# 4000
In a short, and pretty straight forward letter to the NEJM, David N. Fisman, M.D., M.P.H. at the University of Toronto writes about the limited immunity that those over the age of 53 appear to have to the H1N1 pandemic virus.
Those born between 1957 and 1975 appear to have less immunity than the boomer generation, but more than those born after 1975.
I’ve posted a few excerpts below, but follow the link to read the letter in its entirety.
Older Age and a Reduced Likelihood of 2009 H1N1 Virus Infection
Volume 361:2000-2001 November 12, 2009 Number 20
Figure 1. Age-Related Probability of Seasonal Influenza A and 2009 H1N1 Influenza in 11,560 Tested Patients.
Patients who were born after 1957 (i.e.,
53 years of age) have an increased risk of infection with the 2009 pandemic influenza A (H1N1) virus. The results of testing show no significant relationship between age group and the risk of infection with seasonal influenza A viruses (either H3N2 or H1N1).
<SNIP>
Among persons who were at risk for infection with 2009 H1N1 virus, being born before 1957 was associated with a lower infection risk. The reduced number of infections was not simply a reflection of decreased testing in this group.
The mechanism for this association is unclear but is compatible with the reported age-related increase in the prevalence of neutralizing antibody titers against the 2009 H1N1 virus3 and may reflect some immunity to infection as a result of exposure to similar viruses in early life.
Maximally effective host immune responses to influenza may be generated by early-life infections.4 These findings are consistent with the high frequency of outbreaks of 2009 H1N1 influenza in schools5 and the decreased frequency of outbreaks in long-term care facilities that have been associated with this pandemic virus to date.
For more background on the possible causes of increased immunity among the older population, you may wish to refer to a blog I wrote in October entitled Two H1N1 Immunity Studies from the EID Journal.
That blog looked at two new studies, published online ahead of print in the CDC’s Journal of Emerging Infectious Diseases, hypothesize that over time exposure to other circulating influenza strains – or perhaps repeated seasonal flu vaccinations – may have helped to provoke a limited immune response in some people to this novel pandemic strain.
Preexisting Immunity to Pandemic (H1N1) 2009
Z. Xing and C.J. Cardona (186 KB, 5 pages)Serologic Survey of Pandemic (H1N1) 2009 Virus, Guangxi Province, China H. Chen et al. (155 KB, 4 pages)
