Facing the dangers of silent spread is necessary to prevent future pandemics

Facing the dangers of silent spread is necessary to prevent future pandemics

By Joshua S. Weitz

The telltale runny nose of a cold, or the fever and aches that accompany the flu, mark the way we classify respiratory illnesses – with their symptoms. Public health messaging is based on these symptoms and urges those who are symptomatic to stay home and avoid others. That makes sense. It reduces the risk of one case becoming many.

But what if the transmission is not necessarily related to symptoms? COVID has shown what diseases can lead to catastrophic social damage when they spread without symptoms. Therefore, preventing future pandemics requires greater investment in targeted public health interventions to reduce transmission – including from infected individuals who are well.

Asymptomatic transmission was essential to COVID’s transition from a rapidly progressing outbreak in Wuhan, China, in early 2020 to a global pandemic that led to more than a million fatalities in the US by May 2022. People who felt good passed on their opinion. infection to others before they develop symptoms (during a presymptomatic phase) or even if they never developed symptoms. Comparisons of early outbreak data showed that about half of the infected persons were asymptomatic. That would be good news if asymptomatic infections were not transmissible. But that wasn’t the case.

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On February 23, 2020, researchers from China, France and the US released a joint analysis of more than 450 COVID transmission events in 93 cities in China. The analysis focused on the serial interval: the time between when someone shows symptoms and when the infected person shows symptoms. Contrary to expectations, the analysis showed that COVID serial intervals were often less than zero, meaning individuals showed symptoms before the person who infected them. These statistics were evidence of rampant presymptomatic transmission. Public health experts tried to raise the alarm that attempts to stop transmission through symptom screening (for example, testing for elevated temperature or shortness of breath) were doomed to failure and that ‘unprecedented measures’ were needed to fight back.

The deadly consequences of asymptomatic transmission soon reached the US. On March 10, 2020, the Skagit Valley Chorale gathered outside Seattle for a rehearsal. Despite attempts to limit physical contact, it became clear within a few days that someone from the group had unknowingly infected others. Ultimately, 53 of the 61 attendees became infected and two died. This super-spreading event revealed that COVID could spread in the air in the absence of symptoms. Yet the relevance of asymptomatic transmission remained contested. On June 8, 2020, declared a top WHO official that asymptomatic transmission was “very rare.” The pandemic raged, but we lost precious time to deal with its silent spread. The consequences were serious. As head of the White House Coronavirus Task Force, Anthony Fauci noted in August 2020: “I’ve never seen a viral disease where you have such a wide range of symptoms, ranging from no symptoms at all, in 40-45 percent of cases, to severe enough to kill you.” Asymptomatic transmission represents a double-edged sword. Individual outcomes may be better, but silent spread leads to many more infections that can lead to worse outcomes for the population.

What can be done to reduce asymptomatic transmission? Initial responses to the pandemic brought restrictions on gatherings and stay-at-home orders. But COVID’s unusual mix of severe and asymptomatic outcomes has prompted a diverse group of stakeholders to invest in unconventional approaches to reduce the risk of silent spread. These approaches include real-time risk assessment, large-scale rapid testing, context-specific masking And improved indoor air quality. Each of these plays a complementary role in reducing silent spread, and if implemented on a large scale, could be essential weapons in the ongoing battle against pandemic-potential pathogens.

In the absence of symptoms, real-time risk assessment driven by outbreak models and distributed via mobile-accessible dashboards could function as a threat forecast. These dashboards can provide mapped information on a variety of infectious disease risks, including: increases in COVID reported in wastewater. People might then decide to avoid events where the risk was beyond their tolerance. But even if someone attends an event, the use of rapid testing and masks on site can limit infections. This could be a huge force for good, especially in… nursing homes and long-term care facilitieswhere a disproportionate share of total COVID fatalities occurred. Regardless of the individual action taken, infrastructure investments in indoor air quality (via improved filtration, air exchange rate and UV-C sterilization in the upper chamber) could improve health outcomes.

Finally, we must commit significant resources to the development and effective distribution of vaccines, both in the US and globally – especially in developing countries. The production of billions of vaccine doses just a year after the emergence of COVID represents an incredible validation of the power of fundamental research and public-private partnerships. However, producing vaccines doesn’t always translate into getting shots in arms. Public health organizations must do that improve reporting to explain why individuals may benefit from vaccines, when to receive vaccines (and boosters), and what each vaccine is for. In the case of COVID, it turned out that mRNA vaccines did reduce the number of symptomatic diseases by more than 90 percent. However, these vaccines do not prevent all infections. This means that vaccinated people can still become infected, test positive and infect others, but their risk of serious consequences is reduced. This is exactly the point. But the fact that vaccines did not provide perfect protection against infections (asymptomatic or otherwise) accelerated development unbridled spread of disinformation that threatens to reduce vaccination rates – not just for flu and COVID, but also for preventable childhood diseases, including measles.

Nearly five years have passed since early warning signs emerged of a novel coronavirus spreading in Wuhan, fueled by asymptomatic transmission that would soon lead to a global pandemic. At the time, the risk to public health and socio-economic stability seemed remote. Since then, scientists, public health experts, government agencies and the biotech sector have developed a range of countermeasures to address the dangers of silent spread – but there is still more to do, including mapping the impact of the silent spread of bird flu in wild and domesticated animals. Translating this momentum into data-driven threat assessments, high-impact interventions (including testing and air quality improvements), faster vaccine deployment, and more effective messaging by clinicians and public health authorities is essential to reducing the ongoing burden of COVID; these actions will better prepare the world to identify, prevent and respond to the threats of future pandemics – before it is too late.

This is an opinion and analysis article, and the views of the author or authors are not necessarily those of Scientific American.