H1N1 Swine `Flu Is almost Here!
By Dr. Rizwana Rahim
Chicago , IL
It’s almost here, 2009 H1N1 (swine ‘flu) virus ! It appeared in mid-April 2009 (and never did actually leave the US) and its return in the Northern Hemisphere is expected early this Fall as the flu season is set to begin and spread with schools and colleges around the country now re-opened, and as the frequency of closer human contacts also increases.
To fight it, FDA has just approved four vaccines to be manufactured by pharmaceutical companies well-experienced in this area ( CSL Limited, MedImmune LLC, Novartis Vaccines and Diagnostics Limited, and Sanofi Pasteur Inc.) using the same processes as in other flu vaccines, to be available to public in about three weeks. And, like other flu vaccines, the new H1N1 vaccine formulations are produced with or without the mercury-containing preservative, thimerosal. People concerned about mercury thus have an option. CDC also recommends antiviral drugs such as Oseltamivir or Zanamivir.
All this will, as usual, be strictly supervised by FDA, and like seasonal ‘flu, the 2009 H1N1 is expected to be highly contagious, as we saw in April, and spread by personal contact (coughing and sneezing, and touching virus-covered surfaces). President Obama himself reminded the children what to do when they show flu symptoms. Various government departments (CDC, FDA, NIH agencies, etc) have put out helpful public health and safety information on seasonal and H1N1 flu.
Seasonal flu symptoms vary from mild to severe, and there are some groups considered at higher risk. According to CDC data, people older than 65, children under 5, pregnant women and people with chronic health problems and conditions. Most people recover from seasonal flu, but it could also lead to death: on the average, each year, about 200,000 people are hospitalized with flu-related symptoms (about 10%, or 20,000, being children under 5), and about 36,000 die annually from flu-complications. Among those hospitalized, about 60% are older than 65 and most of those that die (90%) belong to that older group.
CDC studies, based on the samples collected from 2009 H1N1 cases since April, showed that about 33% of people older-than-60 had antibodies against H1N1 virus, while no children and very few among the under-60 group had this antibody. Clearly, those under-60 and most children under-5 seem susceptible, but it is not known how many of the over-65 group would be protected by the amounts of antibodies they already have against H1N1, against the new wave of H1N1 this Fall. Among the clinical confirmed cases of H1N1, about 79% were people under-30, whereas only 2% belonged to the over-60 group.
To put it simply, more people under-25 seem to be at higher risk than those older than 65. This is very different from the profile of usually-susceptible to seasonal flu over the years. However, health conditions that make one susceptible to seasonal flu also make them equally so to H1N1. Those infected with both viruses (seasonal and H1N1) can, up to a week or so, spread the infection to others.
In addition to known flu symptoms, people infected with H1N1 also report diarrhea and vomiting. Another significant difference from seasonal flu, as mentioned, is that people older than 64 do not seem, so far, to be at higher risk of H1N1. And out of those hospitalized with 2009 H1N1, a large majority (70%) also had health conditions (diabetes, heart- and kidney-related problems, asthma, and pregnant women), all also considered ‘ high risk’ for seasonal flu.
The apparent ‘immunity’ among the older-than-64 group has introduced an interesting twist, dating back to 1976. This week, The New England Journal of Medicine (NEJM) has published a group of papers with interesting but preliminary results.
In 1976, Americans (43 million) were vaccinated against well-publicized fears of swine flu that did not materialize later that year. One CDC study by Jackie Katz et al. who have since last May been analyzing frozen serum samples from those vaccinated in 1976, shows that over 60% of the serum samples from those adults had antibody levels (titers) of 160 or more when their serum was exposed to 2009 H1N1 virus; similar percent of samples also showed similar antibody levels when exposed to the 1976 swine virus itself. The study also found that those born before 1930 (including survivors of the 1918 epidemic) had antibodies that recognized and strongly responded to H1N1 virus: those born between 1910-1929, had antibody concentrations of 80 or more against H1N1 (titers of 40 or more are considered ‘protective’, according to most immunologists); similar antibody concentrations (80 or more) were found in 34% of those born before 1950. This suggests that the exposure to 1918 pandemic virus (and its descendants till about 1930) may still have antibody levels sufficient enough to fight against 2009 H1N1. In most adults, a single vaccination provides antibody levels that can be considered ‘protective’.
A recent Japanese study reported in NEJM, also found ‘protective’ antibody levels in the serum of Japanese adults who were also exposed to the 1918 Swine flu epidemic, but not in those born after 1920. Serum from older Europeans tested by CDC showed lower antibodies levels than Americans, perhaps because of a greater protection in Americans after the 1976 vaccination. For the past 20 years, vaccinations to seasonal flu did not provide protection against H1N1.
The family tree of 2009 HINI dates back at least to the 1918-1919 pandemic, but the real source of its introduction to humans is still unknown. Two years later, humans may have introduced into pigs, in which the virus seems to have remained unchanged till at least 1990s (this virus is not transmitted through food from pigs). But early swine flu lost some of its virulence to become season flu in humans for the past 40 years. The early human H1N1 strains that seemed to have disappeared in 1957 re-emerged in 1976, both strains genetically close. The 2009 strain contains elements from both swine and human viruses: it keeps H1 (a hemagglutinin protein) from the original swine strain; both almost identical. The 2009 H1N1 is like a 1931-like swine virus, according to Brian Murphy (NIAID/NIH) who supplied the 1976 serum samples to the Katz study.
Some scientists have raised questions about the study results, but how ‘protective’ will the new vaccinations be against any new strain of virus, no one can say for sure because viruses undergo changes so often, and the vaccinations against the new strain are prepared from samples of old virus strains, with some accommodation for changes to come. Same goes for H1N1 (its April 2009 strain used for vaccination against H1N1 this Fall). So, no one knows for sure, but the preparations for a new wave of H1N1 this Fall seem to be well-supported by data and look like they should be effective.
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