Friday, April 10, 2009

Vaccinating against cervical cancer - the problem with vaccines

Many people don't have a good appreciation of what vaccines can do, or ought to be doing.

Essentially vaccines are supposed to raise the immunity against a particular disease through the administration of an antigen associated with the disease, e.g. a virus antigen, so that the body can 'learn' to build up an immune response to it. The 'learning' creates an immunological memory which may last for a variable period of time.

The problem with vaccines, is that it is difficult to assess the true efficacy of a vaccine. At best one can only measure an antibody response. The assumption is that the better the antibody response, the more efficacious the vaccine. The follow-on assumption is that the presence of the antibody response 'protects' against the infection. In the case of cervical cancer, there are two principal assumptions...i] the raised antibody levels will completely protect against the papilloma virus infection at the cervix (not so easy to assume)....and ii] the protection against infection will be translated into protection against cervical cancer (even harder to assume). So essentially the true efficacy of the vaccine depends on two unproven (though logical) assumptions.

On the other side of the coin, vaccines are notably associated with a tendency to induce the body's immune system to turn upon itself and cause various diseases. This is uncommon but a real and recognizable phenomenon. The problem with the GSK vaccine is that it uses a novel way of stimulating the immune system that has not had the same history of safety as the Merck vaccine. The toxicity is not predictable and may not develop until many years after administration of the vaccine. Hence the risk is not easily assessed with short term (or often even with much longer term studies) clinical studies.

So for new vaccines such as the cervical cancer vaccines, neither clinical efficacy nor safety data can be fully relied upon without the need to make all kinds of assumptions and promises of success.

But the vaccine industry is a billion dollar one. It has been estimated that the annual market for each vaccine is about US$2 billion. Hence the market pressures for GSK and Merck to keep flogging their respective vaccines, and to encourage their use even beyond the approved indications (off-label use).

The public needs to be less gullible and a bit more guarded about overextended claims. The vaccines have potential to do a lot of good, but do be cautious. The added difficulty here is that our regulators (HSA) are not totally free from the pressures from the heavy muscled pharmaceutical industry. In this instance, one of the protagonists to this story is a company with a very strong industrial and academic presence in Singapore. I truly hope that the regulator is adequately provisioned to china-wall against industry interests and can continue to regulate wisely and independently.

Fingers and toes crossed.

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