Call to cut Covid transmission during jab campaigns to stop resistant strains

Reducing coronavirus transmission through measures such as face masks during vaccination programmes is necessary to lower the likelihood of vaccine-resistant strains emerging, a study has suggested.

Researchers simulated the probability that a vaccine-resistant strain may emerge in a population of 10 million people over three years with vaccinations starting after the first year.

The modelling suggested a fast rate of vaccination decreases the probability of a resistant strain.

However, it also showed that if relaxation of non-pharmaceutical interventions happened when most people in the population had already been vaccinated, the probability of a resistant strain emerging greatly increased.

Fyodor Kondrashov, of the Institute of Science and Technology Austria, and colleagues suggest this may be due to a growth advantage of the resistant strain over the original strain in the presence of vaccines.

The study also found that in scenarios when the resistant strain became established, it initially emerged around the time when 60% of the population had been vaccinated.

Researchers recommended targeted non-pharmaceutical measures, such as mask wearing, extensive testing and social distancing, to reduce virus transmission rates towards the end of vaccination campaigns and allow emergent resistant strains to naturally become extinct.

They said any measures that reduce transmission, such as increased and widespread testing, rigorous contact tracing, high rates of sequencing and travel restrictions could increase the probability of emergent virus extinction.

However, the study did not model the effect of these individual measures on virus transmission.

Prof Kondrashov said: “Of course we all hope for the best, that vaccine resistance perhaps does not evolve in the course of this pandemic.

“But we also urge caution that evolution is a very powerful force and that maintaining some reasonable precautions throughout the whole vaccination period may actually be a good tool to control this evolution.”

The study is published in Scientific Reports.