Implications for SARS-CoV-2 Immunological Evasion

In a recent study posted on medrex sib* Researchers used a preprint server to model the implications of immunological avoidance for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Background

The ability of SARS-CoV-2 to evade human immunity using mutations that weaken antibody binding is a key factor in the highly unpredictable viral infection. To understand and respond to this uncertain period of the COVID-19 pandemic, it is important to understand the tendency of emerging SARS-CoV-2 strains to cause waves of infection, continue to circulate, and co-circulate with established strains. Knowledge is essential.

Immune evasion affects short- and long-term viral infection levels, potential changes in disease severity, and efficacy of vaccines and treatments, especially monoclonal antibodies. The ability to predict trends in viral mutation is of immense value in the development of non-pharmaceutical and biologic therapies.

About research

In the present study, researchers employed an epidemiological modeling framework to provide a quantitative interpretation of the impact of immune evasion on competition and selection dynamics among SARS-CoV-2 strains in an epidemic setting.

The team built a Susceptibility-Infectivity-Recovery-Susceptibility (SIRS) model to assess long-term and short-term transmission of emerging SARS-CoV-2 strains. The model consists of her two parallel sets of compartments representing individuals infected with the original strain and the invading strain. This model considered disease transmission, immunity reduction, and immunity induction by exposure to either or both strains.

To simulate symmetrical antigenic drift, the team set up cross-immunity of native strains in response to invading strains (C_overview) and the native strain (C_IVO) equal. In short-duration scenarios, full cross-immunity was assumed to exist between the two strains. Therefore, it is not possible to have immunity against two strains at the same time.

The initial environment of the model was established such that the original strain was in its own steady state and the fraction of active infection remained constant. To check the steady-state distribution of individuals within each compartment, he ran simulations for 10,000 days without an invading strain. The team utilized this model to assess the short-term ability of invasive strains to induce transmission waves and the long-term impact of invasive strains on transmission propensity. In the short term, an outbreak was considered successful if the infected individual exceeded the original value within her first 180 days.

result

Although viral invasion may have a small impact on the transmission of natural virus strains in a short period of time, the impact of invading strains can spread rapidly. This leads to a marked increase in general short-term viral infection essential for successful entry compared to failed entry and constitutes the baseline infection noted in the original strain. The higher transmissibility observed in the invasive strains, together with mutual immunological avoidance, leads to the propagation of larger transmissive waves. The team noted that in the presence of symmetrically low cross-immunity, long-term infection was highest, resulting in co-circulation of virus strains. As cross-immunity levels decrease, so does strain competition.

Inheritance is rare when immune evasion is perfectly symmetric, whereas unilateral immune evasion is particularly associated with the intrinsic reproductive number (R₀) is any natural strain R or greater.₀However, the exposure required for successful invasion is similar to that of the reciprocal symmetrical immune evasion situation regarding extinction and co-circulation of the original strain.

Following the emergence of invasive strains, short-term trends in infection in asymmetric situations are comparable to those observed in symmetric situations. Furthermore, the nature of immunity associated with the invasive strain he distinguishes between the two scenarios. In the long term, the immunity generated by the invading strain inhibits the native strain’s ability to spread, resulting in its extinction. This leads to reduced transmission of preexisting strains with limited advantages over invasive strains, unless the invasive strain exhibits a weaker dominant position. Moreover, the strong cross-immunity induced by strains invading in response to pre-existing strains did not significantly affect global and long-term transmission of infectious diseases.

Conclusion

The results of this study indicate that viral evolution is a key factor in determining infection rates at this stage of the COVID-19 pandemic. This is because intrusion events can increase future widespread infections. This study highlighted the importance of early data describing immune responses to antibody evasion and variant development in the development of SARS-CoV-2 vaccines and other mitigation strategies. Researchers also believe the findings indicate that the emergence of SARS-CoV-2 serotypes is a potential extra risk associated with current public health policies.

*Important Notices

medRxiv publishes non-peer-reviewed, preliminary scientific reports and should not be considered conclusive, to guide clinical practice/health-related actions, or to be treated as established information .