2023-08-08 11:15:06
Mathematical models have helped to understand the dynamics of epidemics, especially in the evolution of the recent SARS-CoV-2 coronavirus pandemic. These models explain the phenomenon of herd immunity: when enough people are immune to a virus (either after overcoming an infection or after receiving a vaccine), the probability that the pathogen will find new hosts approaches zero. In this way, even unvaccinated people are protected.
Scientists have found a mathematical equivalence between models of sterilizing immunity (when the virus cannot reinfect, even mildly) and attenuating immunity (which does not block infection, but only makes it less likely or softens the symptoms) in epidemics . According to the scientists, these mathematical equivalences reveal that attenuating immunity, easier to achieve, is “a valuable weapon to achieve herd immunity.”
The study is the work of Iker Atienza-Diez and Luís F. Seoane, both from the National Center for Biotechnology (CNB), dependent on the Higher Council for Scientific Research (CSIC) in Spain.
“Classical models suggest that, to achieve this group protection, individual immunity must be sterilizing. However, the new mathematical model alters these forecasts, clearly indicating how attenuating immunity can achieve the same effect as sterilizing immunity,” says Seoane.
The results obtained consider cross-immunity, that is, protection from past infections against future pathogens, even when dealing with different strains, and in the very long term, when successive infections by increasingly distant strains accumulate in a population. This has happened with SARS-CoV-2 during the pandemic and with the influenza virus over the last few decades.
Herd immunity is achieved when enough people are immune to a virus, after overcoming an infection or receiving a vaccine. In the image, a vaccine. (Photo: Jim Gathany/CDC)
The new models suggest that the immunological memory effect alters the properties that each new outbreak can have. This effect also causes a qualitative difference to appear spontaneously between frequent processes with a low incidence and others that are very rare but capable of affecting the entire population. In other words, as Atienza-Diez points out, “the mathematical modeling of cross-immunity suggests the emergence of processes similar to epidemics together with others more similar to pandemics. This natural separation of scales did not occur in models that did not consider immunological memory.
The study is titled “Long- and short-term effects of cross-immunity in epidemic dynamics”. And it has been published in the academic journal Chaos, Solitons & Fractals. (Source: CSIC)
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