Talk:Origin and global diffusion of the pandemic

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The COVID-19 pandemic in Spain. First wave: from the first cases to the end of June 2020

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Thematic structure > Global context of the COVID-19 pandemic > Origin and global diffusion of the pandemic

SARS-CoV-2 virus, known as COVID-19, was declared a health emergency towards the end of 2019 following an outbreak in the Chinese city of Wuhan. However, the results of water analyses gathered later from various parts of the world suggest it was already spreading before then. It presented initially as an acute health problem that spread from the original outbreak in Wuhan to other major metropolitan regions in China, particularly Shanghai, Chongqing and the Pearl River Delta (Guangzhou, Hong Kong, Shenzhen, etc.). Analyses of this expansion from data on public transport use, particularly high-speed trains –despite the small amount of data available from China–, explain the pandemic’s rapid spread throughout its vast territory. During the final months of 2019, it appeared the spread of the infection would be limited to China and to a few of its neighbouring Asian countries. However, international airports eased its spread to the rest of the world, and the World Health Organisation (WHO) declared it a global pandemic in early March 2020. The spread of the pandemic may be observed on the map on the Origins and spread of COVID-19, which shows the number of cases per country and month from February to July 2020. The peak of infections was registered in early April 2020. The lack of effective treatments for severe cases and little knowledge of how COVID-19 was transmitted during that period meant that it proved to be a highly lethal disease that resulted in tens of thousands of deaths. However, the severe lockdowns applied in many countries succeeded in gradually reducing the amount of deaths from that first wave.

The spatial diffusion of the pandemic across continents followed a predictable pattern. Initially, the virus spread from China to the rest of Asia. However, the strict lockdown measures adopted by some countries curbed the increase in infections there. Subsequently, the virus reached Europe, where it spread rapidly and soon reached the maximum number of infections in absolute terms. Later, COVID-19 was spread to the Americas, where it quickly spread. In fact, the Americas were the hardest hit continents, only lagging behind Europe for a few weeks. Finally, the pandemic also extended to the other continents yet with a much lower incidence, as happened in Africa, for example. There is, however, a possibility that the apparent lower prevalence in Africa may owe more to a lack of effective recording and to the fact that this new virus was just one more health problem in societies that are already highly vulnerable to all kinds of infectious and contagious diseases.

  • Statistical graph: Evolution of COVID-19 cases worldwide. 2020. World.
  • Statistical graph: Evolution in the number of deaths from COVID-19 worldwide. 2020. World.
  • Statistical graph: Evolution of COVID-19 cases by major regions of the world. 2020. World.
  • Statistical graph: Evolution of COVID-19 cases in most affected countries. 2020. World.
Map: Origins and spread of Covid-19 in China. 2020. China. PDF. Data.
Map: Origin and spread of COVID-19. 2020. World. PDF. Data.

When analysing the spatial diffusion by country, it is helpful to differentiate the results in absolute and relative terms. On the one hand, China went from being the origin of the infection to playing a very discreet role in the global ranking. In absolute terms, the United States ranked as the world leader in terms of the total number of patients from the end of March 2020, with Brazil ranking second behind it. These two countries, with over 500 million inhabitants between the two, have clearly topped all statistics in absolute terms since then. By contrast, in relative terms, Chile and the European States most impacted during the first wave, such as Belgium, Spain and Sweden, stand out for their high incidence amongst smaller populations. In other large countries, such as Russia and India, cases evolved in an ascending pattern before reaching a certain level of control, and they were amongst the top five countries for the total amount of infections throughout the whole period under study.

Having analysed the origin and expansion of the pandemic worldwide, the following paragraphs deal with its magnitude. In this context, three key aspects shall be evaluated in order to understand the scale of the problem: the number of COVID-19 cases recorded from January to June, the amount of deaths and the number of healthcare workers.

Map: Healthcare workers. 2018. World. PDF. Data.

The number of COVID-19 cases shall also be analysed in absolute and relative terms. In absolute values, the countries with the highest amount of recorded cases during the first wave of the pandemic were the United States, Brazil, India and Russia, which is consistent with their large size. However, what is striking is that some other countries with less than 70 million inhabitants also featured at the top of the list, including the United Kingdom, France, Italy, Spain, Chile, Peru and Saudi Arabia. The large amount of cases in these countries could be attributed to the high demographic densities in their urban areas, which are home to a sizeable part of their population, and the lack of an effective response to the outbreak during the initial weeks of the pandemic that allowed the virus to spread. In relative terms, the countries with worst data are the United States, Panama, Brazil, Peru, Chile, Spain, Belgium, Luxembourg, Ireland, Sweden, Belarus, Armenia, Kuwait, Qatar, Oman and Saudi Arabia, some of which are also amongst those worst affected in absolute terms. It shall be noted that the governments of some countries, such as the United States, Brazil and Belarus, showed some initial scepticism towards the threat of the pandemic and failed to take decisive measures to contain the spread of the virus. The evolution of the pandemic in Sweden, for example, was probably influenced by the implementation of deliberately lax lockdown measures that sought to seek a supposed herd immunity. At the opposite end of the scale, countries with fewer relative cases of COVID-19 fall into one of two categories: either they applied stringent isolation measures with exemplary levels of compliance from their populations, i.e., China, South Korea, Japan, Taiwan, New Zealand and Australia, or they have poor levels of record-keeping, and COVID-19 is present alongside other infectious and contagious diseases (ebola, malaria, yellow fever, etc.), i.e. sub-Saharan Africa and some countries in South America and Asia.

Map: COVID-19 cases. 2020. World. PDF. Data.

The amount of deaths from COVID-19 during the first wave of the pandemic was influenced by several factors, including scant knowledge of the new virus, the shortage of medical and infection prevention equipment, the absence of specific medical treatments, etc. As a result, the mortality rate stood at 5% during the initial months but decreased from June 2020 due to improved treatments and Personal Protective Equipment (PPE) availability. Given that nearly 80% of those who died worldwide were men over 70 and women over 80, the age distribution of the population was another factor to have a considerable bearing on the countrywide outcome. It is in this context that the world map of relative mortality shall be understood, in which there are five Western European countries (the United Kingdom, Italy, Spain, Belgium and Sweden) with a high mortality rate per 100,000 inhabitants due to their older age-sex pyramids and despite their solid health services, which were caught unaware during the first few months of the pandemic. At the opposite end of the scale, China (although many authors question the reliability of their data), Asia in general and Africa may be found, yet younger populations shall be borne in mind.

Map: Deaths from COVID-19 . 2020. World. PDF. Data.

With regard to healthcare workers, it is important to clarify two aspects: firstly, the data compiled by the United Nations for individual countries is for different years between 2010 and 2018; secondly, only doctors and nurses have been counted as healthcare workers, excluding other job categories in this sector, such as clinical assistants, pharmacy workers, etc. The main takeaway that may be extracted from this map is the sharp contrast between north and south. The north includes Europe, North America, Oceania, some of the Latin American countries and the Arab World. Indicators in this area are high both in absolute terms and relative to population size. In addition, nurses account for a large proportion of their total number of registered healthcare workers. This situation is especially true for Norway, Sweden, Finland, Germany, Switzerland, the United States, Chile, Lithuania and Belarus (these last two countries possibly as a legacy of the Soviet model). China, India and some Latin American countries have intermediate values for the number of healthcare workers relative to population size. In the south, by contrast, sub-Saharan Africa has the lowest availability of healthcare workers, with the few exceptions to this general rule being Botswana, Zambia, Gabon and Ghana.


      SSpread of a new disease at a certain speed, widely and simultaneously throughout several geographical areas of the world. The World Health Organisation (WHO) declared COVID-19 a pandemic after more than 100 countries officially registered cases of the disease.


      Family of viruses that affect some mammals, including humans. Some coronaviruses do not pose a threat to the health of humans. However, COVID-19 causes severe acute respiratory syndromes, attacks the lungs and may cause pneumonia. It may also cause gastric disorders and the loss of smell and taste.


      Spread, expansion or dissemination of a phenomenon over space and time. For the diffusion process to materialise, there must be a central source from which the phenomenon originates, a set of potential receptors, communication channels between the source and the receptors, and a variable period of time. The diffusion process passes through nodal points and may involve a spread that is either random, similar to that of an oil slick, or hierarchical. Spatial diffusion models came into widespread use following the work of Swedish geographer T. Haggerstränd in 1968.


      Community transmission is said to be present when a virus is detected in several people within a specific population or territory, and the origin of the infections are unknown. In the case of COVID-19, community transmission was detected when various people were tested positive for the disease after having recently visited China and other areas where the virus was spreading. This type of transmission denotes that the virus has been widespread in the community yet gone undetected for some time. When there is community transmission, the spread of the virus is deemed to be uncontrolled.


      Percentage of COVID-19 tests that come back positive out of the total amount of screening tests performed. A pandemic is deemed to be under control if this percentage lies under 5%. A positivity rate over 5%, on the other hand, suggests many people are unaware they are infected and therefore community transmission exists and screening is required. The general consensus is that this indicator offers a more accurate assessment of the risk of infection than the daily number of positives as the number of screening tests performed may vary from day to day, whilst the positivity rate is a relative value that may always be used to compare different periods as long as the testing criteria remain the same.


      Number of detected cases of a disease in a given period and specific area or community. It could also be described as the probability that a person from a specific population will be affected by said disease. In addition, the incidence rate represents the speed at which new cases of the disease appear in the exposed population. It is calculated by dividing the number of new cases of the disease by the number of inhabitants. Lastly, the cumulative incidence is the proportion of people who fall ill in a given period of time. It is calculated by dividing the number of registered cases by the amount of people who were free of the disease at the beginning of the period. It is usually calculated for every 100,000 inhabitants in periods of 7 to 14 days.


      Extraordinary and emergency measure involving the temporary isolation of an individual, group or entire population for health or safety reasons. It involves restricting movements of the population in the affected area and closing leisure, tourism and cultural facilities. It may be a full restriction in very extreme cases, yet it is mostly not so strict and travelling is allowed to varying degrees for buying food and pharmaceutical products, for work, to provide care and in case of emergency.


      A person’s general level of resistance to or protection from an infectious disease or toxin. It is linked to the presence of antibodies or cells that act specifically against the microorganism that causes the infection. There are two types of immunity: active immunity, which usually lasts for years and is acquired naturally, as a consequence of an infection, or artificially, through a vaccine; and passive immunity, which has a short duration (from a few days to several months), and is obtained naturally, by maternal transmission, or artificially, by inoculating specific protective antibodies. The term ‘herd immunity’ is widely used to describe a situation in which a high proportion of a population has immunity and, therefore, the agent is less likely to spread.


      The acronym PCR stands for polymerase chain reaction. It is a type of test used to detect infections. It consists of extracting genetic material from a sample and comparing it with the genes found in viruses (for example, in SARS-CoV-2). The test involves inserting a swab (cotton bud) into the nose or mouth of the person suspected of being infected to collect a sample. If the PCR technique does not detect the virus's genetic material, it is likely the person is not infected. The antigen test entails introducing a toxic molecule to the sample that generates an antibody reaction, enabling inferring whether the subject is infected by the virus.


      Term used to describe the imposition or recommendation that people keep a physical distance between themselves and anyone with whom they do not share a home. Its purpose is to prevent transmissions. This measure has become the most effective tool for containing the spread of COVID-19, especially when community transmission exists.


Co-authorship of the text in Spanish: Agustín Gámir Orueta, Rubén C. Lois González, Ángel Miramontes Carballada and Ana Paula Santana Rodrigues. See the list of members engaged

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You can download the complete publication The COVID-19 pandemic in Spain. First wave: from the first cases to the end of June 2020 in Libros Digitales del ANE site.