Author: Dr. Francis Collins
NIH Directo’s Blog
With the start of summer coming soon, many are hopeful that the warmer weather will slow the spread of SARS-CoV-2, the novel coronavirus that causes COVID-19. There have been hints from lab experiments that increased temperature and humidity may reduce the viability of SARS-CoV-2. Meanwhile, other coronaviruses that cause less severe diseases, such as the common cold, do spread more slowly among people during the summer.
We’ll obviously have to wait a few months to get the data. But for now, many researchers have their doubts that the COVID-19 pandemic will enter a needed summertime lull. Among them are some experts on infectious disease transmission and climate modeling, who ran a series of sophisticated computer simulations of how the virus will likely spread over the coming months . This research team found that humans’ current lack of immunity to SARS-CoV-2—not the weather—will likely be a primary factor driving the continued, rapid spread of the novel coronavirus this summer and into the fall.
These sobering predictions, published recently in the journal Science, come from studies led by Rachel Baker and Bryan Grenfell at Princeton Environmental Institute, Princeton, NJ. The Grenfell lab has long studied the dynamics of infectious illnesses, including seasonal influenza and respiratory syncytial virus (RSV). Last year, they published one of the first studies to look at how our warming climate might influence those dynamics in the coming years .
Those earlier studies focused on well-known human infectious diseases. Less clear is how seasonal variations in the weather might modulate the spread of a new virus that the vast majority of people and their immune systems have yet to encounter.
In the new study, the researchers developed a mathematical model to simulate how seasonal changes in temperature might influence the trajectory of COVID-19 in cities around the world. Of course, because the virus emerged on the scene only recently, we don’t know very much about how it will respond to warming conditions. So, the researchers ran three different scenarios based on what’s known about the role of climate in the spread of other viruses, including two coronaviruses, called OC43 and HKU1, that are known to cause common colds in people.
In all three scenarios, their models showed that climate only would become an important seasonal factor in controlling COVID-19 once a large proportion of people within a given community are immune or resistant to infection. In fact, the team found that, even if one assumes that SARS-CoV-2 is as sensitive to climate as other seasonal viruses, summer heat still would not be enough of a mitigator right now to slow its initial, rapid spread through the human population. That’s also clear from the rapid spread of COVID-19 that’s currently occurring in Brazil, Ecuador, and some other tropical nations.
Over the longer term, as more people develop immunity, the researchers suggest that COVID-19 may likely fall into a seasonal pattern similar to those seen with diseases caused by other coronaviruses. Long before then, NIH is working intensively with partners from all sectors to make sure that safe, effective treatments and vaccines will be available to help prevent the tragic, heavy loss of life that we’re seeing now.
Of course, climate is just one key factor to consider in evaluating the course of this disease. And, there is a glimmer of hope in one of the group’s models. The researchers incorporated the effects of control measures, such as physical distancing, with climate. It appears from this model that such measures, in combination with warm temperatures, actually might combine well to help slow the spread of this devastating virus. It’s a reminder that physical distancing will remain our best weapon into the summer to slow or prevent the spread of COVID-19. So, keep wearing those masks and staying 6 feet or more apart!
References: Susceptible supply limits the role of climate in the early SARS-CoV-2 pandemic. Baker RE, Yang W, Vecchi GA, Metcalf CJE, Grenfell BT. Science. 2020 May 18. [Online ahead of print.]  Epidemic dynamics of respiratory syncytial virus in current and future climates. Baker RE, Mahmud AS, Wagner CE, Yang W, Pitzer VE, Viboud C, Vecchi GA, Metcalf CJE, Grenfell BT.Nat Commun. 2019 Dec 4;10(1):5512.