In influencing the trajectory of the pandemic stage of an emerging pathogen, a population’s susceptibility to a novel disease is more influential than climate factors like humidity. The results – based on a model informed by climate-dependence of known coronaviruses – may inform researchers’ effort to understand the likely trajectory of the ongoing COVID-19 pandemic, including as summer and its associated temperature and humidity changes, hoped for to bring respite from the pandemic, set in in parts of the world. Preliminary evidence suggests that climate factors like humidity may impact the transmission of SARS-CoV-2. Yet, whether these factors could substantially alter the pandemic trajectory over the remainder of 2020 remains a question, given that a population’s high susceptibility (or low immunity) to the virus is also a core influence. To better understand this, Rachel Baker and colleagues used a climate-driven epidemiological model fitted with U.S. data on four other circulating and seasonal coronaviruses. In simulations of their model in different cities in high latitudes and tropical locations, they found that even in tropical cities, with conditions that should hinder virus transmission, outbreak growth remained significant. Following their analyses, the authors report that while climate effects may drive modest changes to the peak size and duration of the pandemic, summer weather will not likely limit pandemic growth, as the pandemic trajectory is modulated more by population susceptibility to the illness. In a further, preliminary analysis of how non-pharmaceutical control measures (including shelter-at-home orders) influence spread of SARS-CoV-2, the authors report these measures may moderate the pandemic-climate interaction to some extent, by removing susceptible people from the population. The results suggest that population susceptibility remains the driving factor in SARS-CoV-2 spread over summer and suggest that, unless effective control measures are maintained, significant numbers of COVID-19 cases in the coming months are likely even in more humid and warmer climates.
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