The first stage of the demographic transition model includes high birth rates and high death rates – and infectious diseases dominate – for example, the black death was a highly infectious disease that killed millions in Europe – if memory serves, 60% of Venice died, and about a third of Italy’s population. The 90% fatalities in Constantinople suggests that it was worse in cities. A time of a life expectancy of around 30 years, because so many died young. I’m not certain how effective the masks of the time were in combating the disease transmission.
The second stage includes infectious diseases – such as cholera – that could be controlled by sanitation. Models don’t always fit as well as we would like – at the same time that public health and improved sanitation was getting a handle on cholera, smallpox vaccination was becoming a norm. It was 1832 when Congress passed the Indian Vaccination Act, ordering the army to vaccinate the Indians. Typhoid Mary remains in our vocabulary, a woman who showed no outward sign of infection, but spread typhoid wherever she cooked. In her case, she was basically incarcerated because of her infection (and she kept escaping). Stage 2 of the demographic transition is characterized by fewer pandemics, and life expectancy may rise as high as 50 years. Our masking, quarantines and isolation are public health techniques developed in the second stage of demographic transition. John Snow’s removal of the Broad Street pump handle was very effective at reducing the waterborne cholera transmission.
The third Stage is the stage of degenerative and man-made diseases – picture how cigarettes fit in with lung cancer and heart disease. Just living longer increases your chances of dying from a degenerative disease. Infant mortality drops, and life expectancy is pretty much in the mid-fifties. The public health approach here is to change unhealthy behaviors like smoking while relying on medical research to counteract degenerative diseases. The term “safe sex” comes from a public health program to reduce AIDS (HIV). When it works, and it has, we move into the fourth stage of demographic transition.
Stage 4 – where we are in the US today – shows an increase in degenerative diseases, better medical care, and a life expectancy that exceeds 70 years.
It is no wonder that Covid took everyone by surprise – in Stage 4, we’re used to having pandemics under some form of control – our top 3 causes of death are heart disease, cancer and accidents. The Corona virus came in with an approach that complemented our stage in the demographic transition model – a pandemic that killed in a relationship to the age of the infected. Probably the first clue was the word “comorbidity” becoming so much of the vocabulary. This time we hit a pandemic that worked in combination with the degenerative diseases. A disease that matches an aging population. A disease that needed a stage 4 response. Lacking that stage 4 response, we’ve spent the year responding as we did to diseases during the second stage of demographic transition.
Another Stage 4 pandemic will develop – after all, we have a stage 4 population as an incubator. We may even develop new strategies for dealing with it.