Note: Updated 23rd of May 2021. Updated the URL to our peer-reviewed and published study

Since March 2020, together with scientists from Agder University (Oslo) and Hariri (Lebanon), I have been conducting full-time research into the spread of Respiratory Viruses; Influenza and SARS-CoV-2. By collaborating and sharing knowledge with, among others, scientists and professors from Cambridge, Harvard, Yale, Columbia Tech, Virginia Tech, TU Delft and the VUmc, we not only were able to conclude conclusively what the impact of Specific Humidity (q) and Solar Radiation (Q) was on the spread of respiratory viruses, Influenza and SARS-CoV-2, but we were also able to create a set of protocols that can reduce the spread of SARS-CoV-2 and the impact of COVID-19.

This research therefore shows an indisputable relationship between the spread of ‘Envelope Viruses‘ – Influenza and SARS-CoV-2 – and weather influences, Humidity (q). These conclusions, in our paper Environmental risk factors of airborne viral transmission: Humidity, Influenza and SARS-CoV-2 in the Netherlands are widely supported by fellow scientists from various universities.

Fig. 1. Humidity (q) 2017 and Influenza numbers (source dates: Nivel and KNMI)
Fig. 2. Humidity (q) 2018 and Influenza numbers (source dates: Nivel and KNMI)
Fig. 3. Humidity (q) 2019 and Influenza numbers (source dates: Nivel and KNMI)

Above you will find 3 graphs. Here you can see:

  • Influenza numbers p/week, per 100K inhabitants, (blue bars) – Scale on the left
  • Specific Humidity (q) De Bilt (red line) – Scale on the right
  • Humidity Colour bands (Red  < 6 g/kg,  Orange  7-8 g/kg,  Green  > 8/g/kg).

In support of the research results, I would also like to draw your attention to the fact that in September 2017 the weather phenomenon “La Niña” occurred. This brought with it a lower temperature (and therefore lower humidity). Remarkably, the Netherlands experienced a severe flu wave in 2017/2018. According to the U.S. Department of Commerce/National Oceanic and Atmospheric Administration (NOAA), there was a 60% chance that “La Niña” would develop again in the fall and continue through the winter period 2020-2021. Managing humidity is therefore a (cost)effective measure to contribute to “flattening the curve“. Many scholars now notice a relatively high prevalence, correlating with an extended period of low Humidity.


Spread of respiratory viruses is extraordinarily complex. Many factors have an impact on the spread of respiratory viruses. Not least; (travel) behavior of the population. The effect of measures, such as ‘hygiene’ and ‘social distancing’, also have a direct effect. Research into Influenza enabled us – with the help of CBS – to establish a base-line model value in which behavior of the population had no influence. According to national statistics bureau of The Netherlands (CBS), this was found to be almost the same during those years. In other words; the monthly mobility behavior of the population hardly appears to change. As a result, the influence of the weather on the spread of respiratory viruses could be more accurately determined.


We have also been able to accurately predict spreading of SARS-COV-2 on numerous continents, including the Island of Curacao. A few examples of our accurate predictions (mentioning an error margin of 1 week):

  • The start of the ‘Second Wave’ in Australia on July 1st, 2020;
  • Coronavirus ‘Hotspots’, in The Netherlands, in the 3rd week September 2020;
  • The start of the ‘Second Wave’, in The Netherlands, in week 44 (End of October) 2020;
  • Increase in infection- and hospitalization rates, in week 47 (1/2 November) 2020;
  • The ‘Lock-down’ measure, in The Netherlands, in week 48/49;
  • Increase in cases on the island of Curacao, based on rainfall.

This not only proves that SARS-CoV-2 spreads mostly through the air, based on levels of Specific Humidity (q) and partly on Solar Radiation (Q) but it also gives us an indication of what is to come.


The specific humidity (q) has several consequences for infection with both ‘Enveloped Viruses‘, Influenza and SARS-CoV-2:

  1. The ‘respiratory droplet’ partially evaporates at low humidity. This makes it lighter and allows it to float for a longer period. This droplet then converts, as it is often called in the media, into an ‘Aerosol‘. The lower the specific humidity (q), the lighter the droplet and the longer it can float. The more of these ‘Aerosols’ we breathe in, the higher the ‘Viral Load’ and the greater the chance of becoming infected. All of this is also related to the existing prevalence of the virus.
  2. In addition to the ‘viral particles’ (also referred to as ‘Virions’), ‘respiratory droplets‘ also contain ‘salts‘. Colleagues, Professor Linsey Marr and Dr. Wan Yang, have discovered a striking phenomenon. When the ‘respiratory droplet‘ contains a lot of water, the viral particles de-activate faster through these ‘salts‘. But these same salts form a ‘salt-shield‘ around the ‘Aerosol‘ when it evaporates/condensates at low humidity. As a result, the ‘virions’ not only remain active for longer, but this ‘salt shield‘ protects the entire ‘Aerosol‘ while being inhaled. This allows more ‘Aerosols’ pass through the mucosal mucous membranes (‘Mucosa’), increasing the ‘Viral Load’.
  3. Low specific humidity (q) also causes our mucous membranes (‘Mucosa’), our natural barrier against viruses, to ‘dry out’. Scientific research has shown that our ‘Mucosa’ is less effective when dehydrated.

We discovered the role of ‘Salts‘ through our collaboration with Prof. Linsey Marr and Dr. Wan Yang. They were the first discoverers of the effects of ‘Salts‘ in ‘respiratory droplets‘ and ‘Aerosols‘. Through our collaboration with Prof. Akiko Iwasaki, a virologist at Yale University, specializing in research into ‘Mucosal Immunity‘, we learned more about the effects of humidity on the ‘Mucosa‘. A collaboration consisting of various specialists, with various backgrounds, is proving to be highly effective. Our research shows that, in moderate climates:

Any increase in the specific humidity by 1 g/kg leads to a decrease of 5% in infections.


We discovered a pattern in South America: Increased Influenza cases during periods where there was less sunlight. For example: one research paper suggests that Influenza Infection Cases increased during the yearly burning of sugar-cane fields. A noticeable increase in smog is registered during those periods. Thereby reducing Solar Radiation (Q), explaining the increase in cases. To be clear, Q has – similar to Humidity – multiple effects. As written in this 2005 research paper, UV radiation from the sun is the primary germicide in the environment. But Q, as pointed out in this research paper, also has an effect on the production of Vitamine D. We hypothesize that the combination of Humidity (q) and Solar Radiation (Q) marries both the Influenza patterns in South America and Europe. During rain showers there is significantly less Solar Radiation (Q).


Through further research into the spread of respiratory viruses in Brazil, we found that Solar Radiation (Q) also influences the spread of respiratory viruses, Influenza and SARS-CoV-2. Solar radiation has a deactivating effect on ‘Virions‘. It should be noted that ‘peer-reviewed’ publications have already indicatedthat ‘Solar Radiation’ (Q) has a direct effect on the production of Vitamin D and that Vitamin D levels are very decisive in terms of infection and disease. We also refer to these studies in our publication of august 2020.

Our conclusions, meanwhile, are further supported by a peer-reviewed study just published March 30th in leading Journal ‘The Lancet‘. The title: “Vitamin D supplementation to prevent acute respiratory infections: a systematic review and meta-analysis of aggregate data from randomised controlled trials“.  The study can be found here:

Noting the above is important because climatologically Islands, in tropical regions, such as Curaçao, have more similarities with Brazil than countries with a moderate climate, such as the Netherlands. In past years we have seen numerous outbreaks in Brazil when there are rain showers. From research in Brazil, we can see that an extremely high humidity (Relative Humidity of 100%), during rain showers also leads to the floating of ‘Respiratory Droplets‘. In layman’s terms; during a rain shower the air is completely saturated with large droplets. So much so that the weight of a ‘Respiratory droplet‘ no longer causes it to fall to the ground. During rain, a dangerous ‘Cocktail‘ is created of (i) people close to each other, (ii) stagnant air, (iii) lack of solar radiation (Q) and (iv) an extremely high humidity. The above has been confirmed in a study recently:


On march 19th there were elections on the island of Curacao. The current epidemiological team of Curacao has stated, on numerous occasions, that the increased prevalence – that nearly overloaded the healthcare system – was because of these elections. However the data clearly shows a different story. As you will note from the graph below, incidence of positive SARS-COV-2 correlated exactly 8 days after rain showers, on the island of Curacao. The 8 days is related to the incubation period of 5-6 days and testing and confirmation, after infection. The prevalence started increasing after rain showers, well before the elections.

That is why ‘Air Purification‘, in combination with dynamic ‘Humidification‘ (in areas with Air Conditioning) are the appropriate solutions for Islands, in tropical regions. I would like to add that the risk of infection, via ‘Aerosols‘ in the open air, is virtually zero (odds of 1 in 1.000, according the ‘peer reviewed’ research from the university of Canterbury). Especially when there is a bright sun.

In the meantime, 9 months later, our research has finally gone through the peer review process. Our study has been published in Spatial and Spatio-Temporal Epidemiology. A scientific journal specializing in Epidemiology (scientific study of the occurrence and spread of diseases within and between populations). The Journal is published by Elsevier. It should be noted that managing awareness related to ‘Aerosols’ will prove very effective. For example; the population will understand why communal toilets (causing “superspread events’) should be avoided.


Recent scientific research has given rise to concerns related to vaccination. A study that has been published recently indicates that individuals lose antibodies within 4-5 months. Other researchers indicate concerns that mass-vaccination strategies could result in pressure on the SARS-CoV-2 to enhance mutation capabilities, thereby resulting in VoC (Variant of Concern) that can escape immune defenses. We already see VoC’s which escape vaccination immunity as well.


The Pfizer COVID-19 Vaccine Phase 3 study showed an efficacy of 95%. The vaccine protected 95% of the people against infection. The Johnson & Johnson Single-Shot Janssen COVID-19 Vaccine Phase 3 Trial showed an efficacy of 66%. A significantly lower number. Does this mean that J&J is worse compared to Pfizer? NO! To say that would be to compare apples and oranges.

When the Pfizer vaccine was being trialed, the original virus (also called the wild type) was the variant it was trialed against. By the time the J&J was trialed other variants were already ‘prevalent It is widely assumed – and research suggests – that all vaccine efficacies drop with the introduction of new and different variants. A recent article from Harvard Medical School, called “ Escape Artist “, notes:

“The study results could also offer a preview into a future, in which current vaccines and treatments may gradually lose their effectiveness against next-wave mutations that render the virus impervious to immune pressures”.

A Israeli study, as published on Reuters states that:

“The coronavirus variant discovered in South Africa may evade the protection provided by Pfizer/BioNTech’s COVID-19 vaccine to some extent, a real-world data study in Israel found, though its prevalence in the country is very low and the research has not been peer reviewed”.

So these Variants of Concern (VOC), such as the “South African Variant“, may be able to escape certain immune defenses.


Our epidemiological research also leads to the believe that a delicate balance of prevalence (percentage of infected individuals vs. the total population) vs. measures should be considered and managed based on data analysis expertise and not by healthcare professionals, with limited data analysis expertise. A good example for this is the comparison between the Islands; Aruba, Curaçao, and St. Maarten. You will notice that the prevalence was lower on Curaçao, whereas the prevalence was higher on both Aruba and St. Maarten. The consequence however is that the healthcare system on Curaçao was overloaded in April 2021. From the data we can conclude that Curaçao enacted a policy of measures that was too strict and resulted in the overload of the health care system. A system of dynamic policies based on prevalence levels should be considered. We have developed such a system, which has been enabled in The Netherlands.


We are concerned that a ‘perfect storm’, due to arrive in October 2021, is on the horizon. This storm will consist of a few factors, being: (i) Mass vaccination, leading to a simultaneous loss of immunity. (ii) Combined with the introduction of a variant that enables immune-escape and (iii) the rainy season in October 2021 that will increase prevalence, thereby overloading the health care system again. This can also result in social unrest.

This prediction is not merely based on data, but rather based on existing experience. The overloading of the health care system on the island of Curaçao in April 2021 was also due to a ‘Perfect Storm’. A combination of (i) earlier public health interventions that resulted in a low ‘herd immunity’ levels. Coupled with (ii) the introduction of a new variant (B.1.1.7), (iii) easing of restrictions and (iv) introduction of a massive vaccination campaign and (v) rain showers. 

We conclude that ‘Perfect Storms’ can be avoided with the following recommendations:

  1. Border control measures at ‘ports of entry’ are remarkably effective measures (see Haiti);
  2. Public Health Interventions should be based on data analytics expertise;
  3. Using Tracking & Tracing technology, cost effective and efficient;
  4. Sole reliance on (mass) vaccination is brings the risk of a ‘single point of failure’;
  5. Prevention strategies that include ‘Humidification’ and ‘Purification’ are cost effective;
  6. Public Health Interventions should take rain into account;
  7. Public Health Interventions should take ‘Aerosols’ into account;
  8. Improving ‘Public Awareness’ related to transmission via ‘Aerosols’ should be enacted

If you appreciated this post we encourage you to support our initiative of “building a weather radar that protects against COVID-19“. You can support our initiative at:

Edsard Ravelli