What the latest studies say.

Coronaviruses are a group of viruses that affect the respiratory tract. Coronavirus COVID-19 developed in China from two strains of different animal origin: bat and pangolin (1) although other studies believe COVID-19 is closely related to coronaviruses derived from five wild animals, including Paguma larvata, Paradoxurus hermaphroditus, Civet, Aselliscus stoliczkanus and Rhinolophus sinicus, and was in the same branch of the phylogenetic tree. However, the genome and ORF1a homology show that the virus is not the same as the coronavirus derived from these five animals, while the virus has the highest homology with the bat coronavirus isolated RaTG13, while on the pangolin the genome affinity is still unclear (2).

Human-to-human transmission

Coronavirus COVID-19 spreads mainly through the respiratory tract with a high degree of infectivity.  Transmission via droplets is the main route (3).

Droplets can also infect the eyes (4).

Transmission from inanimate surfaces

Coronavirus COVID-19 can also spread from inanimate surfaces.

Coronavius COVID-19 in dried form remains active on inanimate surfaces for only 3 hours, while in liquid suspension form it remains active for 5-9 days (5), but it can be removed with classic disinfectants such as alcohol or hydrogen peroxide (6) (7). 

Travel-related cases were the main source of COVID-19 cases during the early stages of the current epidemic in Italy (8). this study found that 779 cases (95% CI: 632 to 967) would be exported from China by 15 February 2020 without borders or travel restrictions and that the travel blocking measures applied by the Chinese government subsequently avoided 70.5% of contagion (9).  In particular, the coincidence of the Spring Festival in China increased the volume of travel from Wuhan, Hubei Province, epicenter of COVID-19 spreading the epidemic (10).

So the most effective way to reduce transmission, peak incidence, overall mortality are: syndromic surveillance, timely isolation of patients, strict quarantine of all contacts (11), stay at home.

The use of an FFP2 (N95) or FFP3 (N99) mask only protects the nose and mouth from virus entry, but not the remaining part of the body.  The droplets move like invisible fog and thus arrive compactly over the entire face and body and can find their way in, not only through the nose and mouth, which may be covered by the mask, but also through the eyes. Therefore, the use of the mask only works when combined with specifically protective glasses. Earcup and possible skin lesions are another way in (12).  The mask is instead useful for those who are infected, in order not to disperse the droplets in the environment.  In this study, the filtering tests of the various types of masks (13). In any case, considering  the "distraction" of those who are unfortunately virus carriers and those who are healthy virus carriers, everyone should wear them. This is my opinion, after examining hundreds of studies on the subject.

References_________________________________________________

((1) Fan HH, Wang LQ, Liu WL, An XP, Liu ZD, He XQ, Song LH, Tong YG. Repurposing of clinically approved drugs for treatment of coronavirus disease 2019 in a 2019-novel coronavirus (2019-nCoV) related coronavirus model.   Chin Med J (Engl). 2020 Mar 6. doi: 10.1097/CM9.0000000000000797.

(2) Li C, Yang Y, Ren L. Genetic evolution analysis of 2019 novel coronavirus and coronavirus from other species [published online ahead of print, 2020 Mar 10]. Infect Genet Evol. 2020;104285. doi:10.1016/j.meegid.2020.104285

(3)  Han Q, Lin Q, Ni Z, You L.Uncertainties about the transmission routes of 2019 novel coronavirus.   Influenza Other Respir Viruses. 2020 Mar 4. doi: 10.1111/irv.12735.

(4)  Lu CW, Liu XF, Jia ZF. 2019-nCoV transmission through the ocular surface must not be ignored.  Lancet. 2020 Feb 22;395(10224):e39. doi: 10.1016/S0140-6736(20)30313-5. 

(5) Chan KH, Peiris JS, Lam SY, Poon LL, Yuen KY, Seto WH. The Effects of Temperature and Relative Humidity on the Viability of the SARS Coronavirus. Adv Virol. 2011;2011:734690. doi:10.1155/2011/734690

(6) Kampf G, Todt D, Pfaender S, Steinmann E. Persistence of coronaviruses on inanimate surfaces and their inactivation with biocidal agents.    J Hosp Infect. 2020 Feb 6. pii: S0195-6701(20)30046-3. doi: 10.1016/j.jhin.2020.01.022.

(7) Ong SWX, Tan YK, Chia PY, Lee TH, Ng OT, Wong MSY, Marimuthu K.  Air, Surface Environmental, and Personal Protective Equipment Contamination by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) From a Symptomatic Patient.  JAMA. 2020 Mar 4. doi: 10.1001/jama.2020.3227.

(8) Porcheddu R, Serra C, Kelvin D, Kelvin N, Rubino S. Similarity in Case Fatality Rates (CFR) of COVID-19/SARS-COV-2 in Italy and China.    J Infect Dev Ctries. 2020 Feb 29;14(2):125-128. doi: 10.3855/jidc.12600.

(9) Wells CR, Sah P, Moghadas SM, et al. Impact of international travel and border control measures on the global spread of the novel 2019 coronavirus outbreak [published online ahead of print, 2020 Mar 13]. Proc Natl Acad Sci U S A. 2020;202002616. doi:10.1073/pnas.2002616117

(10) Zhong P, Guo S, Chen T. Correlation between travellers departing from Wuhan before the Spring Festival and subsequent spread of COVID-19 to all provinces in China [published online ahead of print, 2020 Mar 17]. J Travel Med. 2020;taaa036. doi:10.1093/jtm/taaa036

(11) Wilder-Smith A, Chiew CJ, Lee VJ. Can we contain the COVID-19 outbreak with the same measures as for SARS?     Lancet Infect Dis. 2020 Mar 5. pii: S1473-3099(20)30129-8. doi: 10.1016/S1473-3099(20)30129-8

(12) Lan J, Song Z, Miao X, et al. Skin damage and the risk of infection among healthcare workers managing coronavirus disease-2019 [published online ahead of print, 2020 Mar 11]. J Am Acad Dermatol. 2020;S0190-9622(20)30392-3. doi:10.1016/j.jaad.2020.03.014

Yan Y, Chen H, Chen L, et al. Consensus of Chinese experts on protection of skin and mucous membrane barrier for healthcare workers fighting against coronavirus disease 2019 [published online ahead of print, 2020 Mar 13]. Dermatol Ther. 2020;e13310. doi:10.1111/dth.13310

(13) Mueller W, Horwell CJ, Apsley A, Steinle S, McPherson S, Cherrie JW, Galea KS.  The effectiveness of respiratory protection worn by communities to protect from volcanic ash inhalation. Part I: Filtration efficiency tests.   Int J Hyg Environ Health. 2018 Jul;221(6):967-976. doi: 10.1016/j.ijheh.2018.03.012.