Seasonal Flu Vaccine May Lessen Swine Flu Impact
But it won't fully protect people from the H1N1 virus, experts say
By Steven Reinberg, HealthDay Reporter
TUESDAY, Oct. 6 (HealthDay News) -- The seasonal flu vaccine may offer partial protection against the pandemic H1N1 swine flu, but not enough to prevent a person from catching the swine flu, Mexican researchers say.
In a study of hospital patients during the H1N1 epidemic in Mexico City last spring, the researchers found that those who had had a seasonal flu shot and were infected with the H1N1 flu had significantly milder cases than those who had not received a seasonal flu shot.
For the study, a group led by Dr. Jose Luis Valdespino-Gomez reviewed the outcomes of 60 patients with swine flu and 180 patients with other diseases. Some of the patients reported having received a 2008-09 seasonal flu shot.
"Seasonal vaccine may provide partial protection against pandemic influenza, particularly severe forms of the disease," said Valdespino-Gomez, an epidemiologist at Laboratorios de Biologicos y Reactivos de Mexico.
But Valdespino-Gomez cautioned that these findings do not mean that a seasonal flu shot will fully protect you from the H1N1 swine flu or its complications. "These results do not mean that people should not be vaccinated with the H1N1 influenza vaccine," he said. "The recommendation is to receive both seasonal and H1N1 vaccines."
This year's seasonal flu vaccine is available now, and the new H1N1 vaccine is about to be distributed. People should get both shots, according to the U.S. Centers for Disease Control and Prevention.
The seasonal vaccine may boost existing antibodies in those who have had a similar flu virus or a vaccination against seasonal flu, the researchers say.
The study, published in the Oct. 7 online edition of the British Medical Journal, has limitations because of the small number of participants. "In addition, the control group had a high frequency of chronic underlying conditions and a high frequency of seasonal vaccination, which may underestimate our results," Valdespino-Gomez said.
Dr. Marc Siegel, an associate professor of medicine at New York University School of Medicine in New York City, isn't surprised to hear that a seasonal flu shot offers some protection from the swine flu.
"The implication is that if you trigger an antibody response to an H1N1 flu virus of any kind, it may be useful as part of the body's attempt to fight the flu," he said. "That would explain why it wouldn't immunize you, but could prevent you from having a severe outcome."
Siegel cautioned that the seasonal vaccine the study participants received was last year's vaccine. This year's seasonal vaccine is a different mix of viruses so it may not have any protection against the H1N1 swine flu, he said.
"People who have gotten a seasonal flu shot should not assume they are protected from the H1N1 flu," Siegel said. "Clearly, the amount of protection you are getting from a seasonal flu shot is not nearly of the magnitude that would take the place of getting this year's H1N1 vaccine."
You need both shots, he said.
For more information on flu, visit the Flu.gov.
SOURCES: Jose Luis Valdespino-Gomez, M.D., M.P.H., epidemiologist, Laboratorios de Biologicos y Reactivos de Mexico, Mexico City; Marc Siegel, M.D., associate professor, medicine, New York University School of Medicine, New York City, and author, Swine Flu: The New Pandemic; Oct. 7, 2009, British Medical Journal, online
Copyright (c) 2009 ScoutNews, LLC. All rights reserved.
Published 6 October 2009, doi:10.1136/bmj.b3928
Cite this as: BMJ 2009;339:b3928
Partial protection of seasonal trivalent inactivated vaccine against novel pandemic influenza A/H1N1 2009: case-control study in Mexico City
Lourdes Garcia-Garcia, research professor1, Jose Luis Valdespino-Go'mez, epidemiologist2, Eduardo Lazcano-Ponce, research professor1, Aida Jimenez-Corona, research professor1, Anjarath Higuera-Iglesias, epidemiologist3, Pablo Cruz-Hervert, research professor1, Bulmaro Cano-Arellano, engineer1, Antonio Garcia-Anaya, engineer1, Elizabeth Ferreira-Guerrero, epidemiologist1, Renata Baez-Saldan~a, research professor1, Leticia Ferreyra-Reyes, research professor1, Samuel Ponce-de-Leo'n-Rosales, infectious diseases specialist2, Celia Alpuche-Aranda, infectious diseases specialist4, Mario Henry Rodriguez-Lo'pez, research professor1, Rogelio Perez-Padilla, research professor3, Mauricio Hernandez-Avila, epidemiologist5
1 Instituto Nacional de Salud Pu'blica, Cuernavaca, Mor, Mexico, 2 Laboratorios de Biolo'gicos y Reactivos de Me'xico (BIRMEX), Amores 1240, Col Del Valle, Delegacio'n Benito Jua'rez. CP 03100, Distrito Federal, Mexico, 3 Instituto Nacional de Enfermedades Respiratorias (INER), Distrito Federal, Me'xico, 4 Instituto de Diagno'stico y Referencia Epidemiolo'gicos (InDRE), Distrito Federal, Mexico, 5 Subsecretariat of Health Prevention and Promotion, Distrito Federal, Mexico
Correspondence to: J L Valdespino email@example.com
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.
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: http://creativecommons.org/licenses/by-nc/2.0/ and http://creativecommons.org/licenses/by-nc/2.0/legalcode.
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