With the adoption of a settled life, irrigation systems were developed, and people started living together as a society. Large-scale outbreaks emerged after society became agriculture-dependent, and people were affected by animal-borne diseases after coming into close contact with animals. Moreover, there were other reasons why outbreaks occurred, such as difficulties accessing healthy water, increasing dialog between people in different locations for economic, cultural, social, and military purposes, and living together after the construction of cities. Mass death numbers increased following the construction of cities in which hundreds of thousands of people live. Due to new social lifestyles, some infectious diseases started to spread rapidly.
Garbage, wastes, and dirty waters in crowded cities lead to infectious diseases and outbreaks. The other factors include seasonal characteristics, climate change, agricultural production techniques, and increasing contact with natural life following the construction of new settlements. Moreover, famines and wars have triggered outbreaks throughout history.
In particular, smallpox and measles, which caused epidemics or pandemics, were prevented by vaccines. Plague, typhus, and cholera pandemics were prevented by improving the infrastructures of living spaces. Although, favorable results were achieved with treatments and contact tracing for syphilis, tuberculosis, and malaria, an effective solution like a vaccine was not the case. The advancements in a healthy diet, vaccine, and treatment services reduced, prevented, or eliminated many diseases that led to great pains throughout history. SARS and MERS pandemics caused by coronaviruses and influenza pandemics in the 20th and 21st centuries resulted in the deaths of many people.
Health events of concern, such as outbreaks or pandemics are regularly announced by the World Health Organization.
See Table 1 for disease outbreaks of concern announced by the WHO in 2021.
| Health Events of Concern | Region-Country | Report Date (2021) |
| H1N2 | Brazil | January 4 |
| Vibrio cholerae O1 serotype Ogawa | Togo | January 4 |
| MERS-CoV virus disease | Saudi Arabia | February 1 |
| Ebola virus disease | Democratic Republic of the Congo | February 10 |
| Rift valley fever | Kenya | February 12 |
| Ebola virus disease | Guinea | February 17 |
| MERS-CoV virus disease | United Arab Emirates | March 17 |
| Human infection with avian influenza A(H10N3) | China | June 10 |
| Monkeypox | United Kingdom of Great Britain and Northern Ireland | June 11 |
| Monkeypox | Texas, United States of America | July 27 |
| Marburg virus disease | Guinea | August 9 |
| Human infection with avian influenza A(H5N1) | India (Haryana state) | August 16 |
| MERS-CoV virus disease | Saudi Arabia | August 17 |
| Meningococcal meningitis | Democratic Republic of the Congo | September 20 |
| Nipah virus disease | India (Kerala state) | September 24 |
| Plague | Madagascar | October 1 |
| Yellow Fever | Nigeria | October 1 |
| Ebola virus disease | Democratic Republic of the Congo | October 10 |
| Yellow Fever | Venezuela (Bolivarian Republic of) | October 13 |
| Zika virus disease | India | October 14 |
| Monkeypox | United States of America (Washington D.C) | November 25 |
| Yellow Fever | Ghana | December 1 |
| MERS-CoV virus disease | United Arab Emirates | December 13 |
| Dengue Fever | Pakistan | December 14 |
| Cholera | Cameroon | December 16 |
| Ebola virus disease | Democratic Republic of the Congo | December 16 |
Diseases in Table 1 are not epidemics, but they have the potential to spread across the world, especially following wars, internal disturbances, earthquakes, floods, and even due to urbanization and climate change. Infectious diseases might spread to more countries as a result of human mobility and migration movements due to commercial activities and tourism.
Control, elimination, and eradication programs continue regarding diseases of concern and potential outbreaks. There are vaccine-preventable disease control programs, such as poliomyelitis eradication programs, measles and rubella, maternal and neonatal tetanus elimination programs, hepatitis A and hepatitis B control programs, and diphtheria and tuberculosis control programs. Moreover, there are vector-borne disease control programs, such as malaria, oriental sore, and Crimean-congo hemorrhagic fever control programs. The most important programs to fight infectious diseases include monitoring bird flu which might lead to epidemics, zika, and global threats like hand-foot-and-mouth disease, and control activities for HIV/AIDS.
Despite all these efforts, international solidarity against epidemics that might lead to pandemics is not quite enough. The last example is the still active COVID-19 pandemic, which started in Wuhan, China on December 2019. All countries of the world experienced a pandemic with the outbreak and spread of a virus called SARS-CoV-2 and tried to prevent its spread by non-medical protection measures including personal measures (mask, distancing and hygiene rules, avoiding crowded places), and measures taken by governments to reduce social activities (curfews, closing of workplaces, interruption of education, flexible work models).
Governments have started immunizing their people with vaccines after receiving emergency use authorization with the results from research studies of some vaccines until the end of 2020. The number of COVID-19-related cases has reached 274,633,041, and the reported number of deaths has reached 5,368,732. It is estimated that 70-85 million people died during World War II in the 20th century, which makes the COVID-19 pandemic the second biggest tragedy after the Second World War.
When SARS-CoV-2 is analyzed in terms of its viral load and recovery process, it can be seen that the virus stays in the upper respiratory tract for 17 days, in the lower respiratory tract for 14.6 days, in the stool for 17.2 days, and in serum samples for 16.6 days on average. However, it is highlighted that generally, virus release stops as of the ninth day except for immunosuppressive patients.
Case numbers increasing with the arrival of winter in the northern hemisphere demonstrates that SARS-CoV-2 is linked with seasonal conditions. The stability of viruses increases, and the natural immune response of people decreases in dry and cold winter weather. Gathering indoors on autumn and winter days and mutations pave the way for viruses to spread rapidly. As the Coronavirus is an RNA virus, multiple mutations emerged and some of which have spread around the world like a new pandemic. UK-based Alpha, India-based Delta-Delta plus, and lastly South Africa-based Omicron variants were dominant variants of the virus. Compared to the virus seen in Wuhan, these variants are respectively 2-3 times more contagious. It is highlighted that the Alpha variant is 3-5 times more contagious than the Wuhan virus, the Delta variant is 3-6 times more contagious than the Alpha variant, and the Omicron variant is 3-5 more contagious than the Delta variant.
See Diagram 1 for the impact of new variants seen in Türkiye on the number of cases. 60,000 daily cases for the Alpha variant in April 2021, and 6,000 daily cases for Delta-Delta Plus reached 20-30 thousand despite vaccination, and the number of deaths reached 180-280. Omicron is still active in Türkiye and causes the number of cases to increase.
Non-medical measures were taken to prevent the spread of the virus and reduce the disease burden in Türkiye in 2021. It was an unstable year with decreases in the number of cases when restrictions were imposed and increases when restrictions were lifted. There were many opinions stating that these restrictions led to increases in mental health problems in society and domestic violence against women and children, setbacks in monitoring individuals with chronic diseases, and problems in the economy.
Türkiye turned to inactive vaccinations as of January 2021, and mRNA vaccinations began as of May 2021. 123,625,349 doses of vaccines were administrated as of 19 December 2021, 56,649,405 of those being the first dose, and 51,142,896 of them the second dose. The third dose, also called the booster dose, was administrated to 13,912,051 people. The speed of vaccinations for two doses is estimated to be 82.39% for adults aged 18 and over.
Significant studies were carried out on virologic, immunologic, epidemiologic, clinic properties, treatments, non-medical protection measures, newly developed vaccines, and pharmaceuticals. According to Pubmed, Google Scholar and Google search engine results on 18 December 2021, the number of scientific publications was 205,511 on Pubmed, and 221,000 on Google Scholar, and when the keyword “COVID-19” was searched on Google search engine, there were 4,710,000 titles.
It is still so important to take measures and increase vaccination rates all over the world. Governments know that it is impossible to eliminate the pandemic by just taking measures within their territories. Therefore, we have to support the immunization processes of countries with a supply shortage in vaccination.
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