Health and Fitness

The relative dynamics of infection with the Delta and Omicron SARS-CoV-2 variants in aged and young Syrian hamsters

In a current research posted to the bioRxiv* preprint server, researchers demonstrated the relative pathogenicity of extreme acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron and Delta variants of concern (VOCs) in Syrian hamsters.

Study: Comparative pathogenicity of SARS-CoV-2 Omicron and Delta variants in Syrian hamsters mirrors the attenuated clinical outlook of Omicron in COVID-19 irrespective of age. Image Credit: stock_shot/Shutterstock
Study: Comparative pathogenicity of SARS-CoV-2 Omicron and Delta variants in Syrian hamsters mirrors the attenuated scientific outlook of Omicron in COVID-19 no matter age. Image Credit: stock_shot/Shutterstock


Coronavirus illness 2019 (COVID-19) continues to devastate the world with the fixed emergence of novel strains of SARS-CoV-2. It has brought on repeated cycles of infections throughout the globe. The SARS-CoV-2 Omicron VOC that emerged in late 2021 had over 50 mutations relative to the reference pressure, and 30 of them occurred in its spike (S) area.

Appropriate small animal fashions mirroring illness development in people at totally different phases of life are essential to review variations in illness attributable to SARS-CoV-2 VOCs and produce variant-specific vaccines.

About the research 

In the present research, the scientists in contrast the dynamics of SARS-CoV-2 an infection with the Omicron and Delta VOCs in over 15 months outdated and fewer than 5 weeks outdated Mesocricetus auratus (Syrian/golden hamsters). The crew decided the age-related variations within the pathogenicity of SARS-CoV-2 Omicron and Delta infections within the golden hamster mannequin of COVID-19. The research was carried out within the animal biosafety stage 4 (ABSL-4) laboratory on the National Emerging Infectious Diseases Laboratories (NEIDL) of Boston University.

The research consisted of 20 older hamsters aged round 15 to 16 months and 27 youthful hamsters aged 4 to 5 weeks. These two teams have been subdivided into three: controls, Omicron-infected, and Delta-infected animals. Before enrollment, the hamsters have been evaluated by a veterinarian to make sure they have been wholesome. The trial lasted 14 days post-inoculation (DPI), with a subset of hamsters in every subgroup killed at three DPI.

The SARS-CoV-2 Omicron and Delta VOCs procured from the Biodefense and Emerging Infections Research (BEI) Resources have been used to problem the hamsters. The trial endpoints included moribundity (habits, responsiveness, look, respiration) and weight reduction that exceeded humane ranges. Further, blood samples have been collected from the hamsters at 14 DPI.


The outcomes display that Omicron-infected golden hamsters didn’t exhibit weight reduction no matter age. In distinction, Delta an infection resulted in weight lack of practically 7.8% in youthful and round 10% in older hamsters by the seventh day following the SARS-CoV-2 an infection. In addition, a delayed and partial restoration from Delta an infection was noticed within the older teams in comparison with youthful hamsters. 

In the nasal turbinates, tracheas, and lungs, Omicron replicated at comparable ranges to the Delta variant, with no distinct variations within the tissue viral a great deal of aged versus younger animals for both variant at three DPI. SARS-CoV-2 titers have been the bottom in tracheas relative to the lungs in all SARS-CoV-2-infected Syrian hamsters.

The imply half-maximal inhibitory concentrations (IC50) of neutralizing antibodies (NAbs) have been the best in Delta-infected hamsters than the Omicron-infected ones. A big variation in NAbs produced in opposition to the 2 SARS-CoV-2 variants was noticed amongst aged and youthful animals, with excessive ranges in youthful animals.

However, histopathologic variations have been distinguished between the SARS-CoV-2 Omicron and Delta variants within the lungs and nasal passages. The incidence of necrosis was both absent or uncommon in Mesocricetus auratuses with Omicron an infection no matter age, whereas Delta-infected hamsters skilled extreme necrosis acutely within the olfactory epithelium.

While uniformly average acute necrotizing bronchointerstitial pneumonia was reported in Delta-infected Syrian hamsters at three DPI, Omicron an infection brought on gentle pulmonary illness or no distinguished pathology in younger and outdated hamsters.

Most of the acute pathologies noticed within the lungs of hamsters contaminated with Delta on three DPI have been resolved by 14 DPI. Further, the residual findings attributed to compensatory responses ensuing from earlier acute lung illness. However, acute lung pathologies have been absent or seldomly seen in animals inoculated with the SARS-CoV-2 Omicron variant.


The research findings indicate that the SARS-CoV-2 Omicron an infection causes a much less extreme scientific sickness in golden hamsters than the Delta variant-driven an infection, no matter age. However, the Omicron and Delta variants resulted in related viral hundreds within the hamsters. The current findings have been per earlier research illustrating extra evident Delta-associated weight reduction in older hamsters than youthful animals. Likewise, the histologic resolutions 14 DPI with Delta noticed within the current research have been additionally according to prior investigations. 

Together, the research suggests that individuals with Omicron an infection are at excessive danger of by accident infecting others if they don’t abide by the SARS-CoV-2 preventative measures like isolation. This inference was primarily based on comparable viral hundreds noticed in Delta and Omicron an infection, though Omicron had decrease pathogenicity. Moreover, the present findings may support the event of vaccines and different therapeutic approaches for mitigating SARS-CoV-2 VOCs.

*Important discover

bioRxiv publishes preliminary scientific experiences that aren’t peer-reviewed and, due to this fact, shouldn’t be considered conclusive, information scientific observe/health-related habits, or handled as established data.

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