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A potpourri of influenza issues
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This month’s commentary is a variety of gleanings encompassing several topics, but most dealing with several influenza-related issues; yes, it’s that time of year again!
In December, it was reported that a survey of more than 4,000 adults aged 18 or older carried out by the Rand Corporation in mid-November revealed the following rather startling information: approximately 30% had already received the vaccine this fall, 17% said they intended to be immunized, and the balance – 53% – said they had no intention of taking the vaccine. Reasons cited for not being vaccinated included the usual litany of excuses, ranging from not enough time, to perceived lack of need, fear of reactions or actually getting influenza, lack of physician recommendation and the like. Thus, we as infectious disease physicians and the public health community face an enormous and continuing challenge in public education.
This was the first ever such survey, so there are no data from previous years for comparison. The survey was sponsored, at least in part, by the pharmaceutical companies that produce the vaccine and it is not difficult to understand why. At least five pharmaceutical companies now produce almost 150 million doses of influenza vaccine for the American market annually and they are legitimately interested in selling it. If the vaccine is not selling, they would like to know why.
Challenging issues
Efforts to vaccinate health care personnel and children have encountered some challenging issues. Health care workers, a population one might think would be highly educable, are proving not to be so. Reports from several countries note similar vaccination rates for HCWs, well below 50%. One hospital in the United States (which shall go unnamed) took the distinctly unusual step of making receipt of influenza vaccine a condition of employment! Management eventually backed down on that one. The State of New Jersey passed a law requiring influenza vaccination for all children aged 6 months to 5 years before they could attend licensed day care or preschool programs. According to a recent article in The New York Times (Jan. 4, 2009) this law may well be tested in the courts, as schools have now reopened after the holidays and there have been numerous protests by parent groups.
Several times last year, I alluded in this space to the ongoing debate about overestimates of the benefits of influenza vaccine in the elderly, especially in preventing influenza mortality. In observational studies, vaccine recipients appeared to have a mortality benefit that was demonstrable even before influenza season began! This issue was debated further at the ICAAC/IDSA joint meeting this past October. In one poster presentation from the Kaiser-Permanente group in California, the dimensions of the so-called “healthy recipient” bias were explored by examining the relationship between age, underlying risk and influenza vaccination. The relationship was found to be curvilinear; up to the 90th percentile of increasing risk, vaccination increased, but then fell off after the 90th percentile. The same was true for age, with vaccination rates declining after age 80 in women and age 85 in men. Looked at another way, vaccination rates increased as mortality rates rose to about 5%, then declined as the death rate exceeded 5%. The authors concluded that their results were consistent with a “healthy recipient” effect, thus tending to make the vaccine look more effective than it actually is. (Baxter B, Fireman B, Lee J, Abstract G1-1206.) (See page 21 in this issue for more information about this study.)
Increasing resistance
Increasing resistance of certain influenza viruses to the neuraminidase inhibitor, oseltamivir, has resulted in a recent modification to CDC’s recommendations for influenza prophylaxis and treatment. So far this year, both influenza A H3N2 and H1N1 are circulating, as well as influenza B, and it is still too early to know which strain or strains will predominate where. The adamantanes, of course, have no activity against influenza B, and there is widespread resistance to influenza A H3N2 viruses. For the last several years, increasing proportions of influenza A H1N1 isolates have been resistant to oseltamivir, but remaining fully susceptible to the second neuraminidase inhibitor, zanamivir. This set of circumstances has resulted in the need to be very aware of local, regional or state surveillance data, to inform the decision about which drug to use for prophylaxis or treatment.
Using a test to distinguish influenza A from B:
1. If a patient is positive for influenza B, then use either oseltamivir or zanamivir if treatment is indicated.
2. If a patient is positive for influenza A, use zanamivir if treatment is indicated. Oseltamivir could be used only if there is surveillance data indicating a high likelihood that the circulating virus is influenza A H3N2.
3. If one is uncertain or doesn’t know, oseltamivir and rimantadine is an acceptable combination therapy.
4. Consult the CDC recommendations for chemoprophylaxis recommendations, but the issues are similar.
The expected increase in seasonal influenza in the United States is occurring, but so far there is nothing to suggest an unusually severe outbreak. The situation is apparently sharply different in Europe, however, and Great Britain is experiencing an unusually intense outbreak of influenza A H3N2. General practitioners in England and Wales reported sharp increases in the number of patients seen with influenza-like illnesses during the last several weeks of December (the approximate equivalent of the U.S. Sentinel Physician Surveillance Network). Public health officials there are suggesting this may be the most intense outbreak in the last 20 years. There is no evidence thus far, however, of significant antigenic drift which might render the vaccine less efficacious.
If this is happening in the United Kingdom, can the United States be far behind? Maybe, for there is by no means a 1:1 correlation of “severity” of influenza outbreaks in various countries around the world – even when caused by the same strain.
Finally, there is good news (for a change) on the pandemic vaccine front – at least in the European Community. The Committee for Medicinal Products for Human Use (CHMP – the approximate equivalent of FDA’s Vaccines Advisory Committee) has recommended approval of a cell-culture based pandemic influenza vaccine produced by Baxter Laboratories in the Czech Republic. It is said to be a “mock-up” vaccine, initially prepared with an early H5N1 virus.
If a pandemic is ever declared by WHO, the actual pandemic strain would be inserted into the production process. The big advantage is speed, since the pandemic strain would not need to be modified to grow in eggs; the production process is somewhat faster, as well. Assuming approval by the European Medicines Agency (EMEA – the approximate equivalent of the FDA) this would represent the second pandemic vaccine approved and “ready to go” within the European Community.
I anticipate Baxter will seek licensure of their cell-based vaccine in the United States as well.