Every year, we have a well defined flu virus season. It starts in the Fall, builds in the Winter, then peaks as temperatures warm up in the Spring.
Exact same thing happens in the Southern Hemisphere.......exactly 6 months later timed exactly to their seasons, just like ours.
This is not a coincidence. It happens like that every year. There have been several attempts to try to explain this, including more contact between people because they spend more time indoors.
One element that affects virus's that much of science and medicine agree on is related to the weather.
Turns out, that virus's can stay in the air longer and spread more effectively when its cold and dry outside.
Temperatures inside might be warmed up from heating but the air outside is very day/has little moisture and is brought inside, then warmed up air and is even drier.
It appears that warm AND HUMID is the most unfavorable for MOST virus's.
Because of this, we have the strong/reliable seasonality for the flu virus.
metmike: Low moisture/humidity, which is what we get inside during the Winter after taking in the cold dry air outside and heating it up = VERY favorable for virus survival.
Higher moisture environments, which exist with warmer temperatures, especially because warm air can hold much more moisture = UNfavorable for virus survival.
When it warms up in the northern hemisphere this Spring and especially into Summer's heat, the environment will possibly become much more UNfavorable for the Coronavirus.
This particular study is extremely promising.
Using the daily R values from January 21 to 23, 2020 as proxies of non-intervened transmission intensity, we find, under a linear regression framework for 100 Chinese cities, high temperature and high relative humidity significantly reduce the transmission of COVID-19, respectively, even after controlling for population density and GDP per capita of cities. One degree Celsius increase in temperature and one percent increase in relative humidity lower R by 0.0383 and 0.0224, respectively. This result is consistent with the fact that the high temperature and high humidity significantly reduce the transmission of influenza. It indicates that the arrival of summer and rainy season in the northern hemisphere can effectively reduce the transmission of the COVID-19.
Using the value R to represent the transmission, the paper also found that cities in northern China, where temperatures and relative humidity were lower, had larger transmission values than cities along the country's southeast coast.
The scientists' findings align with what some experts have suspected about weather's impact, including Hong Kong University pathology professor John Nicholls, who told AccuWeather that research on a lab-grown copy of SARS-CoV-2, "in cold environments, there is longer virus survival than warm ones."
Total virus collected for 60 minutes retained 70.6–77.3% infectivity at relative humidity ≤23% but only 14.6–22.2% at relative humidity ≥43%. Analysis of the individual aerosol fractions showed a similar loss in infectivity among the fractions. Time interval analysis showed that most of the loss in infectivity within each aerosol fraction occurred 0–15 minutes after coughing. Thereafter, losses in infectivity continued up to 5 hours after coughing, however, the rate of decline at 45% relative humidity was not statistically different than that at 20% regardless of the aerosol fraction analyzed.
At low relative humidity, influenza retains maximal infectivity and inactivation of the virus at higher relative humidity occurs rapidly after coughing. Although virus carried on aerosol particles <4 µM have the potential for remaining suspended in air currents longer and traveling further distances than those on larger particles, their rapid inactivation at high humidity tempers this concern. Maintaining indoor relative humidity >40% will significantly reduce the infectivity of aerosolized virus
Washington, D.C., March 13, 2020 (GLOBE NEWSWIRE) -- What can the public do to defend against the COVID-19 coronavirus? One simple answer is to ramp up humidification at home and in the workplace, if humidity levels are low. Hospitals treating cases of viral respiratory infection may be advised to do the same.
Why has the novel coronavirus COVID-19 had only a minimal impact in tropical countries while temperate zone countries such as China, Korea, Italy, Iran and the United States have suffered outbreaks? Humidity, and especially indoor humidity, seems to hold the key.
metmike: It's a Different Coronavirus below that does poorly when we warm up and add moisture. Warm and dry does not hurt the virus nearly as much as warm and humid.
COVID-19 probably will act in similar fashion.........but not for sure.
Spread of SARS-CoV-2Coronavirus likely to be constrained by climate
Not all viruses are climate determined. HIV/AIDS, for example, is not affected by external environmental factors. The virus is transmitted by sexual intercourse, blood transfusions, orfrom mother to child during pregnancy,delivery or breastfeeding,so it never leaves the host’s internal environmental conditions. In contrast, SARS-CoV-2, like other respiratory viruses, namely its predecessor SARS-CoV, involves aerial transmissions of respiratory droplets or fomites, exposing the virus to external environmental conditions. SARS-CoV-2 Coronavirus has already set foot in most parts of the world, but virulent outbreaks with large numbers of localinfections are still not global. Instead, outbreaksconcentrate in the northern hemisphere, chiefly Asia, the Middle East, Central, Southern and Western Europe, and the USA. Our models support the view that the incidence of the virus will follow a seasonal pattern with outbreaks being favored by cool anddry weather, while beingslowed down by extreme conditions of cold and heat as well as moist. Prevalence of respiratory diseaseoutbreaks,such as influenza, during wintering conditions is common16,17. But the similarity of climate determination of SARS-CoV-2 with its predecessor SARS-CoV is noteworthygiven hope that fundamental traits shared by the two Coronavirus might be conserved. Analyses of SARS-CoVoutbreaks in relation to meteorologyrevealsignificant correlationsbetween the incidence of positive cases and aspects of weather.For example, aninitial investigation linking SARS outbreaks and temperature in Hong Kong, Guangzhou, Beijing, and Taiyuan18, revealed significantcorrelationsbetween SARS-CoV incidences and temperatureseven days (the known period of incubation of SARS-CoV) before the outbreak,with environmental temperaturesassociated with positive cases of SARS-CoV ranging between 16ºC to28ºC. They also found that incidence of the Coronavirus was inversely related to humidity. Another study conducted between 11 March and 22 May 2003 in Hong Kong19showed that SARS-CoV incidences sharply decreased as temperature increased from 15ºC to 29ºC,after whichit practically disappeared. Inthis study, . CC-BY-NC-ND 4.0 International licenseIt is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not peer-reviewed) The copyright holder for this preprint .https://doi.org/10.1101/2020.03.12.20034728doi: medRxiv preprint 6incidences under the cooler end of the gradient were 18-fold higher than under the opposite warmerendof the gradient. The mechanism underlying these patterns climate determination is likely linked with the ability of the virus to survive external environmental conditions prior to reaching a host. For example, a recent studyexamined survival of dried SARS-CoV Coronavirus on smooth surfaces and found that it would be viable for over 5 days at temperatures ranging between11-25ºC and relative humidity of 40-50%, drastically loosing viability as temperatures and humidity increased20. Heat intolerance of the Corona viruses is probably related to their being covered by a lipid bilayer21,22, which could breakdown easily as temperatures increase. Humidity inthe air is also expected to affect the transmissibility of respiratory viruses.Once the pathogens have been expelled from the respiratory tract by sneezing, they literally float inthe airand theydo so for a longer period when the air is more humid.
metmike: You would think., based on that last statement that higher humidity would increase transmissibility but its the opposite.
Temperature and latitude analysis to predict potential spread and seasonality for COVID-19
Researchers at the Institute of Human Virology (IHV) at the University of Maryland School of Medicine (UMSOM) and the Global Virus Network (GVN) predict that the novel coronavirus (COVID-19) will follow a seasonal pattern similar to other respiratory viruses like seasonal flu. They base this on weather modeling data in countries where the virus has taken hold and spread within the community.
This map reflects average temperature data from March 2019 to April 2019 to predict the at-risk zone for community transmission of COVID-19. The zone at risk for significant community spread in the near term includes land areas within the green bands, outlined in dark black, but may change based on actual average temperatures in 2020 during this time period. (Image from Climate Reanalyzer)
In a new paper published on the open-data site SSRN, the researchers found that all cities experiencing significant outbreaks of COVID-19 have very similar winter climates with an average temperature of 41 to 52 degrees Fahrenheit, an average humidity level of 47 to 79 percent with a narrow east-west distribution along the same 30-50 N” latitude. This includes Wuhan, China, South Korea, Japan, Iran, Northern Italy, Seattle, and Northern California. It could also spell increasing trouble for the Mid-Atlantic states and — as temperatures rise — New England.
“Based on what we have documented so far, it appears that the virus has a harder time spreading between people in warmer, tropical climates,” said study leader Mohammad Sajadi, MD, associate professor of medicine, UMSOM, physician-scientist at IHV, and a member of GVN.
These are the temperature anomalies for the 6-10 and 8-14 day period coming up.
ArchivesAnalogsLines-Only FormatGIS Data
Some places should warm up enough to possibly make the environment less favorable for COVID-19 to spread during April.
Higher humidity with the warmth are best at stifling most virus's.
1. It's not a certainty that COVID-19 will display the same seasonal tendencies as the flu or other coronavirus's.
2. Even if it does diminish this Summer because of the weather, the virus will not die out completely. Since there won't be a vaccine in the Fall, it likely means an attempt at a comeback for COVID-19.
3. By then, we will all be familiar enough with it and witnessed that it only killed a fraction of the people that flu does, so round 2 of COVID-19, should it occur, starting next Fall, will be without the extreme panic of round 1 that featured scary unknowns about worst case scenarios about how bad it would get and how long it would last.
While experts know that cold temperatures and low humidity promote transmission of the flu virus, less is understood about the effect of decreased humidity on the immune system's defenses against flu infection.
Lab experiments, for instance, have looked at the way flu spreads among groups of guinea pigs. In moister air, the epidemic struggles to build momentum, whereas in drier conditions it spreads like wildfire. And comparing 30 years’ worth of climate records with health records, Jeffrey Shaman at Columbia University and colleagues found that flu epidemics almost always followed a drop in air humidity.
In fact, the overlap of the graphs was so close, “you could pretty much put one on top of each other,” says Metz, who together with Adam Finn, recently reviewed all the evidence for the Journal of Infection. The finding has now been replicated many times including analyses of the 2009 Swine flu pandemic.
Much of the observed wintertime increase of mortality in temperate regions is attributed to seasonal influenza. A recent reanalysis of laboratory experiments indicates that absolute humidity strongly modulates the airborne survival and transmission of the influenza virus. Here, we extend these findings to the human population level, showing that the onset of increased wintertime influenza-related mortality in the United States is associated with anomalously low absolute humidity levels during the prior weeks. We then use an epidemiological model, in which observed absolute humidity conditions temper influenza transmission rates, to successfully simulate the seasonal cycle of observed influenza-related mortality. The model results indicate that direct modulation of influenza transmissibility by absolute humidity alone is sufficient to produce this observed seasonality. These findings provide epidemiological support for the hypothesis that absolute humidity drives seasonal variations of influenza transmission in temperate regions.
"In addition to having an effect on the virus, temperature andhumidity may affect the host side of the host-pathogen equationby altering susceptibility to influenza virus infection or the courseof disease following infection. Cooling of the nasal epitheliumthrough inhalation of cold air has been shown to inhibit muco-ciliary clearance and may limit phagocytosis by innate immunecells resident in the upper airways (13). Similarly, inhalation of dryairfor a 30-min period was found to slow mucociliary clearancesignificantly (15). Both cold air and dry air are thought to alter therheologicalproperties of mucus (13,15). At lower temperatures,cellularmetabolic functions are also slowed, which in turn maydecrease the frequency of ciliary beats, reduce mucus secretion,and restrict phagocytosis (13).Finally,environmental conditions may impact transmission through effects on the vehicle itself, the respiratory droplet. Thelength of time a droplet remains airborne, and therefore availablefor inhalation, is dependent on its size: droplets of20mindiameter settle out of the air rapidly, whereas those of5mremain airborne for prolonged periods (16). Evaporation of waterfromrespiratory droplets, which occurs more rapidly with declin-ing RH, decreases droplet size and therefore increases the distanceand time over which transmission can occur.Thus, cold and/or dry conditions impact the stability of influ-enza virus particles, the innate defense of host nasal epithelia, andthe production of infectious bioaerosols. Each of these effects con-tributes a plausible explanation for the impact of RH and temper-ature on respiratory droplet transmission, and more than onemechanism most likely contributes to the observed transmissionoutcomes.Meteorological predictors of influenza virus outbreaks.Totest whether the observed impact of environmental factors on in-fluenza virus transmission does in fact drive the seasonal period-icity of influenza, a number of epidemiological studies comparinginfluenza incidence to climatic conditions have been performed.The association between the month (or months) of peak influenzaactivity and a number of climatic variables was recently assessedfor 78 localities around the globe. Analysis of average monthlytemperature, RH, precipitation, solar radiation, and specific hu-midity (a measure of AH) revealed that, at high latitudes, influ-enza peaks coincided with months of lower temperature, lowersolar radiation, and lower specific humidity. In contrast, peak in-fluenza activity in localities within 10° of the equator correlatedwith months of high specific humidity and precipitation. At inter-mediate latitudes (12.5 to 25°N/S), no significant association wasobserved. The authors concluded that, across temperate and trop-ical climates, two distinct types of climatic conditions are associ-ated with influenza epidemics: cold/dry and humid/rainy (1).Similarly,using data specific to the United States, the date of onsetof influenza epidemics was strongly associated with periods ofanomalously low absolute humidity and temperature conditionsin the weeks prior to the epidemics (17). A mathematical modelincorporatingobserved AH data, as a modulator of influenza virustransmission rates, was furthermore successful in simulating ob-served influenza-related death rates for individual states"
Volume 71, Supplement 1, June 2015, Pages S54-S58
Low absolute humidity (AH) has been associated with increased influenza virus survival and transmissibility and the onset of seasonal influenza outbreaks. Humidification of indoor environments may mitigate viral transmission and may be an important control strategy, particularly in schools where viral transmission is common and contributes to the spread of influenza in communities.
For example, mean calculated 1-hour virus survival is projected to decrease from approximately 75% during periods when indoor AH is very low (~3-4 mb) to 35% when indoor AH is raised to 10 mb, a target we demonstrate can be achieved over several hours by a classroom humidifier set to a target RH of 60% on a winter day. During late spring and early fall, indoor school AH often reached 10mb and 60% RH (data not shown). Our estimation of changes in virus survival are limited to models constructed from a single set of animal experiments; however, other experiments have demonstrated similar increases in survival at very low humidity [12, 13]. These data suggest that raising wintertime indoor AH to levels typically experienced indoors during fall and spring offers a strategy to reduce transmission of influenza in schools, and potentially the community, particularly when combined with vaccination and other non-pharmaceutical interventions [14–18]. As our measures reflect changes in 1 hour virus survival, humidification over a longer period (4 hours or longer) would afford a greater opportunity to reduce transmission more substantially. Indeed, this intervention may be particularly important when influenza outbreaks (or pandemics) due to novel influenza viruses occur and effective vaccines and antiviral medications are not available.
In temperate regions influenza epidemics recur with marked seasonality: in the northern hemisphere the influenza season spans November to March, while in the southern hemisphere epidemics last from May until September. Although seasonality is one of the most familiar features of influenza, it is also one of the least understood. Indoor crowding during cold weather, seasonal fluctuations in host immune responses, and environmental factors, including relative humidity, temperature, and UV radiation have all been suggested to account for this phenomenon, but none of these hypotheses has been tested directly. Using the guinea pig model, we have evaluated the effects of temperature and relative humidity on influenza virus spread. By housing infected and naïve guinea pigs together in an environmental chamber, we carried out transmission experiments under conditions of controlled temperature and humidity. We found that low relative humidities of 20%–35% were most favorable, while transmission was completely blocked at a high relative humidity of 80%. Furthermore, when guinea pigs were kept at 5 °C, transmission occurred with greater frequency than at 20 °C, while at 30 °C, no transmission was detected. Our data implicate low relative humidities produced by indoor heating and cold temperatures as features of winter that favor influenza virus spread.
The science seems clear on this.
Low humidity = good for virus's to spread.
High humidity =bad for virus's.
With that being the case, humidifying an environment can substantially reduce virus survival and transmission potential in that environment.
One study above, suggests that the 1 hour survival rate of a virus will drop from 75% to 35% by increasing the indoor humidity from 18-24% to 60%.
Using a humidifier at home when its cold and/or very dry outside (and that air comes inside, then heated) will cut down on virus's in the air that you and family members breathe.
However, most people are infected OUTSIDE their homes, especially with the coronavirus.
Having a humidified home during the Winter has other benefits too (besides reducing virus survival times in the air from infected family members) but it won't help much to stop illnesses that are acquired from exposure outside the home.
Based on some of these studies and comments, it's looks like a rough rule of thumb might be something like a doubling of the humidity, results in a 50% reduction in the 1 hour virus survival time.
Is the increasing numbers of new cases slowing down?
From 2 days ago:
Record temperatures continue across Florida on Sunday in the mid-90s ... so far there is scant quantitative evidence that heat + humidity will immediately halt COVID-19 but this summer weather will surely provide pertinent data.
I am so glad your research has given us a ray of hope
As farmers we can't just sit inside and avoid all normal daily jobs
Thankfully nobody in this family has to stand at a cash register all day
But we do have to plant a crop
Many things can be done to mitigate contact, such as deliveries when nobody is around etc. but our greatest fear is if our supply of inputs is interrupted by too many sick people and/or slow deliveries or none at all
It looks as if our part of the world will have above spring temps, if the forcast holds true and this should slow down the spread of the virus
Farmers being what we are, I am sure we will get a crop planted
At least we don't have to fight excessive water, so far, in this part of the world
The machinery is coming out of storage and ready to go, when the soil allows spring work here on our farm
We were wondering when things would have to open up some what
People can't stay home forever, but your research gives us a great deal of hope better times will come
One thing I noticed
In the early days of infection you could follow a line of infections clear acress the world in a narrow band
Of coarse that band has widened considerably, but earlier, it followed the upper green band on your map
If I could do a link I would post it but take my word, MM research does have a ton of good information