Can my patient contract influenza more than once in a season?

It’s not common but reinfection with influenza can definitely occur, either due to the same viral strain, or due to a different one altogether.

One study reported influenza reinfection due to H1N1 in otherwise healthy patients within 12-20 days of the original infection after an apparent period of full recovery. 1 There was no evidence of resistance to oseltamivir among isolates and all patients recovered after the second infection.

Reinfection with the same viral strain within 2-3 weeks of the initial bout of influenza shouldn’t be too surprising since it takes 4-7 weeks for antibody response to the infection to peak. 2 Reexposure to the same circulating strain of influenza virus (the season can last 6 weeks or longer) can then result in reinfection when the body hasn’t had enough time to make significant amount of protective antibodies following the first infection.

Another explanation is that more than 1 strains of influenza virus often circulate during any given season.   This places patients at risk of infection due to strains of influenza virus that do not confer significant cross-immunity between each other,  resulting in getting “the flu twice in 1 season.” 3

References

  1. Perz CM, Ferres M, Labarca JA. Pandemic (H1N1) 2009 reinfection, Chile. Emerg Infect Dis 2010;16:156-57. https://wwwnc.cdc.gov/eid/article/16/1/pdfs/09-1420.pdf
  2. Treanor JJ. Influenza viruses, including avian influenza and swine influenza. In: Mandell GL, Bennett JE, Dolin R, eds. Principles and practice of infectious diseases. 7th ed. New York: Elsevier; 2010. p 2265-2293.
  3. Rettner R. Can you get the flu twice in 1 season? Scientific American, LiveScience, February 4, 2018. https://www.scientificamerican.com/article/can-you-get-the-flu-twice-in-1-season/ . Accessed February 5, 2018.

 

Can my patient contract influenza more than once in a season?

Are neuraminidase inhibitors (NAIs) such as oseltamivir (Tamiflu) still effective for treatment of influenza in my hospitalized patient with greater than 48 hours of symptoms?

Although the sooner NAIs are initiated the more likely the odds of a favorable impact on the course of influenza, the FDA approval of these drugs was based on study in relatively healthy ambulatory patients not those who require hospitalization and are generally much sicker. There are no randomized studies but several observational studies support  the benefit of NAIs even when initiated after 48 h of onset of the disease.  One study reported improvement in survival even when treatment was delayed for 4-5 days after symptom onset (1), while others have reported more rapid viral clearance and clinical benefit in severe infections even when antivirals were initiated after 48 h (2).  

Collectively , these data suggest that in the presence of ongoing symptoms and likely active viral replication, NAI treatment should be seriously considered in hospitalized patients who are likely to have more severe disease. CDC recommends  “initiation of antiviral treatment as early as possible” in hospitalized patients, and states that “antiviral treatment might be effective in reducing morbidity and mortality in hospitalized patients even if treatment is not started until >48 hours after onset of illness.” (3)  

 

References

  1. Louie JK, Yang S, Acosta M, et al. Treatment with neuraminidase inhibitors for critically ill patients with influenza A (H1N1) pdm09. Clin Infect Dis 2012;44:1198-1204.
  2. Lee N, Ison MG. “Late” treatment with neuraminidase inhibitors for severely ill patients with influenza: better late than never?
  3. CDC. Antiviral agents for the treatment and chemoprophylaxis of influenza: recommendations of the Advisory Committee on Immunization Practices. MMWR 2011;60 (RR01):1-24.
Are neuraminidase inhibitors (NAIs) such as oseltamivir (Tamiflu) still effective for treatment of influenza in my hospitalized patient with greater than 48 hours of symptoms?