Predicting AH1N1 2009 influenza epidemic in Southeast Europe

To use the data on the AH1N1 2009 influenza epidemic in the Southern hemisphere countries to predict the course and size of the upcoming influenza epidemic in South-Eastern Europe (SEE) countries and other regions of the World with temperate climate.

We used a comparative epidemiological method to evaluate accessible electronic data on laboratory-confirmed deaths from AH1N1 2009 influenza in the seasons 2009/2010 and 2010/2011. The studied SEE countries were Albania, Bosnia and Herzegovina, Bulgaria, Croatia, Greece, Hungary, Kosovo, Macedonia, Montenegro, Romania, Serbia, and Slovenia, while Southern hemisphere countries were Argentina, Australia, Chile, New Zealand, Paraguay, Uruguay, and South Africa.

In influenza season 2009/2010, Southern hemisphere countries with temperate climate reported 1187 laboratory-confirmed influenza AH1N1 2009 deaths (mortality rate 0.84/100000; 95% confidence interval [CI], 0.50-1.24). SEE countries with similar climatic conditions reported 659 deaths and similar mortality rates (0.86/100000, 95% CI, 0.83-1.10). In the whole Europe without the Commonwealth of Independent States countries (CIS, former Soviet Union), there were 3213 deaths (0.60/100000; 95% CI, 0.65-0.93). In 2010/2011, Southern hemisphere countries reported 94 laboratory-confirmed deaths (mortality rate 0.07/100000; 95% CI, 0.02-0.28) or only 7.9% of the previous season. SEE countries by the end of the 11th epidemiological week of 2010/2011 season reported 489 laboratory-confirmed deaths, with a mortality rate of 0.64/100000 (95% CI, 0.26-0.96) or 74.2% of the previous season, which was significantly higher than in the Southern hemisphere countries (χ(2) (1) =609.1, P<0.001). In Europe without CIS countries, there were 1836 deaths, with a mortality rate of 0.34/100000 (χ(2) =153.3, P<0.001 vs SEE countries).

In the 2009/2010 season, SEE countries and Southern hemisphere countries had similar influenza AH1N1 2009 mortality rates. In the 2010/2011 season, the forecast of 10% increase in total mortality in SEE countries and Europe compared with the 2009/2010 season was significantly exceeded, while the expected impact of type-specific vaccines against influenza AH1N1 2009 was not achieved. Consumption of epidemic potential has greater importance for the prognosis of the course and size of influenza epidemic than the degree of vaccine immunity.