The diagram above is called the disease triangle. For Covid-19, the pathogen is the virus, and the host is humans or the body’s organs susceptible to the disease. We know now it is not strictly a respiratory problem. Environment can be considered the conditions by which transmission is possible or likely. When Covid began, there was an immediate need to know how Covid invades the body and replicates. Thus, the Host – Pathogen axis was critical. Equally important was knowledge of under what conditions the disease could spread, thus Pathogen – Environment axis became important. Large gatherings of people in airports, bus and train stations, and for events, such as sporting or musical events were obvious venues for disease dispersion.
Many would include a fourth element, which would be “Human Response.” I think the fourth vertex is critical in Covid. The medical response is to find ways to interfere with a disease’s growth and spread, through effective treatments and vaccines. The Covid susceptibility is much lower in countries where there is a high level of vaccination. I believe easy access to testing and rapid results allows individuals to self quarantine and seek medical assistance.
The pathogen is not constant. The delta variant spread globally with lightening speed, and the downward trend in new cases has been reversed, with increases in many countries including the US. The understanding of the infection process is still evolving with the long term damage, termed “long Covid.”
There is a commonality in the global deadly viruses, which is asymptomatic characteristic of the disease and ease of transmission. A healthy person can be a carrier of the Covid even though there are no obvious symptoms. They are unlikely to be tested in this early phase of the disease. Covid can be transmitted either directly from someone else or from touching surfaces.
The human response has a sociality aspect as mass vaccinations need cooperation. The negative aspect is clear: vaccination hesitancy, resistance and ignorance. Misinformation via social media and politics are playing negative roles. The Trump and Biden administrations are to be commended for an incredibly rapid and effective roll out of vaccines. See former Secretary of HHS, Alex Azar comments on vaccines in links.
The human response should mean we act together in accepting restrictions, including indoor mask wearing, as it is now both a necessity and temporary. Further, we need to recognize this as a pandemic and help countries which can not afford vaccines for their populations. Otherwise, the disease will continue to re-appear in the US. We don’t know how long the immunizations will last for or what new variants might appear in the future. So, we can’t accept just reducing the new cases to a low level in the US.
We have to accept the new medical information, which is the Delta variant is spreading and new cases are on the rise. It is not as dramatic, but the cases of people in the US dying of Covid have also been rising in the last 30 days.