Inactivated seasonal influenza vaccines increase serum antibodies to the neuraminidase of pandemic influenza A(H1N1) 2009 virus in an age-dependent manner

Abstract

Levels of preexisting antibodies to the hemagglutinin of pandemic influenza A(H1N1) 2009 (hereafter pandemic H1N1) virus positively correlate with age. The impact of contemporary seasonal influenza vaccines on establishing immunity to other pandemic H1N1 proteins is unknown. We measured serum antibodies to the neuraminidase (NA) of pandemic H1N1 in adults prior to and after vaccination with seasonal trivalent inactivated influenza vaccines. Serum antibodies to pandemic H1N1 NA were observed in all age groups; however, vaccination elevated levels of pandemic H1N1 NA antibodies predominately in elderly individuals (age, ⩾60 years). Therefore, contemporary seasonal vaccines likely contribute to reduction of pandemic H1N1-associated disease in older individuals.

Figure 1.

Proportion of study participants showing neuraminidase inhibition (NI) titers. Serum samples from younger (age, 20–40 years) and older (age, 60–84 or ⩾85 years) adults were collected prior to and 4 weeks after vaccination with trivalent inactivated seasonal influenza vaccines with H1N1 components from A/Brisbane/59/2007 (Brisbane; 2008–2009 season) or A/Solomon Islands/3/2006 (Sol. Is.; 2007–2008 season) and tested against pandemic influenza A/Tennessee/1–560/2009 (TN) or corresponding seasonal vaccines. A, Predicted (curves) and actual (points) proportion of individuals in each age group with measurable neuraminidase inhibition titers prior to vaccination. The geometric mean titer and sample size (in parentheses) are indicated for each age group. B, Predicted (curves) and actual (points) proportion of individuals in each age group who seroconverted to either pandemic or seasonal influenza A(H1N1) strains after vaccination with the corresponding vaccine. Error bars show the standard error. N.D., not detected (titer below the detectable limit).

Figure 2.

Proportion of study participants showing hemagglutinin inhibition (HI) titers. Serum samples from younger (age, 20–40 years) and older (age, 60–84 or ⩾85 years) adults were collected prior to and 4 weeks after vaccination with trivalent inactivated seasonal influenza vaccines with H1N1 components from A/Brisbane/59/2007 (Brisbane; 2008–2009 season) or A/Solomon Islands/3/2006 (Sol. Is.; 2007–2008 season) and tested against pandemic influenza A/Tennessee/1–560/2009 (TN) or corresponding seasonal vaccines. A, Predicted (curves) and actual (points) proportion of individuals in each age group with measurable hemagglutinin inhibition titers prior to vaccination. The geometric mean titer and sample size (in parentheses) are indicated for each age group. B, Predicted (curves) and actual (points) proportion of individuals in each age group who seroconverted to either pandemic or seasonal influenza A(H1N1) strains after vaccination with A/Brisbane/59/2007 (solid lines and circles) or A/Solomon Islands/3/ 2006 (dashed lines and triangles). Error bars show the standard error.