Study: Preexisting flu antibodies may impede broad immune response
Past exposure to influenza virus or antigens—whether by infection or vaccine—might reduce a person's ability to mount a broadly protective antibody response to the virus, a finding that could complicate efforts to develop a "game-changing" universal flu vaccine, according to a study yesterday in Science Translational Medicine.
US researchers analyzed the antibody response to the 2009 H1N1 virus over time in vaccinated people. They found that subjects with low levels of H1N1 antibodies before vaccination produced a broadly protective immune response against the hemagglutinin (HA) stalk—a part of the virus that does not change much across various strains and has been eyed as a promising site for a universal, or broadly protective, flu vaccine.
The investigators found, however, that people with high levels of preexisting H1N1-specific antibodies mounted a reaction that primarily targeted the HA head, leading to a weaker immune response. These subjects tended to be older and thus had encountered a wider range of H1N1 strains.
The findings suggest that prior exposure to influenza, including in vaccines, may actually leave people with fewer broadly protective immune cells, the authors note. This could well present a hurdle to the development of a universal flu vaccine.
Commenting on the study in a STAT story today, infectious disease expert Michael Osterholm, PhD, MPH, said, "So one of the key questions is going to be for any kind of game-changing flu vaccine is how do you overcome that? And to the extent that that occurs, when does it jeopardize protection if, for example, you create a vaccine against the … stalk versus the head?"
H5N2 avian flu confirmed for first time in France
A recent outbreak of avian flu reported in the media this week in France has been confirmed as being caused by the H5N2 strain, the first detection of that strain in the country, according to a report yesterday posted by the World Organization of Animal Health (OIE).
The outbreak is in the same general region as one caused by H5N1 reported to the OIE on Nov 25, and the country has had at least one other recent outbreak caused by an as-yet unidentified highly pathogenic avian flu strain, according to a report yesterday in Farmers Weekly, a UK publication. France's agriculture ministry had reported the two most recent outbreaks on Nov 29, according to French-language media.
The H5N2 outbreak began Nov 27 in Domme in Dordogne department in southwest France, French officials noted in the OIE report. H5N2 was confirmed in a sample from a dead gosling on Nov 30.
All told, 3 geese on a farm of 1,338 geese and ducks died, but the report attributes only 1 of the deaths to H5N2 avian flu. Three geese were also culled for sampling, then the entire flock was euthanized to contain the outbreak after nucleotide sequencing and polymerase chain reaction tests came back positive for the virus.
Officials have created 3- and 10-kilometer surveillance zones around the farm.
A rapid risk assessment published by the European Centre for Disease Protection and Control (ECDC) yesterday said the H5N1 strain is not related to H5N1 strains circulating elsewhere in the world but appears to have evolved from a low-pathogenic avian flu virus circulating on the continent.
Also, the ECDC said that a phylogenetic analysis of the H5N2 strain is under way to determine if it is related to H5N2 strains circulating elsewhere. So far no human illnessess have been linked to H5N2, the agency said.
Dec 2 OIE report
Dec 2 Farmers Weekly story
Nov 25 CIDRAP News scan on earlier H5N1 outbreak
Dec 1 CIDRAP News scan on initial reports of latest outbreaks
Dec 2 ECDC risk assessment