Prior Infections With Seasonal Influenza A/H1N1 Virus Reduced the Illness Severity and Epidemic Intensity of Pandemic H1N1 Influenza in Healthy Adults

[tetano]

Oxford Journals
Medicine
Clinical Infectious Diseases
Advance Access
10.1093/cid/cir809


Prior Infections With Seasonal Influenza A/H1N1 Virus Reduced the Illness Severity and Epidemic Intensity of Pandemic H1N1 Influenza in Healthy Adults

Robert B. Couch1,2,
Robert L. Atmar1,2,
Luis M. Franco2,3,
John M. Quarles6,
Diane Ni?o1,
Janet M. Wells1,
Nancy Arden6,
Sheree Cheung1, and
John W. Belmont3,4,5

+ Author Affiliations

1Department of Molecular Virology and Microbiology
2Department of Medicine
3Department of Molecular and Human Genetics
4Department of Pediatrics
5Department of Pathology and Immunology, Baylor College of Medicine, Houston, Texas
6College of Medicine, Texas A&M Health Science Center, College Station

Correspondence: Robert B. Couch, MD, Department of Molecular Virology and Microbiology, Baylor College of Medicine, One Baylor Plaza, MS: BCM280, Houston, TX 77030 (ikirk@bcm.edu).

Abstract

Background. A new influenza A/H1N1 (pH1N1) virus emerged in April 2009, proceeded to spread worldwide, and was designated as an influenza pandemic. A/H1N1 viruses had circulated in 1918?1957 and 1977?2009 and were in the annual vaccine during 1977?2009.

Methods. Serum antibody to the pH1N1 and seasonal A/H1N1 viruses was measured in 579 healthy adults at enrollment (fall 2009) and after surveillance for illness (spring 2010). Subjects reporting with moderate to severe acute respiratory illness had illness and virus quantitation for 1 week; evaluations for missed illnesses were conducted over holiday periods and at the spring 2010 visit.

Results. After excluding 66 subjects who received pH1N1 vaccine, 513 remained. Seventy-seven had reported with moderate to severe illnesses; 31 were infected with pH1N1 virus, and 30 with a rhinovirus. Determining etiology from clinical findings was not possible, but fever and prominent myalgias favored influenza and prominent rhinorrhea favored rhinovirus. Tests of fall and spring antibody indicated pH1N1 infection of 23% had occurred, with the rate decreasing with increasing anti-pH1N1 antibody; a similar pattern was seen for influenza-associated illness. A reducing frequency of pH1N1 infections was also seen with increasing antibody to the recent seasonal A/H1N1 virus (A/Brisbane/59/07). Preexisting antibody to pH1N1 virus, responses to a single vaccine dose, a low infection-to-illness ratio, and a short duration of illness and virus shedding among those with influenza indicated presence of considerable preexisting immunity to pH1N1 in the population.


Conclusions. The 2009 A/H1N1 epidemic among healthy adults was relatively mild, most likely because of immunity from prior infections with A/H1N1 viruses.

http://cid.oxfordjournals.org/content/early/2011/11/10/cid.cir809.short

 

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Re: Prior Infections With Seasonal Influenza A/H1N1 Virus Reduced the Illness Severity and Epidemic Intensity of Pandemic H1N1 Influenza in Healthy Adults

Past flu exposures weakened pandemic severity

NEW YORK (Reuters Health) - Immunity gained by coming down with a previous, seasonal version of the flu helped temper the severity of the pandemic flu that spread around the globe in 2009, according to a new study.

Texas researchers monitored hundreds of adults throughout the 2009-2010 flu season, and found that those who had had seasonal flu in the past were less likely to catch the pandemic strain, and less likely to be severely ill if they did, than people whose immune systems had not been exposed to earlier flu viruses.

People's immune systems remember past encounters with a particular virus and that primes them to ward it off in the future. In the case of the pandemic of 2009, the influenza virus happened to be from the same family of flu strains, known as H1N1, as prior seasonal flus.

"They're both called H1 for a reason," said Mark Lipsitch, a professor at the Harvard School of Public Health, who was not involved in this study. "They're related. The pandemic is different from the seasonal H1, but it's still an H1."

...

http://www.healthnews.com/en/news/P...ned-pandemic-severity/1M0PL7n5HEjAsvBNtOTddZ/