Greetings from day 12 of self-quarantine! Thankfully, I continue to be symptom and fever free and observing the 14-day self-quarantine as a purely protective measure for my family and my community. That being said, it may not be the last time I track my temperature and potential symptoms for 14 days. Nor will I end my current 14-day period with a large party because social distancing still applies even beyond this. Perhaps the decision to refer to the title of a zombie apocalypse movie in this blog seems facetious, but it is truly not.
If you’ve also been inside the last few days to week (and you should have been), you may have been catching up on your Netflix list or starting that home improvement project you’ve been meaning to be. Or you may have seen newscast after newscast emphasizing the importance of the increasing measures to keep people at home and away from large crowds. But one thing I’ve noticed missing is detailed explanations as to why these measures are so important. Which is understandable, considering the limited amount of time we have to turn the tide or flatten the curve.
So the focus of this post is the biology of a pandemic; far from a complete perspective or a comprehensive explanation. However, knowledge is power and being able to understand why your medical professionals are asking, pleading, with you to stay home now more than ever. Also, a big thank you to my classmate and recently matched as future emergency medicine physician in New Jersey, Laura DiTaranti, for reading an early draft and her feedback.
The next 14 days may be the most difficult, most heartbreaking, and yet the most crucial period we have to stop the spread of this virus. Our actions NOW will tell us what our communities will look like 28 days later.
So, first question- why is social distancing so important?
This novel coronavirus has been spreading quickly. The World Health Organization (WHO) announced Monday, March 23 that we have reached over 350,000 cases worldwide. Even more so, the cases have been accelerating exponentially: the first 100,000 cases were confirmed in 67 days, the second 100,000 were confirmed in just 11 days, and the third 100,000 cases were confirmed in only four days. Four days.
When tracking the spread of an infectious disease, epidemiologists- people who study the incidence, distribution, and possible control of diseases- look for the R₀, the R-naught, of a disease. R₀ tells you the average number of people that will catch a disease from one infected and contagious person. For example, the R₀ of measles is 12-18, meaning that for every person infected and contagious with measles, 12-18 more people can catch the disease. Each of those 12-18 people can spread the disease to 12-18 more people. R₀ trees can show how fast a disease spreads. I’ve drawn an example below for measles with an R₀ of 12.
Furthermore, as you may have noticed I wrote in purple in the first example, vaccination rates do not alter R₀. R₀ is a characteristic of the infectious disease, rather than the person it attempts to infect. However, when a contagious, infected person comes into contact with a vaccinated person, the tree’s growth stops in that direction. The example below demonstrates how that looks with measles.
So now we can consider the novel coronavirus COVID-19. Firstly, we cannot determine a definitive R₀ until the pandemic is over. The data at the moment is changing too quickly as the virus continues to spread across the globe. The most recent estimates of R₀ for COVID-19 that I’ve seen are between 1.5 and 3.5. Data from Wuhan suggests an R₀ of 2.2, so I’ll use 2 in my calculations below. With an incubation period of 2-14 days, three generations of spread (6 days-6 weeks) results in the number of infections rising from 2 to 8. With these numbers, there’s two things to keep in mind: 1) the number of infected people can rise every 2 days or 14 days, meaning that the cases can double every other day or every 2 weeks with little ability to predict it and 2) there is no vaccine.
We don’t have the opportunity to cut off any part of the tree’s growth because we don’t have a vaccine. We, as a population, have previously encountered coronaviruses. They’re part of the group of viruses that often cause the common cold. But we’ve never seen this new virus and have never been able to give our immune systems a chance to fight it previously. Which is why we develop vaccines: give your immune system a little taste of a weakened infectious disease and let it prepare its defenses.
Therefore, with COVID-19, the disease may not multiply as fast as measles, but with its wide range of incubation and infectious period and lack of vaccine, it is truly unpredictable and dangerous.
Second question- we’ve been social distancing for days, weeks so why do the numbers keep growing?
For this, look back at the example of the measles R₀ tree. Let’s say that we are currently in the period where we reach the third generation of infected people, when 1,728 people are infected. Because the number of cases has grown quickly and our healthcare system’s capacity to take care of everyone infected is limited, our governments institute social distancing policies in an attempt to limit new infections.
As of today, we’re asked to stay home, avoid large crowds, keep our distance from people so as to not spread the virus via coughs and sneezes. The problem is those 1,728 people have already been going about their days- growing viruses, coughing, sneezing, going to happy hours, eating in restaurants. They may have been without symptoms; they may have been extremely symptomatic and had to work anyway without an ability to take paid sick time; they may be the sole caregiver of a child or elderly person. We won’t see what happens because of those 1,728 people spreading virus until another full incubation period (for example, 7-14 days for measles) later.
The social distancing measures put into place over the past few days will NOT show any results for another 14 days minimum. That’s because even if a person was infected with the virus just one day before following the newly instated stay-at-home protocols, it could take two full weeks to know if that person is infected through showing symptoms. If they chose to not follow those stay-at-home protocols, in that time, they expose every person with whom they come into close contact. Without a vaccine, the ONLY WAY to stop the growth on the R₀ tree is to not interact with anybody. If you consider the purple figures above as people who socially distance, their branch of the tree ends with them and numbers of new infections are small.
So yes, the numbers will continue to go up for some time because the numbers we are seeing now reflect our activity and actions of 2 weeks ago. For example, there is little surprise that Louisiana is currently experiencing a sharp rise in cases just a few weeks after the big crowds at Mardi Gras celebrations. But this rise in numbers does not mean that current and recent social distancing measures are not working. We can only know the success- or failure- of our ability to stop the spread of this virus in a few weeks. When we examine our numbers 28 days later, what will they show then?
Third question- I’m hearing so many different things in the news about who’s affected most, what symptoms we should be looking out for, and whether I can transmit the virus if I don’t have any symptoms. What’s really going on?
The short and simple version of this answer is easy: assume you have the virus at all times regardless of whether you have symptoms or not. It’s that simple. But for more of an explanation, read on…
We are seeing that this virus is having a larger impact on people who are elderly or have pre-existing conditions. As we age or deal with chronic conditions, our immune function decreases. But even healthy people don’t have perfect immune systems. If you’ve seen the TV show Parks and Recreation, even the pillar of aerobic health Chris Traeger comes down with the flu. Even healthy adults get annoying head colds in the winter. So even healthy adults can get a virus that none of us have seen before. We’re betting on the principle that healthy, young people tend to have robust and strong immune systems, but nothing is 100%.
Secondly, the more we see of this virus, the less we seem to know. The cardinal symptoms seem to be cough, fever, shortness of breath, but we’ve also seen loss of taste and smell, muscle aches, gastrointestinal symptoms like diarrhea, vomiting, loss of appetite, general malaise or “blah-ness.” There are also some concerns of co-infections, or having more than one respiratory disease at the same time. In other words, having the flu does not preclude you from having the novel coronavirus.
Finally, can you transmit the virus if you don’t have any symptoms? Based on the last paragraph, which symptoms are you counting as coronavirus? While we’ve been advocating calling your healthcare provider for those big three of cough, fever, and shortness of breath, the variety of symptoms continues to grow as we gain more data. Plus, we all know that one person in our family or circle of friends who gets a cold with barely a sniffle. And we all know that person who gets the same head cold with enough congestion and stuffy nose to knock them out for days.
On film and television, during a zombie apocalypse it’s pretty easy to tell who’s been infected (slack eyed stares, jilted walks, hungry for brains) but what if there was a latency period where someone could be on their way to being a zombie, but not show any of those signs yet. You’d interact with them all the same until they start craving brains, only then realizing you could now be infected too. It may seem a silly example, but it’s literally why we are asking you to stay home. Assume everyone has this virus and the only way, at this moment, to stop your tree branch from growing is to stay home.
We in healthcare cannot do this without you. What is your world going to look like in 28 days?