The question of treatment duration is a very important one. This great post from James Freeman explains why many health insurance companies and national health services are going for the 8 week treatment. Its not because it is the best treatment option for the patient. It is because it is the best financial option for the treatment provider. If your health insurance or health care provider offers you 8 weeks treatment take it but back it up with at least an extra 4 weeks treatment using a generic equivalent. Look at it this way. If my maths is correct (not my strong point) 8 weeks treatment means about 1 in 12 people will relapse. 12 weeks treatment means about one in 20 will relapse. In other words doing the extra 4 weeks almost doubles your chance of not relapsing.
Sixteen weeks treatment is better than 12 weeks treatment but not by a huge amount. However it still improves your chance of a cure.
Where only 12 weeks dosing was looked at and the results were good but the results are better for longer treatment periods
We do know, from other studies in genotype 1 that rates of cure look like this:
4 Weeks <50%
8 Weeks 90%
12 Weeks 95% +5%
16 Weeks 97% +2%
20 Weeks 98% +1%
24 Weeks 98.5% +0.5%
So, as you can see, each extra 4 weeks (1 bottle of tablets) adds a little more to the cure rate, but not as much as the bottle before. Mathematically we are looking at approach to an asymptote like this (where the limit value is 100%)
The treatment duration (for mass treatment/population health/cost economics) is picked as a balance between cost and cure rate. For a system 90%+ cure rate for 1 unit of cost makes more sense than even 100% cure rate for 2 units of cost.
Genotype 3 remains the most difficult to cure in the first instance, and the most difficult to retreat so while it might not make sense for the system to fund 16 week treatments…
For more information on preventing Hepatitis C relapse and on how long you should consider treating with DAAs here is a link to HepMag https://www.hepmag.com/blog/reducing-chance-relapse-treatment-time and also a link to a blog post of mine on the subject