Intended for healthcare professionals

CCBYNC Open access

Partial protection of seasonal trivalent inactivated vaccine against novel pandemic influenza A/H1N1 2009: case-control study in Mexico City

BMJ 2009; 339 doi: (Published 06 October 2009) Cite this as: BMJ 2009;339:b3928
  1. Lourdes Garcia-Garcia, research professor1,
  2. Jose Luis Valdespino-Gómez, epidemiologist2,
  3. Eduardo Lazcano-Ponce, research professor1,
  4. Aida Jimenez-Corona, research professor1,
  5. Anjarath Higuera-Iglesias, epidemiologist3,
  6. Pablo Cruz-Hervert, research professor1,
  7. Bulmaro Cano-Arellano, engineer1,
  8. Antonio Garcia-Anaya, engineer1,
  9. Elizabeth Ferreira-Guerrero, epidemiologist1,
  10. Renata Baez-Saldaña, research professor1,
  11. Leticia Ferreyra-Reyes, research professor1,
  12. Samuel Ponce-de-León-Rosales, infectious diseases specialist2,
  13. Celia Alpuche-Aranda, infectious diseases specialist4,
  14. Mario Henry Rodriguez-López, research professor1,
  15. Rogelio Perez-Padilla, research professor3,
  16. Mauricio Hernandez-Avila, epidemiologist5
  1. 1Instituto Nacional de Salud Pública, Cuernavaca, Mor, Mexico
  2. 2Laboratorios de Biológicos y Reactivos de México (BIRMEX), Amores 1240, Col Del Valle, Delegación Benito Juárez. CP 03100, Distrito Federal, Mexico
  3. 3Instituto Nacional de Enfermedades Respiratorias (INER), Distrito Federal, México
  4. 4Instituto de Diagnóstico y Referencia Epidemiológicos (InDRE), Distrito Federal, Mexico
  5. 5Subsecretariat of Health Prevention and Promotion, Distrito Federal, Mexico
  1. Correspondence to: J L Valdespino jvaldespinog{at}
  • Accepted 18 September 2009


Objective To evaluate the association of 2008-9 seasonal trivalent inactivated vaccine with cases of influenza A/H1N1 during the epidemic in Mexico.

Design Frequency matched case-control study.

Setting Specialty hospital in Mexico City, March to May 2009.

Participants 60 patients with laboratory confirmed influenza A/H1N1 and 180 controls with other diseases (not influenza-like illness or pneumonia) living in Mexico City or the State of Mexico and matched for age and socioeconomic status.

Main outcome measures Odds ratio and effectiveness of trivalent inactivated vaccine against influenza A/H1N1.

Results Cases were more likely than controls to be admitted to hospital, undergo invasive mechanical ventilation, and die. Controls were more likely than cases to have chronic conditions that conferred a higher risk of influenza related complications. In the multivariate model, influenza A/H1N1 was independently associated with trivalent inactivated vaccine (odds ratio 0.27, 95% confidence interval 0.11 to 0.66) and underlying conditions (0.15, 0.08 to 0.30). Vaccine effectiveness was 73% (95% confidence interval 34% to 89%). None of the eight vaccinated cases died.

Conclusions Preliminary evidence suggests some protection from the 2008-9 trivalent inactivated vaccine against pandemic influenza A/H1N1 2009, particularly severe forms of the disease, diagnosed in a specialty hospital during the influenza epidemic in Mexico City.


  • We thank the patients and healthcare workers of the National Institute of Respiratory Diseases for their generous support and cooperation.

  • Contributors: LG-G, JLV-G, and EL-P participated in the study design, data management, and data analysis, and wrote the manuscript. AJ-C, PC-H, AG-A, and BC-A participated in the study design and contributed to the analyses. AH-I, EF-G, RB-S, LF-R, SPdeLR, and CA-A contributed to the design and implementation of the study. MHR-L, RP-P, and MH-A made valuable contributions to the study’s design, analysis, and writing of the manuscript. All authors reviewed and approved the final manuscript, had full access to all of the data (including statistical reports and tables) in the study, and can take responsibility for the integrity of the data and the accuracy of the data analysis. LG-G and JLV-G are the guarantors.

  • Funding: This study was supported by the Mexican Ministry of Health. The funding source did not influence or participate in the design and conduct of the study; in the collection, management, analysis, and interpretation of the data; in writing the manuscript; or in the decision to submit the article for publication. The researchers were independent of the funder.

  • Competing interests: JLV-G and SPdeLR are employed by Laboratorios de Biológicos y Reactivos de México (BIRMEX).

  • Ethical approval: This study was approved by the appropriate institutional review boards.

  • Data sharing: The technical appendix, statistical code, and dataset are available from

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-commercial License, which permits use, distribution, and reproduction in any medium, provided the original work is properly cited, the use is non commercial and is otherwise in compliance with the license. See: and

View Full Text