From Alan Zelicoff, MD (full webpage
site: http://www.zelicoff.com):
[This page last updated on 5/23/09]
5/3/09: Commentary on Influenza A/H1N1 (Mexico Origin?)
A new influenza strain variously called “novel Influenza A” or
Influenza A/H1N1 “swine-origin influenza virus (S-OIV”) has been
isolated which is clearly causing disease (and some deaths) in Mexico
(where it apparently originated) and elsewhere. The outbreak –
now
confirmed as occurring on several continents – is by definition a
“pandemic”. The minimal set of questions facing public health
officials and political decision-makers are:
(1) will this turn into a severe pandemic that causes both severe
illness and mortality?;
(2) will it continue to spread?; and
(3) if it does appear to abate, will it return in the next influenza
season, perhaps with more severe manifestations necessitating a change
in the annual influenza vaccine at great expense, and perhaps
approaching a critical limit on the amount of influenza vaccine that
can be produced in time?
It now appears clear that the pandemic while widespread is not severe (pandemics don't have to
be "severe" in order to be pandemics, a point often overlooked).
I believe that there is sufficient evidence to conclude that there is
widespread immunity (not fully protective, but protective enough) so
that while there will certainly continue to be new cases -- just as
there are of seasonal influenza A in the northern hemisphere, soon to
be followed in a few weeks in the southern hemisphere -- I don't expect
high mortality, at least in the short run. However, whenever a
new strain of influenza A enters into circulation and is easily
transmissible from human to human, there is always a concern that a reassortment or recombination event may take
place. In both of these phenomena, a single host (usually thought
to be a pig or a bird, but humans are not excluded) can be infected
with two strains of influenza and when virus replication occurs,
reassembly of the virus inside of host cells can result in random
shuffling of the 8 genes making up the genome of the influenza virus
(reassortment) or there may
be cross-over of strands of homologous RNA during replication
(recombination). Out of these genetic events may emerge a new
influenza strains with either different (e.g. enhanced) virulence
properties or even extended host range (affecting, for example, other
mammalian species). I have pictured these phenomena below:
I have prepared a
working
document that I hope will provide both up-to-date information and some
useful analysis, highlighting uncertainties and statistically
meaningful trends so that serious readers can augment their
understanding of influenza per se, and judge the policy decisions that
are being made. This particular influenza – very much unlike H5N1
“avian” flu – spreads easily from person-to-person. This
transmissibility does not mean that there will be another global
pandemic on the impact scale of the devastating 1918 flu (or even the
mild but
nonetheless significant pandemics of 1957, 1977 and 1968), but it does
give cause for pause and careful thinking. My conclusions at the
moment are:
(a) the CDC/WHO recommendations for prudent self-isolation if one
develops
flu-like illness along with handwashing and other common sense
precautions are reasonable;
(b) it does not appear that this pandemic is any more severe than
recent seasonal influenza A episodes
(c) there is probably some pre-existing immunity in adults (and some
younger people) in most of the northern hemisphere above the Tropic of
Cancer and in the southern hemisphere below the Tropic of Capricorn
because of exposure either to circulating strains of influenza A or
previous vaccination. This may
explain the mild illness experienced so far in the US, Canada, New
Zealand, Spain, the UK and several other countries where seasonal
Influenza A is common (or where vaccination is common).
Lessons learned
Perhaps the most important lesson from this novel influenza outbreak is
that the US and most of the rest of the world lack a real-time, species
neutral disease surveillance system that can identify unusual (or
unusually severe) symptoms in human and animal populations early in the
course of an outbreak. Despite improvements in the International
Health Regulations of 2005 that call upon member nations of the WHO to
report any disease outbreaks of potential public health significance,
the tools to realize this necessary and laudable goal have not been
implemented. However, I believe such tools exist (see updates
below for more information).
My updates (hopefully
timely and accurate) can be read here by date:
I welcome comments and suggestions for improving (or correcting) this
document. All errors are mine and mine alone.
My e-mail
address is: zalan8587@qwest.net
