I've been looking at the effectiveness of Flu vaccines, which are in my subjective opinion abysmal, and the concept of herd immunity. I see many articles which argue that we all need flu shots to help support the weaker individuals via herd immunity. However, I see very few documents actually indicating how effective this process is.
Most of what I have found on the topic is interested in the Herd Immunity Threshold (HIT), which appears to be the point where vaccinations drive the Rq of the disease (reproductive rate in the presence of the vaccinations) below 1 such that the disease spreads to fewer and fewer people with each generation, like removing the heat from a fire such that it cannot sustain itself.
There are two particular aspects of this which I believe are required to answer the question which I cannot seem to find a good answer for, which have been preventing me from answering my question:
- What is R₀, the basic reproductive rate, for influenza? I have seen estimates ranging from 1.2 to 3. As best as I can tell, even a poor vaccine would be very effective if it was 1.2 but it seems like it would do very little against the higher R₀ values.
- How substantial of a knee in the curve is there regarding the number of immunized individuals vs. the herd immunity effects? If there is no substantial knee in the curve, that should indicate that there are valid herd immunity arguments for influenza even if the vaccines are substantially ineffective. If the knee in the curve is sharp, then herd immunity arguments would only be valid if we could reach that threshold.
It appears some of these questions may have been answered in "The vaccination coverage required to establish herd immunity against influenza viruses" by PedroPlans-Rubió in 2012, but I do not have any access to Preventive Medicine, the journal it was published in.