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. 2010 Jun 1;50(11):1487-92.
doi: 10.1086/652441.

Recipients of vaccine against the 1976 "swine flu" have enhanced neutralization responses to the 2009 novel H1N1 influenza virus

Jonathan A McCullers  1 , Lee-Ann Van De Velde, Kim J Allison, Kristen C Branum, Richard J Webby, Patricia M Flynn
Affiliations

Recipients of vaccine against the 1976 "swine flu" have enhanced neutralization responses to the 2009 novel H1N1 influenza virus

Jonathan A McCullers et al. Clin Infect Dis. .

Abstract

BACKGROUND. The world is facing a novel H1N1 influenza pandemic. A pandemic scare with a similar influenza virus in 1976 resulted in the vaccination of nearly 45 million persons. We hypothesized that prior receipt of the 1976 "swine flu" vaccine would enhance immune responses to the 2009 novel H1N1 influenza strain. METHODS. A prospective, volunteer sample of employees aged > or = 55 years at a children's cancer hospital in August 2009 was assessed for antibody responses to the 2009 pandemic H1N1 influenza virus and the 2008-2009 seasonal H1N1 influenza virus. RESULTS. Antibody responses by hemagglutination-inhibition assay were high against both the seasonal influenza virus (89.7% had a titer considered seroprotective) and pandemic H1N1 influenza virus (88.8% had a seroprotective titer). These antibodies were effective at neutralizing the seasonal H1N1 influenza virus in 68.1% of participants (titer > or = 40), but only 18.1% had detectable neutralizing titers against the pandemic H1N1 influenza virus. Of 116 participants, 46 (39.7%) received the 1976 "swine flu" vaccine. Receipt of this vaccine significantly enhanced neutralization responses; 8 (17.4%) of 46 vaccine recipients had titers > or = 160, compared with only 3 (4.3%) of 70 who did not receive the vaccine (P = .018 by chi(2) test). CONCLUSIONS. In this cohort, persons aged > or = 55 years had evidence of robust immunity to the 2008-2009 seasonal H1N1 influenza virus. These antibodies were cross-reactive but nonneutralizing against the 2009 pandemic H1N1 influenza strain. Receipt of a vaccine to a related virus significantly enhanced the neutralization capacity of these responses, suggesting homologous vaccination against the 2009 pandemic H1N1 influenza virus would have a similar effect.

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Conflict of interest statement

All authors declare no competing interests.

Figures

Figure 1
Figure 1
Phylogenetic tree (distance method [22]) of the HA1 region of HAs from representative human epidemic and pandemic H1N1 influenza viruses from 1918 to the present.
Figure 2
Figure 2
Antibody titers by A) hemagglutination-inhibition (HI) and B) microneutralization (MN) methods against the 2008-2009 seasonal H1N1 and the 2009 pandemic H1N1 influenza viruses, stratified by age. The dotted line in (A) represents the breakpoint for presumed seroprotection.
Figure 3
Figure 3
Microneutralization titers against the 2008-2009 seasonal H1N1 and the 2009 pandemic H1N1 influenza viruses, stratified by receipt of “swine flu” vaccine in 1976.
See this image and copyright information in PMC

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