**8. COVID-19 scientific findings with impact on the built environment design**

The inevitable came with the COVID-19 pandemic. It led to an important allocation of resources in scientifically addressing the pandemic. Although the most notorious studies concern vaccines and antivirals, other research directions regard non-pharmaceutical measures aimed to prevent or mitigate pandemics. As in the 19th century, the implementation of some of these findings needs a **dedicated built environment approach**.

#### **8.1 Pollution**

Air pollution was already subject to studies that proved the effects on human health, such as respiratory diseases or lung cancer [29]. The correlation between road traffic, pollution and health has been associated with heart disease mortality [30].

**Studies undergone in 2020 almost unanimously found that the relationship between air pollution and the COVID-19** led to a "large increase [31]" in the US, clear increases in the Netherlands [32], to a "significant relationship [33]" in China, "aggravating [34]" in a study on nine cities form India, China, Pakistan, and Indonesia and "increase vulnerability [35]" or positively associated with higher fatality rates [36] in Italy.

#### **8.2 Green areas**

Pre-pandemic studies already concluded not only that "the percentage of green space in people's living environment has a positive association with the perceived general health [37]" but also "consistent negative association between urban green space exposure and mortality, heart rate, and violence, and positive association with attention, mood, and physical activity [38]".

**In the context of the COVID-19 pandemic, studies interpreted the distribution of green areas as part of the environment role on the infection's risks** [39]. Green spaces are also interpreted as a barometer for health inequity [39]. The green spaces help regulate the heat islands [40], generally considered as a zoonotic pandemic aggravating factor. There are studies that show how suburban forest fragmentation led to increased human disease risk.

#### **8.3 Urban population density**

Studies carried over time aimed to determine the correlation between population density and pandemics. For the 1918 Spanish flu, in England and Wales, research found "30–40% higher rates in cities and towns compared with rural areas" but "no association between transmissibility, death rates and indicators of population density and residential crowding [41]". A research on India stretches that districts with a lower density experienced lower rates of population loss [42]. A US research revealed "the positive correlation between population density and influenza mortalities [43]" although another paper finds no significant correlation between population density and transmissibility measured by the reproductive number (R) [44]. As for Japan, a paper concluded that "lower morbidity in the towns and cities is likely explained by effective preventive measures in urban areas [45]."

Other researchers investigated the correlation between population density and epidemics of tuberculosis or avian flu [46–49]. Paper also discussed on the impact of urban form and land use on the transmission of vector-borne viruses [50].

**During the COVID-19 pandemic, most of the researches consider increased population density as a health risk**. Papers in Japan concluded that "the correlations between the morbidity and mortality rates and population density were statistically significant [51]" or "the population density was shown to be a major factor [52]". In India, there was a "moderate association between Covid-19 spread and population density [53]". In Algeria, "there is a strong correlation [54]". In Turkey, "population density mediated the effect of wind speed (9%) on the number of COVID-19 cases [55]". US studies show contradictory results which must be further analyzed through different criteria. A paper concludes that "counties with greater population density have greater rates of transmission [56]". Some concluded that denser locations more likely to have an early outbreak but did not found evidence that linked the population density to the COVID-19 cases and deaths [57]. Another study pointed that "county density leads to significantly lower infection rates and lower death rates […] possibly due to superior health care systems [58]".

Those conclusions must be correlated with studies that include income, education or health care systems [36, 59]. A study involving more variables was realized in Italy, showing that population density was not statistically significant but, instead, car and firm density were positively associated with higher fatality rates [36].

These researches are limited though by the ability of collecting geolocation data. In the US and in the EU, gathering spatial data about people movements was neither intended by the governments nor embraced by citizens' free participation [60].

### **8.4 Air control**

Respiratory route transmitted diseases can spread either by droplets or by aerosols (suspensions in air of finer particles). By 2020, "virtually all infectious disease dynamics models on influenza have thus far ignored aerosol-transmission [61]".

Research conducted during the COVID-19 pandemic showed that aerosols could be one of the most dangerous way of transmission in the interior spaces. A paper concluded that "virus could be detected in aerosols up to 3 hours post aerosolization [61]". The badly ventilated rooms present the highest risk as an article on a Wuhan Hospital shows that the highest virus concentration was found in the toilets [62].

A 2020 research shows that **3 air changes per hour**, which is common in most countries legislation, "generated reductions in expected outbreak sizes that would normally only be possible with a substantial **vaccination coverage of 50–60%,** which is within the range of observed vaccination rates in school settings [63]".

Studies show also that recirculating the air without proper filtration presents a potential risk. According to the study of a closed restaurant in Guangzhou, published on 2 April 2020, "droplet transmission was prompted by air-conditioned ventilation" and therefore the virus might have traveled through the central HVAC system [64]. The finding was confirmed by the April 2020 statement of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHARE) that "infectious aerosols can be disseminated through buildings by pathways that include air distribution systems and interzone airflows [65]".
