In this Year of the Pandemic is There a Safe Gathering Size?
In this Year of the Pandemic is There a Safe Gathering Size?
By: Mitch Luman, Director of Science Experiences
As the COVID-19 coronavirus first entered our communities, officials knew they had to set limits on large gatherings, all the while scrambling to deduce the definition of “large”. At first, meetings of more than one thousand were discouraged, then it was two hundred fifty, then one hundred and then ten. Eventually, here in Indiana, the state banned all nonessential gatherings entirely.
But what does science say?
Standard thinking relies on the idea that your risk of acquiring COVID-19 increases exponentially with group size. That makes sense. A gathering that is twice as large presents four times a greater chance that you will become infected and a group that is 10 times as large increases the risk 100 times. All this assumes that you’re not doing anything extra to decrease your chances of acquiring the virus like practicing social distancing, or taking other measures to protect yourself and others (which you should be doing).
A new study provides some interesting insights on how large a group can be before the risk of acquiring COVID-19 becomes sufficiently large and the odds are that you will become infected. That study comes from the Journal arXiv and shows mathematically how an epidemic might be controlled without banning gatherings entirely. While any derived number of maximum group size should be taken with a grain of salt, this study provides epidemiologists with new insight of ways of slowing pandemics based on group size and suggests a path forward on how we might return to normal with smaller groups without causing a surge of new cases.
While only a group size of zero can eliminate all risk of acquiring COVID-19, the study teases out what the range of group sizes might be between curbing an epidemic and having it spread like wildfire. For example, let’s say that you permitted gatherings of up to thirty people and you found that your epidemic went out of control. Later, you limited the permitted size of your groups to less than twenty people and found that the epidemic eventually died out. Could there then be a “magic number” between a group that was too large where an epidemic spreads like wildfire and something larger than zero where there was minimal risk of the epidemic spreading? The answer, according to this study, is yes. There is a number, but because it’s kinda squishy, in order to play it safe, officials did early on simply say “no gatherings”. Effective, but no fun. People like to do things together.
23. That’s the number this study said was the threshold for maximum group size. Any more than that and you could expect the virus to rage out of control later. In a group of 23 persons you could still acquire the virus, but it would not spread exponentially. The particular model used in the study relies heavily on a concept known as the friendship paradox, which you might want to check out. It considers how many people in your social network have more friends than you. Keep in mind that this is only a model and no one is saying you should go all out and have a party and invite no more than 23 guests. The actual threshold for COVID-19 is unknown. It’s the concept that is important and that concept says that there is some number in our daily interactions were hanging out with too many people at once is bad for pandemics and smaller groups are better.
We can’t shelter in place forever and we’re not going to have a vaccine for the corona virus until well in the future. Big gatherings with lots of people (think demonstrations, concerts, sporting events) offer larger transmission opportunities for this virus and are a terrible idea for putting the brakes on this pandemic. Washing your hands, wearing face coverings to prevent the spread to others, keeping your social bubbles as small and practicing social distancing are going to be with us for a while. If you’re not going to wear a face mask, at least practice social distancing. If you’re not going to do anything at all, please avoid large groups where people are in close contact. The larger the group, the better your chances of possibly becoming sick, or acquiring the virus and unknowingly transmitting it to someone else.
To read the study Social confinement and mesoscopic localization of epidemics on networks, see the article number 2003.05924 in arxiv.org.
IMAGE CREDIT: NIAID-RML