eesti teaduste
akadeemia kirjastus
SINCE 1952
Proceeding cover
of the estonian academy of sciences
ISSN 1736-7530 (Electronic)
ISSN 1736-6046 (Print)
Impact Factor (2020): 1.045

The Estonian H1N1 influenza 2009 outbreak was highly underestimated; pp. 320–329

Full article in PDF format | doi: 10.3176/proc.2012.4.07

Regina Saar, Diivi Põdersoo, Mari Järvelaid, Linda Tuubel, Jaanus Suurväli, Anu Nutt, Merle Saaremäe, Tiiu Saar, Sirje Rüütel Boudinot


The H1N1 influenza strain Mexico 2009 (H1N1pandemic09) led to mild symptoms (with no or low fever) in Estonia during the 2009–2010 outbreak. Due to the lack of clinical signs, it was difficult to estimate the real spreading of this influenza virus in Estonia and no cases of H1N1 influenza were officially registered in animals either. We used an ELISA method to screen blood sample collections for the presence of anti-H1N1 and anti-H3N2 antibodies. All sera were also tested with the hemagglutination inhibition (HI) assay. Out of the 123 samples from human patients, 23 (i.e. 18.7%) were seropositive for the H1N1pandemic09 virus. In addition, blood samples from six persons were positive for both H1N1 and H3N2 viruses, while according to the data from the Estonian Health Board, people aged 15–65 had a general disease rate of around 3.9%. Almost all of the tested animals from two herds (out of four studied) were seropositive for H1N1pandemic09. The seven HA protein sequences isolated from Estonia were aligned with a consensus sequence of the pandemic H1N1 HA sequences from Mexico using ClustalW, and 12 amino acids substitutions were found.



  1. Pandemic (H1N1) 2009 virus; Pandemic H1N1/09 virus, (H1N1pandemic09). swineflu/frequently_asked_questions/about_disease/en/index.html (visited 07.07.2011).

  2. Simonsen, L., Clarke, M. J., Schonberger, L. B., Arden, N. H., Cox, N. J., and Fukuda, K. Pandemic versus epidemic influenza mortality: a pattern of changing age distribution. J. Infect. Dis., 1998, 178(1), 53–60.

  3. Reed, C., Angulo, F. J., Swerdlow, D. L. et al. Estimates of the prevalence of pandemic (H1N1) 2009, United States, April–July 2009. Emerg. Infect. Dis., 2009, 15(12), 2004–2007.

  4. Khandaker, G., Dierig, A., Rashid, H., King, C., Heron, L., and Booy, R. Systematic review of clinical and epidemiological features of the pandemic influenza A (H1N1) 2009. Influenza Other Respi. Viruses, 2011, 5(3), 148–156.

  5. Anonymous. swineflu/clinical_management/en/ (visited 07.07.2011).

  6. Shinde, V., Bridges, C. B., Uyeki, T. M. et al. Triple-reassortant swine influenza A (H1) in humans in the United States, 2005–2009. N. Engl. J. Med., 2009, 360, 2616–2625.

  7. Miller, D. R., Christie, G. L., Molyneaux, P., and Currie, G. P. An outbreak of H1N1 influenza in a respiratory unit. Thorax, 2010, 65(10), 938–939.

  8. Coudeville, L., Andre, P., Bailleux, F., Weber, F., and Plotkin, S. A new approach to estimate vaccine efficacy based on immunogenicity data applied to influenza vaccines administered by the intradermal or intramuscular routes. Hum. Vaccin., 2010, 6(10), 841–848.

  9. Stittelaar, K. J., Veldhuis Kroeze, E. J., Rudenko, L. et al. Efficacy of live attenuated vaccines against 2009 pandemic H1N1 influenza in ferrets. Vaccine, 2011, 29(49), 9265–9270.

10. Estonian Health Board website on the new infuenza virus A (H1N1). nakkushaigused/gripi-info.html (visited 07.07.2011).

11. Palmer, D. F., Dowdle, W. R., Coleman, M. T., and Schild, G. C. Advanced Laboratory Techniques for Influenza Diagnosis. U.S. Department of Health, Education, and Welfare, Immunology Series, No. 6. Centers for Disease Control and Prevention, Atlanta, GA, 1975.

12. CIDRAP Influenza Overview. cidrap/content/influenza/swineflu/biofacts/swinefluoverview.html (visited 07.07.2011).

13. Hofshagen, M., Gjerset, B., Er, C. et al. Pandemic influenza A(H1N1)v: human to pig transmission in Norway? Euro Surveill., 2009, 14(45), pii: 19406.

14. Chenna, R., Sugawara, H., Koike, T. et al. Multiple sequence alignment with the Clustal series of programs. Nucleic Acids Res., 2003, 31(13), 3497–3500.

15. Zhao, R., Cui, S., Guo, L. et al. Identification of a highly conserved H1 subtype-specific epitope with diagnostic potential in the hemagglutinin protein of influenza A virus. PLoS ONE, 2011, 6(8), 1–10.

16. Strengell, M., Ikonen, N., Ziegler, T., and Julkunen, I. Minor changes in the hemagglutinin of influenza A(H1N1)2009 virus alter its antigenic properties. PLoS ONE, 2011, 6(10), e25848.

17. Kilbourne, E. D. Influenza pandemics of the 20th century. Emerg. Infect. Dis., 2006, 12(1), 9–14.

18. Communicable Disease Statistics in Estonia. Part 4. Health Protection Inspectorate, 1998, 70.

19. Aaver, E. Etiology of swine influenza and concepts of fight with it in Estonia. Ministry of Agriculture of Estonia, 1957 (in Russian).

20. Hjulsager, C. K., Breum, S. Ø., Nielsen, L. P., Treb­bien, R., and Larsen, L. E. Pandemic influenza a h1n1v circulates in Danish pigs. 2011.; o.28 (visited 14.11.2011).

21. Grøntvedt, C. A., Er, C., Gjerset, B. et al. Pandemic influenza virus outbreak in Norway 2009∕10: a case-control study in swine nucleus and multiplier herds preliminary findings. 2011. http://www.emerging2011. com/multisites/pig2011/templates/yoo_nu/images/site/pdf/Proceedings.pdf; o.29 (visited 14.11.2011).

22. Gjerset, B., Germundsson, A., Er, C., Jørgensen, A., and Lium, B. Screening for pandemic influenza h1n1 in the Norwegian pig population in 2010. 2011.; p.178 (visited 14.11.2011).

23. Markowska-Daniel, I., Kowalczyk, A., and Pejsak, Z. Prevalence of H1N1, H1N2 and H3N2 swine influenza virus in Polish herds in 2010 comparing to the period 1998–2009. 2011. multisites/pig2011/templates/yoo_nu/images/site/pdf/Proceedings.pdf; p.188 (visited 11.11.2011).

24. Simon, G., Hervé, S., Rose, N., and Marchal, C. Trans­mission of pandemic influenza A/H1N1 2009 virus to pigs in New Caledonia, an insular region previously free from swine influenza viruses. 2011.; p.191 (visited 11.11.2011).

25. Medina, R. A., Manicassamy, B., Stertz, S. et al. Pandemic 2009 H1N1 vaccine protects against 1918 Spanish influenza virus. Nat. Commun., 2010, 1(3), 1–6.

26. Jones, D. T., Taylor, W. R., and Thornton, J. M. The rapid generation of mutation data matrices from protein sequences. Computer Appl. Biosci., 1992, 8, 275–282.

27. Felsenstein, J. Confidence limits on phylogenies: an approach using the bootstrap. Evolution, 1985, 39, 783–791.

28. Tamura, K., Peterson, D., Peterson, N., Stecher, G., Nei, M., and Kumar, S. MEGA5: Molecular evolu­tionary genetics analysis using Maximum Likelihood, Evolutionary Distance, and Maximum Parsimony methods. Mol. Biol. Evol., 2011, 28, 2731–2739.


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