Sunday, July 19, 2009

Swine Influenza Pandemic: Important Questions and Answers

Q: How virulent is this virus?
A: It appears to be about as deadly as usual flu viruses--but with the major caveat that younger people are hardest hit. CDC reports 263 deaths and 40,000 confirmed cases in the US, but expects that over 1 million have been infected. The UK reported its 15th death on July 10, with 9,718 confirmed cases. Reuters reported this was the first entirely healthy person with H1N1 in the UK to have died. But on July 17, the UK announced there have been 55,000 cases and 29 deaths.

This virus probably spreads more easily than recent flu virus strains, since few people (mainly those in their 50s or older) appear to have any pre-existing immunity. There is no evidence the virus has become more virulent since the pandemic began.

CDC announced that pandemic flu activity has dropped for the third week in a row on July 17, though cases are apparently climbing across the pond.

Q: How can it be effectively treated?
A: I have seen no study of the effectiveness, if any, of Tamiflu (Oseltamvir) or Relenza (Zanamivir) against Swine H1N1. According to the manufacturer's label, Tamiflu reduced the duration of (non-pandemic) influenza symptoms by 1.3 days compared to patients receiving placebo in prelicensure clinical trials. Whether it can save lives remains an open question. From the London Times:
"The most comprehensive scientific assessment of Tamiflu and Relenza, produced by the Cochrane Collaboration this year, found that though they were effective in preventing or curtailing symptoms and complications of seasonal influenza, it was currently impossible to gauge their effectiveness in a pandemic, and little evidence to suggest that they would stop its spread. But it still recommended their use. For the time being, they’re the best we’ve got. "
CDC, with the most extensive data on Swine H1N1 deaths of any country, has still not informed clinicians of the causes of death and effective treatments.

Fortunately, the Australian government has provided this guidance to their clinicians.

Q: Will Swine H1N1 develop resistance to Tamiflu?
A: Probably. There are already a few reports of resistance from 3 countries. The different H1N1 virus that caused most of last year's influenza cases, and was predicted to return (the 2009-10 flu vaccine was formulated against it and two other viruses) was virtually 100% resistant to Tamiflu, and resistant to Relenza as well.

After receiving a course of Tamiflu, from 1.3% to 8.6% of post-treatment viral isolates showed Tamiflu resistance, according to the Tamiflu label. So resistance is likely to spread soon.

Q: Does anticipation of Tamiflu resistance make the need for vaccine more urgent?
A: Not really, since we do not know if Tamiflu is helping to prevent serious illness and deaths.

Q: Isn't a vaccine a necessity?
A: A safe and effective vaccine against this new pandemic virus would be wonderful, especially for high-risk individuals.

The problem with a vaccine is that governments want one available very quickly. The UK expects to have some vaccine available by the end of August (yes, that is only 6 weeks from now). The US hopes to begin vaccinations in late September or October. But achieving that kind of speed creates a host of problems that are being discussed by vaccine and public health professionals, outside public view.

If you want a new vaccine, designed against a never-before-seen virus, you will not know how effective and safe it is until you test it. But with the virus upon us, every week of testing sets back its use by a week. If the vaccine were to undergo the usual duration of testing, it might not be available for years. That is not acceptable to WHO and other public health agencies.

If you want at least a billion doses (which would correspond to one dose per person in the wealthy countries of the world) it will take a number of months for production under the best of circumstances. But today's circumstances are not the best. The CDC-supplied attenuated virus is producing a disappointingly low pandemic flu vaccine yield.

But there is a way out. It involves using novel adjuvants along with vaccine antigens. These adjuvants stimulate the immune response considerably. You require a lot less vaccine antigen with a new adjuvant (an estimated 1/5th as much), and there are even hopes that the immunity induced will be broader and stronger than with standard vaccinations. The immunity might even be effective against a mutated, more virulent virus. There is just one catch: the adjuvants that could induce such strong immunity may not be safe. Or they may be unsafe in certain patient populations, such as infants and/or those genetically predisposed to autoimmunity.

In December 2008, only 7 months ago, FDA and NIH held a 2-day meeting to discuss the types of research that could be done to evaluate the safety of such adjuvants. Then, unexpectedly, the H1N1 pandemic hit. And the plans that were slowly progressing to respond to an avian flu epidemic in the far future suddenly switched into prime time, absent the desired safety data.

Two new adjuvants being prepared for a pandemic flu vaccine (ASO3 and MF59) contain "oil in water" emulsions. The oil is squalene, which is a cholesterol precursor. However, when injected, squalene may cause arthritis or autoimmune effects. The US government recently promised to purchase 119 million doses of ASO3 and MF59, made by Glaxo-Smith Kline and Novartis, for new pandemic flu vaccines.

This is a very complex subject and I will be writing a lot more about it in the next few days.

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