Expanding and Returning Pandemic

In in the first four months of the pandemic, most potentially exposed people lived in more technologically developed areas.  They could protect themselves from the transmission routes described above: staying more than two meters from others; buying and using soap and disinfectants; defecating in effective modern toilet and sewer systems; and staying at home living on their savings.  Infected people usually spread respiratory diseases locally to people near them, then flew in airplanes to other cities in highly developed nations, starting more outbreaks.  So, people of middle and upper socio-economic statuses spread the disease multi-nationally.  Then people in each local outbreak spread it to people of lower socio-economic statuses in highly developed nations.

As the pandemic spreads, people are starting to spread COVID-19 to billions of people in less technologically developed areas, who live in crowded slums, or small rural houses.  Many can afford to buy only a little soap, must use leaking sewers or simple latrines, or defecate outside, and have access to only basic health information and care.  These living conditions and actions could compel them to transmit these viruses to hundreds of millions, killing millions (Bisen and Raghuvanshi; Burki; Chotiner; Davis; Doherty; El-Sadr and Justman; Garrett; Hargreaves et al.; Hopman et al.; Lancet; Malley and Malley; Quick; Shah; Wolfe).

Even if widespread testing, immunization, or curative treatments are not available, people’s use of social distancing and low-technology methods are reducing infections.  After the pandemic subsides in more developed communities, then people will relax their restrictions and re-start work.  The virus could return from the still infected people in more developed communities (Cyranowski).  The virus could also return from less-developed communities and nations, and transmit to millions of not-yet-exposed people in more developed communities.  So, all nations and communities will need to help each other stop this pandemic.


Research Needed Next

The information in this report shows that less is known about the COVID-19 coronavirus than other disease pathogens.  Scientific studies have proven that the SARS-CoV-2 virus is causing this pandemic (World Health Organization-China).  But no studies have yet proven the whole sequence of transmission from coronavirus COVID-19 diseased person, through viable virions in a body fluid and transmission route, to infecting and causing disease in another person (Brosseau).  Research should also be done on how transmissible the virus is in different body fluids, solid surfaces, air, and animals, and for how long, comparing the transmission routes.  These should include studies of viable viruses, like that of van Doremalen et al.  The characteristics of different kinds of infected people, including asymptomatic semi-immune people, comparing their roles in transmission, should also be studied.  The effectiveness of different prevention techniques should also be measured and compared (Brosseau; Lipsitch, Swerdlow, Finelli; World Health Organization-China; Yuen et al.).  Researchers should also ascertain the number of virions needed to infect a person via each transmission route (Khamsi; Yong E). These many studies might find that many potential transmission routes are neither completely safe nor unsafe, but have different probabilities of transmission, perhaps in the 20%-80% range. Both the public and health professionals may need to cope with these uncertainties for years.

In addition to those studies of the effects of SARS-CoV-2 on individuals, scientists should study groups’ and communities’ actions and their results.  Case histories of transmission chains should be followed up in more detail, in different populations, to compare them.  Then, for each transmission route, the basic reproductive numbers R0 should be calculated. The research methods should include cohort studies, household studies, surveillance, epidemiologic field investigations, and case series.  Household’s and workplaces’ strategies for preventing transmission should be compared and assessed.  The different methods governments and organizations started and eased quarantine and isolation restrictions, and their results, should be studied.

Since scientists in many countries are studying these topics, they should exchange information, to protect people of all nations (G-Science Academies of Science and of Medicine).



I searched PubMed, medRxiv, bioRxiv, LitCovid (LitCovid 2020), health science journals’ coronavirus center web pages, news media, and companies’ web pages, for peer-reviewed or good quality articles, preprints, research reports, and news reports specifically on transmission routes of coronavirus disease COVID-19, using the search terms “coronavirus”, “COVID-19”, “SARS-CoV-2”, “2019-nCoV”, “transmission”, “saliva”, “mucous”, “blood”, “feces”, “fecal”, “fomite”, “surface”, “droplet”, “aerosol”, “asymptomatic”, “pregnancy”, “birth”, “childbirth”, “dog”, “cat”, “sexual transmission”, “vagina”, “testes”, “semen”, and “food”.  I included original research studies of the community transmission routes of COVID-19 infected people.  I excluded publications on: nosocomial infections in health care facilities; entry into the body, pathology, medical treatment, other coronaviruses; epidemiological statistics; mathematical models and predictions; and zoonotic origins from animals.  Some news media announced summaries of original research within hours of publication, before PubMed and peer-reviewed summary articles did, so news served as quick bridges to up-to-date research.  Articles published in English, and some translated from Chinese, were included.

Researchers are publishing new articles daily, so I will continue updating and revising this web page daily.



This research did not receive any grant from funding agencies.

Eleanora Robbins, PhD, proof-read and suggested revisions for an earlier draft.


Declaration of Interests

The author declares no competing financial or personal interests.