovery of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), several viral variants have emerged, some of which have shown superior pathogenicity and infectivity compared to the original strain. rice field.

The World Health Organization (WHO) has made these more toxic strains of SARS-CoV-2 infectious, mutated, toxic, and of concern, depending on their ability to evade the immune response generated. Classified as VOC) or mutant strain of interest (VOI). By immunization or natural infection.

study: Genomic and virological properties of SARS-CoV-2 mutants in a subset of unvaccinated and vaccinated US military personnel. Image Credits: Emily C. McCormick / Shutterstock.com

Background

To date, five SARSs including B.1.1.7 (alpha), B.1.351 (beta), P.1 (gamma), B.1.617.2 (delta), and B.1.617.2 (delta). -CoV-2VOC has been identified. B.1.1.529 (Omicron) strain. Recently, the Omicron mutant has become a major circulating strain in most countries around the world.

Prior to the emergence of the Omicron variant, scientists characterized the delta variant as more contagious than the alpha variant. To this end, studies have shown that delta variants have caused increased hospitalization rates among unvaccinated individuals.

With the advent of SARS-CoV-2 VOCs, there are increasing reports of vaccine breakthrough infections (VBIs). Real-time reverse transcription-polymerase chain reaction (qRT-PCR) has proven to be very efficient in detecting COVID-19, but one of the limitations of this assay is the viral ribonucleic acid rather than the virus itself. Is to detect. This is problematic because the viral load estimated by qRT-PCR does not always correlate with the amount of viable virus in a particular sample.

Within laboratory settings, scientists detect infectious viruses In vitro Virus culture in susceptible cell lines.Although this method is effective and provides insights related to Viral sheddingIt is labor intensive and requires a biosafety level 3 (BSL-3) facility when handling SARS-CoV-2.

In general, Vero cells and their subclones, such as Vero E6 cells expressing human transmembrane serine protease 2 (TMPRSS2), Commonly used for culturing SARS-CoV-2. The plaque or median tissue culture infection level (TCID50) assay is used to quantify viable virus.

Several studies have described methods for measuring the amount of viable virus released by individuals infected with various SARS-CoV-2 variants, but with vaccinated individuals and vaccinated individuals. Further research is needed to characterize the viral levels of individuals who do not. This is essential because different studies follow different methods and focus on different samples from different geographic locations.

About research

New Medical frontier In the study, researchers discuss the genomic and virological properties of SARS-CoV-2 variants among unvaccinated and vaccinated US military personnel. Authors gathered from a cohort of U.S. military personnel and beneficiaries stationed worldwide as part of the Department of Defense Health (DHA) Global Emerging Infection Surveillance (GEIS) program from March 2020 to early November 2021. The nasal swab sample was evaluated.

SARS-CoV-2 positive samples were determined, followed by next-generation sequencing. We analyzed the subset to estimate the viable virus.

Investigation result

A significant proportion of VBI cases in the current study were associated with delta mutations. Researchers have observed that the increased infectivity of this variant is partly due to increased viral shedding.

Interestingly, in VBI, the authors reported a 50-fold increase in viable virus in nasal swab samples from cases with delta mutants compared to cases containing other mutants. .. Similarly, nasal swab samples from VBI containing Delta showed a 40-fold increase in viable virus compared to unvaccinated personnel infected with other variants.

Pango strain of circulating SARS-CoV-2 strain in the US military before and after the implementation of EUA vaccine. (A) Monthly distribution of Pango strains for all samples, (B) Distribution of delta mutant sub-strains by month, (C) Stacked graphs showing all strains by month, and (D) Monthly distribution. Stacked graph showing delta mutant sub-strains.

At that time, no individual was vaccinated because no vaccine was approved by the world’s regulators. The findings from this study are consistent with previous studies involving the rest of the United States, where the delta variant was the predominantly circulating strain.

Scientists have reported that the delta mutant contains the R203M mutation, while the Omicron mutant contains the R203K mutation. This may be the reason for the increased fitness of these mutants. Previous studies have shown that samples from individuals infected with the delta variant have longer periods of increased viral RNA levels and viral shedding compared to samples obtained from people infected with other variants. increase.

Researchers also observed similar levels of viral RNA from vaccinated and unvaccinated individuals. In the future, more research is needed to determine the duration of viral shedding and viral load associated with the Omicron mutant.

Scientists analyzed the results across vaccine makers and found significantly higher levels of viable virus in samples from Pfizer and Johnson & Johnson vaccinated individuals. It was found that these individuals experience more VBI due to delta mutation infection than unvaccinated personnel with non-delta infection.

Conclusion

One of the limitations of this study was the lack of availability of clinical sample metadata. This hampered the proper interpretation of the results regarding age, pre-existing conditions, and differences in the number of days since the onset of exposure or symptoms.

In addition, the survey cohort included young military personnel between the ages of 18 and 40 who needed to maintain proper physical condition for their duties. Therefore, lack of diversity can also lead to biased results.

Current studies characterize the SARS-CoV-2 genome and the viable viral titers of all new SARS-CoV-2 variants isolated from unvaccinated and vaccinated personnel. The importance is emphasized.