Do pathogens always evolve to be less virulent? The virulence–transmission trade-off in light of the COVID-19 pandemic

Abstract

The direction the evolution of virulence takes in connection with any pathogen is a long-standing question. Formerly, it was theorized that pathogens should always evolve to be less virulent. As observations were not in line with this theoretical outcome, new theories emerged, chief among them the transmission–virulence trade-off hypotheses, which predicts an intermediate level of virulence as the endpoint of evolution. At the moment, we are very much interested in the future evolution of COVID-19’s virulence. Here, we show that the disease does not fulfill all the assumptions of the hypothesis. In the case of COVID-19, a higher viral load does not mean a higher risk of death; immunity is not long-lasting; other hosts can act as reservoirs for the virus; and death as a consequence of viral infection does not shorten the infectious period. Consequently, we cannot predict the short- or long-term evolution of the virulence of COVID-19.

Epidemiological dominance of the most virulent HPAIV H5N1 clade 2.3.4.4b strains: insights from experimental infections of Pekin ducks (Anas platyrynchos)

“…Alternatively, the "transmission-virulence trade-off" model seems more accurate in describing the epidemiological situation of HPAIV, i.e. virulence and transmission can be positively correlated at least as long as transmission of a certain viral lineage to other hosts is advantageous compared to other lineages and not limited by the number of susceptible individuals in the given host populations 43,44 , i.e. here the huge multispecies metapopulations of wild aquatic birds and poultry.…”

Do disease-modifying antirheumatic drugs and non-steroidal anti-inflammatory drugs increase the burden on ankylosing spondylitis patients with mild-moderate COVID-19? evidence from a retrospective cohort study

“…Over the past 4 years, new variants of the virus have emerged, which exhibit increased transmissibility but fortunately, have been found to be less virulent than the original virus ( Nyberg et al, 2022 ). For the majority of patients, COVID-19 presents as a mild or moderate disease, with 70%–80% of those infected experiencing mild flu-like symptoms and not requiring hospitalization, even during the early stages of the pandemic ( Kun et al, 2023 ). Previous research has predominantly focused on severe outcomes of COVID-19 in patients with AS, such as hospitalization, admission to intensive care units, mechanical ventilation, and death.…”

COVID-19 Outcomes in Kidney Transplant Recipients in a German Transplant Center

“…The World Health Organization (WHO) proclaimed the Coronavirus disease 2019 (COVID-19) as a global pandemic in March 2020 [ 1 ]. The rapid emergence and subsequent dominance of new variants on a global scale have become characteristic features of SARS-CoV-2 [ 2 ]. The Omicron variant and the time period of its global dominance over other lineages, which can be defined as the Omicron era, relative to previous variants, was characterized by a less severe disease course, lower risk of hospitalization, ICU admission and death [ 3 , 4 ].…”