Seasonal trivalent inactivated influenza vaccine protects against 1918 Spanish influenza virus infection in ferrets

Abstract

The influenza virus H1N1 pandemic of 1918 was one of the worst medical catastrophes in human history. Recent studies have demonstrated that the hemagglutinin (HA) protein of the 1918 virus and 2009 H1N1 pandemic virus [A(H1N1)pdm09], the latter now a component of the seasonal trivalent inactivated influenza vaccine (TIV), share cross-reactive antigenic determinants. In this study, we demonstrate that immunization with the 2010-2011 seasonal TIV induces neutralizing antibodies that cross-react with the reconstructed 1918 pandemic virus in ferrets. TIV-immunized ferrets subsequently challenged with the 1918 virus displayed significant reductions in fever, weight loss, and virus shedding compared to these parameters in nonimmune control ferrets. Seasonal TIV was also effective in protecting against the lung infection and severe lung pathology associated with 1918 virus infection. Our data demonstrate that prior immunization with contemporary TIV provides cross-protection against the 1918 virus in ferrets. These findings suggest that exposure to A(H1N1)pdm09 through immunization may provide protection against the reconstructed 1918 virus which, as a select agent, is considered to pose both biosafety and biosecurity threats.

Fig 1

Protective efficacy of seasonal TIV (VAX) in ferrets following homologous virus challenge. The morbidity of ferrets was determined for 14 days following challenge with seasonal human H3N2 virus A/Perth/16/2009 (Perth/16) (A) or H1N1 virus A/Mexico/4482/2009 (Mex/4482) (B). For each virus challenge, three TIV-inoculated ferrets (open circle) and four PBS control ferrets (filled circle) were challenged with 10⁶ PFU of virus. Differences in weight loss between groups were analyzed by Student's t test (*, P ≤ 0.005). Error bars show standard deviations.

Fig 2

Seasonal TIV efficacy against virus replication of A/Perth/16/2009 (Perth/16) or A/Mexico/4482/2009 (Mex/4482) virus. The nasal cavities of ferrets were washed with 1 ml of PBS every other day starting 2 days p.c., and virus titers were determined in a standard plaque assay. Gray-shaded bars represent the results for unimmunized (PBS) control ferrets, and open bars represent the results for TIV-immunized ferrets. The data shown are mean values plus standard deviations (error bars) for 3 or 4 ferrets per group (A and B). Differences in viral titers of nasal washes between groups were analyzed by Student's t test (*, P ≤ 0.020; **, P ≤ 0.0005).

Fig 3

Clinical symptoms and viral shedding in TIV-immunized and control ferrets following 1918 virus challenge. (A) Mean weight loss observed among vaccinated (open circles) and PBS control (filled circles) ferrets following challenge with 10⁶ PFU of the 1918 virus. Nasal washes (B) and tissues (C) at 3 (left) and 5 (right) days p.c. were collected and viruses titrated in a standard plaque assay. Gray-shaded bars represent results for unimmunized (PBS) control ferrets, and open bars represent results for TIV-immunized ferrets. The data shown are mean values plus standard deviations (error bars) for 5 ferrets per group (A and B) and for 3 ferrets per group for each time period (C). Differences in viral titers between groups were analyzed by Student's t test (*, P ≤ 0.04; **, P ≤ 0.005; ***, P ≤ 3E-06).

Fig 4

Immunohistochemistry of 1918 TIV-immunized and control ferrets following 1918 virus challenge. Photomicrographs of lung tissue sections from control (A to D) and TIV-immunized (E and F) ferrets stained (in red) for the presence of viral antigen 3 and 5 days p.c. Viral antigen was found in bronchiolar epithelial cells and in desquamated cells in the lumen of bronchioles on day 3 p.c. (A and B), in cells of submucosal serous glands of the bronchus on day 5 p.c. (C), and in alveolar cells and macrophages on day 5 p.c. (D). TIV-immunized ferrets challenged with the 1918 virus examined at day 3 p.c. displayed milder lung lesions than controls, with no specific viral antigen staining detected on day 3 p.c. (E) and day 5 p.c. (F).