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


  1. Perz CM, Ferres M, Labarca JA. Pandemic (H1N1) 2009 reinfection, Chile. Emerg Infect Dis 2010;16:156-57.
  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. . Accessed February 5, 2018.


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

Are GI symptoms such as nausea, vomiting, and diarrhea common in patients with influenza?

Typically, GI symptoms are more prominent in children with influenza than adults but during the H1N1 epidemic in 2009 (which has subsequently become endemic), up to 26% of hospitalized adults with H1N1 infection had abdominal pain or vomiting and up to 25% had diarrhea (1). 

In fact, H1N1 virus has been isolated from stool of adult hospitalized patients (2,3) and receptors of influenza virus have been identified in human GI epithelial cells, the correlation between GI symptoms and isolation of virus from stool is poorly defined (4).

Interestingly, the mechanism involved in influenza-mediated intestinal injury may have less to do with direct invasion of the intestinal mucosa by the virus and more to do with immune mediated changes  related to alterations in the intestinal microbiota induced by influenza virus infection itself (4,5)! 

Aside from direct or indirect effects of influenza virus on the GI tract, oseltamivir and non-steroidal anti-inflammatory use may also contribute to GI symptoms (4).


Liked this post? Download the app on your smart phone and sign up below to catch future pearls right into your inbox, all for free!

Subscribe to Blog via Email

Enter your email address to subscribe to this blog and receive notifications of new posts by email.


  1. Writing Committee of the WHO Consultation on Clinical Aspects of Pandemic (H1N1) 2009 influenza. Clinical aspects of pandemic 2009 influenza A (H1N1) virus infection. N Engl J Med 2010;362:1708-19.
  2. Yoo SJ, Moon SJ, Kuak E-Y, et al. Frequent detection of pandemic (H1N1) 2009 virus in stools of hospitalized patients. J Clin Microbiol 2010; 48:2314-2315.
  3. Minodier L, Charrel RN, Ceccaldi PE, et al. Prevalence of gastrointestinal symptoms in patients with influenza, clinical significance, and pathophysiology of human influenza viruses in faecal samples: what do we know? Virol J 2015;12:215.
  4. Shu Y, Li CK, Gao R, et al. Avian influenza A(H5N1) viruses can directly infect and replicate in human gut tissues. J Infect Dis 2010;201:1173-7.
  5. Wang J, Li F, Wei H, et al. Respiratory influenza virus infection induces intestinal immune injury via microbiota mediated Th17 cell-dependent inflammation. J Exp Med 2014;211:2397-2410.
Are GI symptoms such as nausea, vomiting, and diarrhea common in patients with influenza?