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

In a latest examine 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
Examine: 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. Picture Credit score: 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 induced 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.

Applicable small animal fashions mirroring illness development in people at completely different phases of life are needed to check variations in illness brought on by SARS-CoV-2 VOCs and produce variant-specific vaccines.

Concerning the examine 

Within the present examine, the scientists in contrast the dynamics of SARS-CoV-2 an infection with the Omicron and Delta VOCs in over 15 months outdated and fewer than 5 weeks outdated Mesocricetus auratus (Syrian/golden hamsters).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 workforce 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 examine was carried out within the animal biosafety degree 4 (ABSL-4) laboratory on the Nationwide Rising Infectious Illnesses Laboratories (NEIDL) of Boston College.

The examine consisted of 20 older hamsters aged round 15 to 16 months and 27 youthful hamsters aged 4 to 5 weeks. These two teams had been subdivided into three: controls, Omicron-infected, and Delta-infected animals. Earlier than enrollment, the hamsters had been evaluated by a veterinarian to make sure they had 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 Rising Infections Analysis (BEI) Assets had been used to problem the hamsters. The trial endpoints included moribundity (conduct, responsiveness, look, respiration) and weight reduction that exceeded humane ranges. Additional, blood samples had been collected from the hamsters at 14 DPI.


The outcomes reveal 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. As well as, a delayed and partial restoration from Delta an infection was noticed within the older teams in comparison with youthful hamsters. 

Within 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 had 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) had been the very best in Delta-infected hamsters than the Omicron-infected ones. A big variation in NAbs produced towards the 2 SARS-CoV-2 variants was noticed amongst aged and youthful animals, with excessive ranges in youthful animals.

Nonetheless, histopathologic variations had been outstanding 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.

Whereas uniformly reasonable acute necrotizing bronchointerstitial pneumonia was reported in Delta-infected Syrian hamsters at three DPI, Omicron an infection induced delicate pulmonary illness or no outstanding pathology in younger and outdated hamsters.

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


The examine 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. Nonetheless, the Omicron and Delta variants resulted in comparable viral masses within the hamsters. The current findings had been according to 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 examine had been additionally in step with prior investigations. 

Collectively, the examine suggests that folks with Omicron an infection are at excessive threat of by chance infecting others if they don’t abide by the SARS-CoV-2 preventative measures like isolation. This inference was primarily based on comparable viral masses noticed in Delta and Omicron an infection, though Omicron had decrease pathogenicity. Furthermore, the present findings may help the event of vaccines and different therapeutic approaches for mitigating SARS-CoV-2 VOCs.

*Vital discover

bioRxiv publishes preliminary scientific stories that aren’t peer-reviewed and, due to this fact, shouldn’t be thought to be conclusive, information scientific apply/health-related conduct, or handled as established data.

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