Safety from infectious diseases depends on antibiotics and vaccines

Igor Rudan is a well-known Croatian scientist, a member of the Royal Society of Edinburgh and the author of numerous popular scientific articles and books "The exact color of the sky" and "The evil air" in which he describes the development of science and the areas he deals with - medicine and molecular biology - in an accessible way. In the column he writes for Zagreb Vecernji list this time he wrote about the history of infectious diseases and threats for which humans have no solution. He considers the fact that more and more people are beginning to doubt the importance and safety of vaccines to be unbelievable. Rudan's latest column is transmitted in its entirety.

"In 1914, the First World War broke out. If we recall the four horsemen of the Apocalypse, this was a horseman of "war" like no other before him. He claimed as many as 17 million lives, left behind another 20 million wounded, and led to mass destruction and countless of human tragedy and suffering. But things would soon become much worse. The war created the perfect conditions for the flu to strike again. This time, the Spanish flu spread rapidly through the exhausted, malnourished, displaced, and depressed human population after the end of the war, killing more out of 75 million people.It's probably the worst case of a "double whammy" we've experienced as a human species - and it hit us just a hundred years ago.

Pandemic flu keeps coming back, in cycles every ten to 30 years, because the virus is constantly mutating and changing in wild waterfowl and ducks and then finding a way to "jump" to humans. Pigs can also be infected with both human and bird strains, which can lead to the mixing of genetic material of different influenza viruses, as well as the creation of new viruses. The Asian flu pandemic of 1957 killed two million people, and the Hong Kong flu pandemic of 1968 left another million dead.

Along with bubonic plague, cholera, leprosy and flu, it is clear that other epidemic diseases historically brought mass plague to our ancestors, and above all smallpox, measles and typhus. Smallpox has probably killed more than a billion people throughout recorded history. It was a very contagious disease, caused by the smallpox virus, and it is also remembered as the first disease that people managed to completely eradicate from the planet by vaccination. Considering the total number of lives that have since been saved by preventing the occurrence of that disease, as well as saving treatment costs, the eradication (extermination) of smallpox and vaccination against smallpox may be the greatest success of us as a human species so far, at least in public health. Smallpox significantly contributed to the destruction of Central and South American civilizations and caused hundreds of millions of deaths throughout human history.

Typhus is sometimes called “camp fever” because it usually strikes as an epidemic during armed conflicts. It was first described during the Crusades, and it remained a prominent cause of death in many subsequent wars. In the period between the 16th and 20th centuries, it is thought that more soldiers died from typhus than from military operations. In the 21st century, we are beginning to forget about our catastrophic collective past and the unimaginable death tolls that infectious diseases inflicted on our ancestors. We are among the first generations of people who are no longer afraid of infectious diseases.

Thanks to antibiotics and vaccines, which now protect us, the human population has increased from about 1,5 billion at the beginning of the 20th century to 7,5 billion at the beginning of the 21st century. That's five times more people on Earth, and that's mostly because we've learned how to prevent and treat the most dangerous infections. But how sure are we really? Microbes are incredibly numerous in nature and have very short life cycles. That is why they can adapt very quickly to threats to their survival, such as antibiotics, through mutations. The massive and excessive use of antibiotics – not only to protect humans but also animals in livestock – puts us all at risk. It allows microorganisms to adapt and develop resistance to antibiotics, which precipitates new future epidemics with new, resistant bacteria.

With antibiotic resistance, it is almost unbelievable that more and more people are beginning to doubt the importance and safety of vaccines, leading to reduced vaccination of the population and the loss of our "collective immunity". Herd immunity also protects those who remain unvaccinated, for example babies who are too young to respond to vaccines with an immune response. There is also a theoretical danger of a phenomenon called "serotype switching". Such a problem can arise when in nature there are various strains (so-called serotypes) of specific bacteria or viruses that compete against each other. If we use vaccines to prevent infections with the most prevalent strains, then those strains will disappear very quickly, but will soon be replaced by some other strain. These new strains are not currently included in vaccines, so they may lead to even more severe forms of the disease. It is obvious that our apparent safety from infectious diseases is highly dependent on antibiotics and vaccines. That is why investments in improving existing and adding new vaccines and antibiotics should continue, as well as ensure that the safety standards in their production and application are very high. Of increasing concern is our recently acquired ability to manipulate the genetic codes of bacteria and viruses.

Understanding what makes them infectious and deadly could theoretically lead to the development of genetically modified strains that could wipe out our entire species. Historically, there are examples of the use of anthrax, smallpox, plague and cholera as weapons in the so-called biological warfare. We can only hope that such an idea will not be considered in modern times. Our current level of technology could lead to artificially engineered and genetically engineered strains that could cause far more deaths than any other weapon. Although in the 21st century we feel safer from infectious diseases, we have already witnessed a number of serious dangers. First, in 2002, more than 750 deaths were caused by SARS - severe acute respiratory syndrome - a new, atypical pneumonia caused by the coronavirus.

A quick response by public health services helped to stop the spread then, but the disease is by no means eradicated and could re-emerge and turn into a pandemic. Then in 2009, a new flu pandemic broke out. It caused great concern because the antigenic signature of the virus - H1N1 - was the same as that of the disastrous "Spanish flu" of 1918. Fortunately, this new strain of the H1N1 virus was created by mixing avian, swine and human flu viruses, which led to to the common popular name for this pandemic - swine flu. The pandemic caused about 15.000 deaths worldwide. In 2012, MERS - Middle East Respiratory Syndrome - broke out, with cases reported in more than 20 countries. The disease was caused by a new variant of the coronavirus. MERS has caused more than 800 deaths in Middle Eastern countries and remains a threat, but after SARS and MERS, this seventh coronavirus - SARS-CoV-2 - has caused a true pandemic of the disease, COVID-19, and much greater problems for humanity, although it had a significantly lower death rate than its two predecessors. In doing so, it showed that the ability and speed of the virus to spread among humans posed a greater problem to epidemiologists than the death rate among those infected."