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Outbreaks Raise H1N1 Re-Infection Concerns
"It's basically flu-like symptoms we're seeing," said Jacquelyn Astyk, the school nurse at J.F.K. "Our upsurge followed our homecoming week where a lot of students were together for activities and also with events in the community for Halloween, the haunted houses and that. Students are being together and we're seeing an increase in the flu symptoms
In the Iroquois Central School District, about 18-percent of its student body was out sick Tuesday.
The above comments describe two major flu outbreaks at schools in the Buffalo, NY area (see map). This area had widespread confirmed cases in the spring, and raise concerns that those infected in the spring are being re-infected in the fall. These protection failures raise concerns that the vaccine directed against spring sequences will fail to protect against re-infection.
These re-infections are not limited to the Buffalo area. Earlier reports described a second wave in Mexico in regions which were impacted in the spring, and anecdotal reports describe the same individuals infected in the spring and fall or twice in the fall.
Although re-infections have been noted in immune-compromised patients, the re-infections in areas like Buffalo appear to involve previously healthy individuals.
The re-infections could be linked to weak immune-responses to earlier infections, which may have been influenced by anti-viral treatment. However, this does not appear to be the case in patients infected with milder course that do not involve fever, because most do not believe they are infected with swine flu and the recover without treatment.
These re-infections may be linked to antigenic drift, which may be enhanced by infections with multiple sub-clades, either via mixtures within an infectious dose, or multiple infections due to high levels of circulating virus and efficient transmission.
School outbreaks have been widespread, and closing of entire school districts in select states like TX, TN, KY have highlighted the rapid spread of H1N1 leading to double digit absenteeism rates such as those described above.
These re-infections raise concerns because of increased drift, as seen in the latest CDC report on an H1N1 with a reduced titer, as well as the increasing detection of H1N1 with H274Y, conferring oseltamivir resistance, or PB2 E627K favoring growth at a lower temperature.
More information on the frequency of re-infections would be useful, although the limited testing of mild cases limits lab confirmations of such re-infections.