Importancia de la viruela, gastroenteritis aguda y paludismo ... - Oulu

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6.3 Smallpox
− Smallpox was endemic in Finland at the beginning of the period under study: there
were cases in every region of the country, mainly among small children.
− Even in a general context of endemicity, the disease underwent cyclic peaks and
troughs with a periodicity varying between 5 and 7 years. Within one year, the
maximum mortality was generally reached in spring. Both periodicity and seasonality
seemed to obey more the internal dynamics of the disease than either the birth rate or
external factors influencing the population.
− During peak years, smallpox could cause between one tenth and one quarter of all the
deaths of the country. The figure could even reach beyond one half at local level in
some specific regions.
− The disease caused a greater number of deaths in the more populated areas, but
relatively speaking, it was a more important cause of death in the southeast of the
country.
− The southeastern regions of Finland could have been acting as reservoirs for the
disease during the period under study. The number of cases in that area show a less
defined seasonality and smaller differences among epidemic peaks and troughs.
− During every peak, which usually lasted 2-5 years, the disease moved across the
country, not always following the same path, but anyway according to certain patterns:
many episodes started in the southeast and crossed the country, causing great deaths
numbers sometimes in Ostrobothnia, sometimes in the northeast of the country.
− Along the period under study, it can be observed a gradual decrease in the importance
of smallpox as a cause of death. The spread of vaccination and an improvement of the
systems of early case detection and isolation are, beyond doubt, some of the most
important explanations of this trend, but they are not the only ones. The downwards
trend is clear from the last decade of the 18th century while vaccination does not reach
Finland until 1802 and it takes some decades before it becomes widespread.
− Three non-excluding hypotheses are perhaps the most plausible explanations for the
phenomenon:
− Inoculation, practiced mainly in Ostrobothnia during the last decades of the 18th
century, may have been more extensive and more effective than it has been
historically considered.
− A common disease with a relatively high case-fatality rate as smallpox could have
exerted a selective pressure on the population.
− There may have been decrease in the virulence of the virus.
It is difficult to evaluate the validity and weight of these hypotheses, but probably these
factors combined with vaccination and other preventive measures resulted in the
reduction of annual smallpox deaths to less than 2% by 1850.