The COVID-19 pandemic has shown that locking down a country is relatively simple, but exiting is far more complicated. The pace and order of easing restrictions can create dissatisfaction among impatient people and insecurity among vulnerable groups. Now, based on mathematical modelling, researchers have developed a model for how to exit COVID-19 lockdown while limiting the risk of new waves of infection. They think that the key to reopening in the future will be to protect the vulnerable population and their closest contacts.
Most people who have experienced COVID lockdown are familiar with this discussion. Lockdowns cause huge societal, psychological and economic harm. The lack of knowledge about the pandemic and experience in reopening have given frustration and emotions free rein among both the population and decision-makers. A group of mathematicians with expertise in modelling has therefore tried to qualify the debate by entering many facts into their model to arrive at a proposal on the key risk factors in reopening society.
“Our study shows that the most important factors to consider are the transmission of infection at the time of reopening, population immunity and the proportion of vulnerable people in the population. The right combination of factors enables society to open up completely if, and only if, vulnerable groups are protected without isolating them and the planned measures for protecting them are actually implemented,” explains Bram van Bunnik, Postdoctoral Fellow at the Epidemiology Research Group, Usher Institute, University of Edinburgh, United Kingdom.
Still not fully understood
The researchers behind the study, like many other research groups, were doing something completely different when the COVID-19 pandemic broke out in spring 2020: mathematical modelling of the spread of antibiotic resistance, another global health challenge. However, after most countries were about to reopen after a few months of lockdown, the researchers clearly realized that their expertise could help in the pandemic.
“Several mathematical modelling studies had investigated how the various physical restrictions affected the actual and predicted trajectory of the COVID-19 pandemic, but very few had considered shielding certain population members, even though this was actually part of the national strategy to limit the negative effects of COVID-19. We therefore decided to determine the effect of shielding especially vulnerable groups,” says Bram van Bunnik.
The researchers therefore developed an advanced mathematical model based on various key data such as the duration of lockdown and more rapid or slow transition to reopening and, most importantly, the balance between increasing the protection of the vulnerable segment of the population while easing restrictions for the general population.
“Our goal was to investigate the extent to which society could reopen again if the most vulnerable members of the population were protected. Although the risk factors for severe COVID-19 disease are still not fully understood, the United Kingdom government identified 1.5 million potentially vulnerable individuals based on the key risk factors defined by WHO: those older than 60 years and those with underlying conditions, such as cardiovascular disease, hypertension, diabetes. chronic respiratory disease and cancer,” explains Bram van Bunnik.
Protect – not isolate
The mathematical model identified key parameters that were absolutely crucial to whether society could reopen without starting a new wave of COVID-19. Unsurprisingly, the decisive factors were the actual number of people infected and especially the infection pressure, which shows whether an epidemic is growing, stagnating or shrinking. Sufficiently low numbers are a basic precondition for justifying reopening.
“Another crucial factor is the proportion of the population that is vulnerable to serious illness and death. Our model is based on being able to protect them by creating a shield around them of people in nursing homes, hospitals and in their homes who can support them and ensure that they have good quality of life and yet are protected from infection,” says Bram van Bunnik.
The researchers call their model the segmenting and shielding exit strategy, and their calculations show that this could enable earlier reopening after pandemics such as COVID-19. Further, the strategy could be greatly strengthened by infrastructure and technological support for effective biosecurity at both the institutional (such as care homes and hospitals) and household levels to keep transmission rates low between and within shielders and the vulnerable population.
“This will require training, high standards of hygiene, personal protective equipment and screening everyone in contact with the vulnerable population. Then, how the segmenting and shielding strategy is communicated and implemented is incredibly important. Having the vulnerable population feel that they are protected rather than isolated is absolutely crucial because, as we have seen during the pandemic, isolation can have enormous psychological effects and significantly reduce the quality of life,” explains Bram van Bunnik.
Important input for the future
According to the researchers, a major uncertainty factor in the mathematical model is the degree to which immunity develops in the population. When the study was conducted in connection with the first wave of the pandemic, the researchers had little idea of how long people who had COVID-19 would remain immune and no idea when vaccination could be initiated. The model was therefore based om very cautious estimates.
“We have assumed in the model that only short-term immunity was developed, and as long as this is longer than three months, the model should apply. We were concerned that there was no acquired immunity to COVID-19, because then the epidemic would become considerably more difficult to control. With vaccination, the model provides a far more optimistic scenario,” says Bram van Bunnik.
The researchers’ models and calculations have been continually submitted to the United Kingdom government throughout the pandemic but have only been used to a certain extent; one reason is that the segmentation mindset can be very easily misinterpreted. Nevertheless, the researchers think that the new results may prove extremely significant in the future.
“This segmentation and shielding strategy could potentially be used for any infectious disease as soon as we know which segments of the population cannot be treated or are at risk of serious illness from the disease. Whether future decision-makers and populations will find the segmentation strategy acceptable or not, our calculation models provide important input for the future on the importance of contact between population segments and the relationship between physical distancing and the transmission of infection,” concludes Bram van Bunnik.