Evaluation of the efficacy and cross-protectivity of recent human and swine vaccines against the pandemic (H1N1) 2009 virus infection

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 microg 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 microg 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 approximately 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.

Figure 1. Alignment of the HA1 portion of the HA molecule of H1 influenza viruses.

The amino acid sequences were aligned using Clustal_X , , and the phylogenetic tree was generated by the neighbor-joining method using the tree drawing program NJ plot . The scale represents the number of substitutions per nucleotide. Branch labels record the stability of the branches over 100 bootstrap replicates. Only bootstrap values ≥60% was shown in each tree. The A/California/04/2009 virus shares about 70% and 88.4% amino acid sequence homology with the seasonal human (A/Brisbane/59/2007*) and Korean swine (A/Swine/Korea/CAN01/2004+) H1N1 viruses, respectively.

Figure 2. Hemagglutinin inhibition (HI) titers in ferrets administered with inactivated vaccines (a-Brisbane/59/07, a-CAN01/04, RgCA/04/09xPR8).

Groups of four 15- to 16-week-old ferrets were vaccinated intramuscularly with one or two doses each of inactivated vaccines containing 7.5 µl/dose of HA with 2% of aluminum hydroxide adjuvant, administered 2 weeks apart. Sera were collected from recipients after 2 weeks the last vaccine was administered and mean hemagglutinin inhibition (HI) titers against Brisbane/59/07, CAN01/04 and CA/04/09 viruses were determined (limit of detection: <20 HI units) expressed as the reciprocal of the highest dilution of serum that inhibits 8 HA units of virus (e.g., as 80 versus 1∶80). Data are mean ± standard deviation titers.

Figure 3. Monitoring of body temperature in ferrets and mini-pigs.

Mean body temperatures of ferrets (a) and mini-pigs (b) infected with the pandemic (H1N1) 2009 virus (CA/04/09) or the recent Korean swine H1N1 (CAN01/04) isolate, including naïve contact animals, were monitored daily for 11 days post infection. The range of normal body temperatures are indicated as broken lines. Standard error bars are shown.

Figure 4. Hemagglutinin inhibition (HI) titers against the pandemic (H1N1) 2009 or Korean swine H1N1 virus in mini-pigs vaccinated with two doses of a-CAN01/04 or RgCA/04/09xPR8.

Groups of two eight-week-old specific pathogen-free mini-pigs were vaccinated intramuscularly with one or two doses each of inactivated vaccines containing 7.5 µl/dose of HA with 2% of aluminum hydroxide adjuvant, administered 2 weeks apart. Sera were collected from recipients after 2 weeks the last vaccine was administered and mean antibody titers against CAN01/04 or CA/04/09 virus were determined by HI assays expressed as the reciprocal of the highest dilution of serum that inhibits 8 HA units of virus (e.g., as 80 versus 1∶80) with <20 HI units as the limit of detection. Data are mean ± standard deviation titers.

Figure 5. Gross pathological examination of lung tissue samples from infected and contact mini-pigs after challenge with the CA/04/09 virus.

Lungs of 2-dose vaccinated [7.5 µg HA of either a-CAN01/04 (a) or RgCA/04/09xPR8 (b)] and subsequently challenged mini-pigs, including naïve contact hosts, were harvested at 5 dpi to examine gross tissue morphological features after infection with the pandemic (H1N1) 2009 virus.