[I found the below text among comments on this page. There is no direct link to the comment itself. There are many supporting sources and the information sounds right. Additionally, no harm will come from upping indoor humidity. ABN]
Extremely important right now: Humidity is a major protectant from COVID-19. Both by reducing infection and reducing severity of symptoms.
I am a researcher who just wrote a paper on the subject. Please help me get the word out. This is not hype. Read all the papers on the subject.
If there is a pandemic in America, it could be Trump’s Waterloo.
Defending Against COVID-19 Through Indoor Humidification
Daniel A. Hess
Virology Researcher, Rockville, MD
February 26, 2020
There is ample research showing that viral outbreaks similar to COVID-19 are strongly correlated with humidity levels. Cold and flu generally peak during the winter months in temperate zones, when indoor humidity is low. Notably, influenza and cold viruses tend to survive far longer in the air when the ambient humidity is low than when the ambient humidity is high. Further, there is strong evidence that the severity of respiratory infection is similarly humidity dependent, as lower humidity leads to more severe flu illness and greater likelihood of death. Influenza and COVID-19 are very similar in that death typically results from pneumonia that leads to acute respiratory failure.
Thus, indoor humidification, particularly to 50% relative humidity or higher, is seen as a strong partial defense against COVID-19, by two different mechanisms. First, by reducing the amount of time that virus particles remain infectious in the air, humidification is expected to substantially reduce R0, the reproductive number that represents outbreak contagiousness. Second, by reducing severity of respiratory infection, mortality rates from COVID-19, currently estimated at 2.3%, may be substantially reduced.
Indoor humidification is readily available almost everywhere and can be achieved by common humidifiers and even by boiling water in impoverished areas where humidifiers are not available. Available research strongly suggests that humidification in homes, hospitals, schools and other public areas will dramatically reduce both COVID-19 transmission and COVID-19 mortality among those who become infected. Even in areas where medical infrastructure becomes overwhelmed during pandemic conditions, indoor humidification will remain widely available as a defense against COVID-19 infection and severity.
Evidence so far is strong that COVID-19 exhibits climate and seasonal characteristics similar to influenzas and the common cold. By mimicking the environmental conditions of the summer months through indoor humidification, it is believed that COVID-19 incidence and severity will be sharply reduced.
Indoor humidification, especially to 50% relative humidity or higher, is likely to emerge as a robust tool that will be widely adopted as a defense against COVID-19.
I. Virus particles remain active longer in dry air than in humid air: citations
1. Noti et al. (2013) High Humidity Leads to Loss of Infectious Influenza Virus from Simulated Coughs. PLoS One. 2013; 8(2): e57485.
2. Tamerius JD, et al. (2013) Environmental predictors of seasonal influenza epidemics across temperate and tropical climates. PLoS Pathog 9:e1003194, and erratum 2013 Nov;9(11).
3. Shaman J, Pitzer VE, Viboud C, Grenfell BT, Lipsitch M (2010) Absolute humidity and the seasonal onset of influenza in the continental United States. PLoS Biol 8(2): e1000316.
4. Shaman J, Goldstein E, Lipsitch M (2011) Absolute humidity and pandemic versus epidemic influenza. Am J Epidemiol 173: 127–135
5. Lowen AC, Mubareka S, Steel J, Palese P (2007) Influenza virus transmission is dependent on relative humidity and temperature. PLoS Pathog 3(10): 1470–1476.
6. Schaffer FL, Soergel ME, Straube DC (1976) Survival of airborne influenza virus: effects of propagating host, relative humidity, and composition of spray fluids, Arch Virol. 51: 263–273.
7. Hanley BP, Borup B (2010) Aerosol influenza transmission risk contours: A study of humid tropics versus winter temperate zone. Virol J 7: 98.
8. Yang W, Marr LC (2011) Dynamics of airborne influenza A viruses indoors and dependence on humidity. PloS One 6(6): e21481.
9. Shaman and Kohn (2009) Absolute humidity modulates influenza survival, transmission, and seasonality. PNAS March 3, 2009 106 (9) 3243-3248
II. Susceptibility to respiratory infection is greater when ambient humidity is low than when ambient humidity is high: citations
1. Kudo et al. Low ambient humidity impairs barrier function and innate resistance against influenza infection. Proceedings of the National Academy of Sciences, 2019.
2. Makinen et al. Cold temperature and low humidity are associated with increased occurrence of respiratory tract infections. Respiratory Medicine, Volume 103, Issue 3, March 2009, Pages 456-462
3. Eccles R (2002) An explanation for the seasonality of acute upper respiratory tract viral infections. Acta Otolaryngol 122:183–191.
4. Iwasaki A, Pillai PS (2014) Innate immunity to influenza virus infection. Nat Rev Immunol 14:315–328.
5. Chen X, et al. (2018) Host immune response to influenza a virus infection. Front Immunol 9:320.
6. Taubenberger JK, Morens DM (2008) The pathology of influenza virus infections. Annu Rev Pathol 3:499–522.
7. Bustamante-Marin XM, Ostrowski LE (2017) Cilia and mucociliary clearance. Cold Spring Harb Perspect Biol 9:a028241.
8. Oozawa H, et al. (2012) Effect of prehydration on nasal mucociliary clearance in low relative humidity. Auris Nasus Larynx 39:48–52.
9. Kudo E, et al. (2019) Low ambient humidity impairs barrier function, innate resistance against influenza infection. NCBI BioProject. Available at https://www.ncbi.nlm.nih.gov/ bioproject/PRJNA528197. Deposited March 20, 2019.
III. Applicability to COVID-19
The emergence of COVID-19 during winter in temperate zones strongly suggests that COVID-19 is similar to flu and cold viruses in its correlation with ambient humidity levels.
COVID-19 outbreaks to date have overwhelmingly been in temperate zones where indoor humidity in winter is low. To date, major outbreaks have occurred in China, Korea, Japan, Italy and Iran. Each of these outbreaks occurred in a temperate country in the midst of winter, where indoor humidity would be expected to be quite low. There are few cases and no known major outbreaks of COVID-19 in tropical and subtropical regions. Notably South America, Africa, and the Indian subcontinent have few reported cases and (as far as the author is aware) no known cases of local transmission, suggesting that the warm and humid conditions in those regions hinders COVID-19.
Singapore, notably, had what appeared to be the beginning of a major outbreak of COVID-19 around February 14, 2020. Instead the incidence of new COVID-19 infection in Singapore has since diminished dramatically and there have been no COVID-19 fatalities in that country. Most patients in Singapore who tested positive for COVID-19 have already recovered, as of this writing. This favorable outcome strongly suggests to the author that the warm and humid climate of Singapore has been protective against COVID-19 transmission and severity.
The environmental conditions of Singapore could be substantially replicated through indoor humidification, especially to 50% relative humidity or higher, and in this way major reductions in COVID-19 transmission and severity can be achieved in other countries.
IV. Preparing for Seasonal Re-Emergence
As noted, evidence available so far strongly suggests that COVID-19 contagiousness and severity are strongly dependent on ambient humidity levels, and thus COVID-19 occurrence is expected to diminish during the summer months.
However, re-emergence of COVID-19 during the winter of 2020-2021 is likely as indoor humidity levels in the Northern Hemisphere again drop. The author hopes that a COVID-19 vaccine will be available and in wide distribution by that time. This may require a reduction in the regulatory hurdles that slow the development of vaccines in the United States and elsewhere.