Spread of Coronavirus Strains Spurred by Super-Spreading Events

The superspreader events that first sowed the coronavirus in the United States are keeping the pandemic on fire, with experts pointing to human behavior and social circles as the main drivers.

The problem persists even as the country nears the milestone of having half of its population fully immunized. In a religious camp in South Texas at the end of June, an epidemic was linked to more than 125 cases of Covid-19. Eighty-five infections in central Illinois were attributed to a summer camp in mid-June.

Similar examples have emerged internationally: a June 26 disco party in the Netherlands was subsequently linked to 160 new cases, and the Miss Mexico pageant in Chihuahua town was halted in early July after nearly half of the candidates tested positive.

Throughout the pandemic, superpropagators – infected individuals who spread the virus disproportionately to many others – have fueled clusters of infection that often make the virus difficult to contain. In other words, when the coronavirus infiltrates communities, super-spraying events are the defining moments when the pathogen takes siege.

Now, with the more contagious delta variant of the virus circulating in the United States and around the world, experts warn that without adequate mitigation measures, super-spread events are a major threat to vulnerable communities and risk putting people at risk. hard-earned gains to lower the number of cases.

But even as the pandemic evolves and new variants emerge that are more transmissible or may cause more severe disease, human behavior remains one of the most important parts of the equation.

“It’s not just about the variants. It’s also about how people interact,” said David Dowdy, associate professor of infectious disease epidemiology at the Johns Hopkins Bloomberg School of Public Health. “Right now people definitely distance themselves less, mask themselves less, go to larger gatherings, and meanwhile immunization rates are not rising so fast.”

All of these things combined can create a perfect storm, increasing the chances of new transmissions getting out of hand.

Overall, the vaccines have helped provide a wall of defense against large epidemics, but with the highly transmissible delta variant spreading rapidly across the country, areas with lagging vaccination rates are at significant risk.

“There are networks of people who interact closely with people and are not widely vaccinated and who remain at risk for major epidemics,” said Dowdy. “This will be true regardless of which variant you’re talking about. “

One way to avoid big spikes in delta variant infections is to minimize the likelihood of super-spreading events occurring, said Joshua Batson, chief data scientist at The Public Health Company, a California startup that uses technology to monitor and contain infectious disease outbreaks. This involves doubling up on vaccination efforts and may require the reimposition of certain restrictions, such as social distancing and mask-wearing rules, in areas where outbreaks occur.

“Mathematically, if you remove the super spread events, we don’t have a pandemic,” Batson said. “If you just focus on those scenarios where the really bad things are happening, you will have a disease that will kind of spit out.”

Since the early days of the pandemic, super-spreaders have played a disproportionate role in the transmission of the virus. In Wuhan, China, where Covid-19 was first identified, a cluster of infections at a seafood market in December 2019 was seen as the first example of a super-spreading event. In the United States, a Biogen corporate meeting in Boston in February 2020 was then linked to 20,000 cases of Covid-19, helping the virus take hold in the region.

These events are of concern because they often provide the spark for a subsequent hell. Once they happen, communities can be quickly overwhelmed.

“It’s one unlucky thing, then another unlucky thing and then you get these explosions,” Batson said. “You go from almost no Covid in one area to a lot of cases.”

If the virus spreads unhindered, there is also the risk that new, more disturbing variants will emerge, he added.

Research is ongoing, but it is not yet fully understood why some people become super broadcaster while others do not. A study published last year by scientists at the London School of Hygiene and Tropical Medicine found that around 10% of people infected with Covid-19 could be responsible for around 80% of the spread of the virus.

While human behavior can lead to new epidemics and their severity, changes in behavior can also prevent the worst outcomes.

There are three main forces that fuel the transmission of Covid-19. The first is the virus’s own biology, which determines how contagious it is and how easily it could spread. The second force is the susceptibility of the exposed population to the virus. The third factor is the behavior of this population, that is, the way they interact and provide possibilities for the spread of a virus.

“Compared to last year, these three forces have changed dramatically,” said Max Lau, assistant professor at the Rollins School of Public Health at Emory University.

While vaccines have made many people in the United States less susceptible to the virus, the delta variant is more transmissible, and many restrictions that were in place to slow transmission during the height of the pandemic have since been lifted.

“These three forces are dynamically changing and counterbalancing each other,” Lau said.

Behavior changes can alter the balance, helping to protect populations even in the face of new variants. In other words, if immunization improves overall and people remain vigilant, the country could avoid a summer wave.

“Our company is not where it was last spring or last winter,” Batson said. “A lot of people have been vaccinated, a lot of people have had Covid and a lot of people are taking the right precautions. If you put these things together, it means if Covid has gotten stronger, so have we.”