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Commentary
H1N1 Re-Infections
Confirmed
Recombinomics
Commentary 13:50
January 6, 2010
The above comments are from a report in the current EID of re-infections by H1N1 in lab confirmed cases treated with Tamiflu in Chile. This report follows media reports of other cases in the United States with at least two lab confirmed infections in individual patients. The other reports had larger gaps in disease onset dates and those re-infections are similar to many anecdotal reports.
Many of these re-infections can be explained by a weak response to infections with low viral loads. The above group of three patients had recurrences within a few weeks of recovery, which may have been too soon for optimal protective immunity. However, other media reports describe lab confirmed cases that are 6 weeks to 3 months apart. Since H1N1 has only recently begun to evolve at a more rapid pace, it is unlikely that the re-infections were due to significant genetic changes.
Additional evidence for weak responses comes from the pandemic H1N1 clinical trial in Australia over the summer. Although prior pandemic H1N1 infections were among the exclusion criteria, 31% of patients enrolled had titers of 40 or higher at baseline, suggesting that many cases were mild and the patient did not get tested for H1N1 and did not associate the symptoms with H1N1.
However, these patients were vaccinated in the trial and a high percentage had a significant response, increasing titers four fold or higher. These data provided addition evidence that these initial infections produced sub-optimal immune response and protection.
Thus, several sources suggest initial immune responses to pandemic H1N1 are sub-optimal, so re-infections with similar or identical H1N1 are common, suggesting subsequent pandemic waves can be driven by an increase in viral load or minimal genetic changes.
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