SARS-CoV-2 transmission, vaccination rate and the fate of resistant strains

Abstract

Vaccines are thought to be the best available solution for controlling the ongoing SARS-CoV-2 pandemic [1,2]. However, the emergence of vaccine-resistant strains [3-6] may come too rapidly for current vaccine developments to alleviate the health, economic and social consequences of the pandemic [7,8]. To quantify and characterize the risk of such a scenario, we created a SIR-derived model [9,10] with initial stochastic dynamics of the vaccine-resistant strain to study the probability of its emergence and establishment. Using parameters realistically resembling SARS-CoV-2 transmission, we model a wave-like pattern of the pandemic and consider the impact of the rate of vaccination and the strength of non-pharmaceutical intervention measures on the probability of emergence of a resistant strain. We found a counterintuitive result that the highest probability for the establishment of the resistant strain comes at a time of reduced non-pharmaceutical intervention measures when most individuals of the population have been vaccinated. Consequently, we show that a period of transmission reduction close to the end of the vaccination campaign can substantially reduce the probability of resistant strain establishment. Our results suggest that policymakers and individuals should consider maintaining non-pharmaceutical interventions [7,11,12] throughout the entire vaccination period.

Substantial impact of post-vaccination contacts on cumulative infections during viral epidemics

“…The selective environment within such a partially susceptible host in the days immediately following the administration of a perfect vaccine is not completely equivalent to that within a host that remains partially susceptible in the months following the administration of an imperfect vaccine. Nonetheless, we believe that this and related work 36 , 37 unequivocally demonstrates the continued importance of reducing host-host contact well after the onset of mass vaccination.…”

Vaccine escape in a heterogeneous population: insights for SARS-CoV-2 from a simple model

“…to what extent would variants abrogate the different vaccine effects of susceptibility, infectivity and disease reduction. An extreme approach, where vaccination is perfect against wild-type but completely ineffective against an escape variant, found that establishment of the resistant strain was most likely when most of the population had been vaccinated [ 38 ].…”

Vaccination strategies when vaccines are scarce: On conflicts between reducing the burden and avoiding the evolution of escape mutants

“…We only consider the emergence of vaccine escape mutants but do not track their spread. As already mentioned in the model section, the fate of these mutants is subject to stochasticity as long as they are rare (Rella et al,2021). Especially when the distribution of secondary cases is overdispersed – i.e.…”

“…This includes in particular the extent at which social distancing restrictions are lifted already during a vaccination campaign. This affects the establishment of escape variants (Rella et al,2021), but also their propagation once frequent. A further factor that is crucial for the fate of escape mutants, short-term and long-term, is the degree up to which vaccination is still effective against them.…”