Abstract
The current pandemic (H1N1) 2009 virus remains transmissible among humans worldwide with cases of reverse zoonosis, providing opportunities to produce more pathogenic variants which could pose greater human health concerns. To investigate whether recent seasonal human or swine H1N1 vaccines could induce cross-reactive immune responses against infection with the pandemic (H1N1) 2009 virus, mice, ferrets or mini-pigs were administered with various regimens (once or twice) and antigen content (1.77, 3.5 or 7.5 µg HA) of a-Brsibane/59/07, a-CAN01/04 or RgCA/04/09xPR8 vaccine. Receipt of a-CAN01/04 (2-doses) but not a-Brisbane/59/07 induced detectable but modest (20–40 units) cross-reactive serum antibody against CA/04/09 by hemagglutinin inhibition (HI) assays in mice. Only double administration (7.5 µg HA) of both vaccine in ferrets could elicit cross-reactivity (30–60 HI titers). Similar antigen content of a-CAN01/04 in mini-pigs also caused a modest ∼30 HI titers (twice vaccinated). However, vaccine-induced antibody titers could not suppress active virus replication in the lungs (mice) or virus shedding (ferrets and pigs) of immunized hosts intranasally challenged with CA/04/09. Furthermore, neither ferrets nor swine could abrogate aerosol transmission of the virus into naïve contact animals. Altogether, these results suggest that neither recent human nor animal H1N1 vaccine could provide complete protectivity in all animal models. Thus, this study warrants the need for strain-specific vaccines that could yield the optimal protection desired for humans and/or animals.
Highlights
Influenza A virus is the cause of recurrent influenza epidemics and from time to time, global pandemics
Serum specimens collected from children and adults that were immunized with recent seasonal influenza vaccines suggest that receipt of such vaccines is unlikely to elicit protective antibody immune response to the pandemic (H1N1) 2009 virus [19,20]
Since the causative pandemic (H1N1) 2009 influenza virus is considered a novel strain, it appears that currently available human influenza virus vaccines could not elicit cross-reactive antibodies to the current pandemic virus [19,20,21]
Summary
Influenza A virus is the cause of recurrent influenza epidemics and from time to time, global pandemics. A global pandemic was declared anew last June 11, 2009 by the World Health Organization (WHO) due to the emergence and rapid worldwide spread of a novel influenza A (H1N1) virus, hereafter referred to as pandemic (H1N1) 2009 virus [2,3]. The mortality rate due to infection with the pandemic virus among humans is low at present, establishment of the pandemic virus in a new host may yield more virulent strains. Pigs are strongly heralded as ‘‘mixing vessels’’ for the exchange of genetic materials between human and animal influenza viruses [14,15,16,17] potentially enhancing pathogenicity and lethality of the reassortant virus
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