As vaccination rates rise, more and more governments are loosening the measures they had taken to curb Covid-19 transmission. But that could encourage the spread of virus mutations that are resistant to the vaccine, researchers warn based on a new modeling study. According to this, a quick and consistent vaccination of the world population lowers the risk of resistant strains. However, if there is a renewed increase in transmissions in a phase in which many people have already been vaccinated – because measures such as keeping your distance and wearing a mask were reduced too quickly – a vaccine-resistant mutation could spread.
Vaccinations against the Sars-CoV-2 coronavirus raise hopes in many people that they will soon be able to leave the pandemic and the associated restrictions behind. Since high-risk groups such as the elderly and the chronically ill are already largely protected in many countries and less severe cases and deaths are to be expected, numerous governments are already loosening measures such as contact restrictions and the obligation to wear a mask. But that could be dangerous, warns a research team led by Simon Rella from the Institute of Science and Technology (IST) Austria.
Spread of resistant strains modeled
“Using a statistical model, we examined how the vaccination rate and non-pharmaceutical measures affect the likelihood of a resistant strain occurring,” the researchers explain. “We used parameters that are realistically similar to Sars-CoV transmission.” In their model, they assumed that a virus like Sars-CoV-2 spreads over three years in a population of ten million people, with after the first vaccinations start after a year. They varied how fast the vaccination rate progresses and how much the transmission is limited by additional measures such as contact restrictions, distance requirements and mask requirements.
The result: “As expected, we found that a high vaccination rate lowers the likelihood of a resistant strain occurring,” report Rella and his colleagues. “A counterintuitive result of our analysis is that the highest risk of the establishment of resistant strains is when a large part of the population has already been vaccinated, but transmission is not controlled.” In this case, the high transmission rate would ensure the survival of the mutated virus strain , while the high number of people vaccinated at the same time means a selection advantage over the wild type. “The establishment of a resistant strain at this point in time can lead to several rounds of the evolution of resistant strains, with vaccine development having to catch up in the evolutionary arms race against novel strains,” warn the researchers.
Keep your distance despite vaccination
“Our results suggest that policymakers and individuals should consider maintaining non-pharmaceutical interventions and transmission-reducing behaviors throughout the vaccination period,” explain Rella and his team. If the transmission of the virus is kept low during the vaccination campaigns through measures such as distance requirements, resistant strains could arise, but spread only little, so that they do not gain much influence and disappear again on their own.
“Additional factors that can make these interventions even more effective are increased and widespread testing, rigorous contact tracing, high sequencing rates for positive cases, and travel restrictions,” the researchers said. They did not model the individual effects of these factors. In principle, however, close monitoring of newly emerging variants and suitable countermeasures are important in order to prevent strains against which the current vaccines are ineffective from spreading.
Global cooperation is important
According to the researchers, global cooperation plays a major role in this: “Without global coordination, resistant vaccine strains could be eliminated in some populations, but persist in others,” they warn. Nick Davies of the London School of Hygiene and Tropical Medicine, who was not involved in the study, also affirmed: “Every country should do its part to avoid the creation of fertile soil for viral evolution as much as possible – a goal which fortunately is broadly in line with public health and economic goals. Ultimately, however, dealing with the emergence of a vaccine resistant strain is a global problem, not a national one; as soon as a vaccine escape mutant appears anywhere, it becomes everyone’s problem. “
Source: Simon Rella (Institute of Science and Technology (IST) Austria) et al., Scientific Reports, doi: 10.1038 / s41598-021-95025-3