According to the CDC, here in the US about 60% of kids and 45% of adults get the flu vaccine. The results? About 21M people still end up catching the flu, with about 50% of them visiting a doctor for treatment - and about 15% of them actually ending up hospitalized. In any given year, 12,000-61,000 people die. I didn’t see how many sick days are attributed to the flu every year, but it’s fair to add that loss of productivity to the total burden of health care costs, misery, and death due to the flu.
No vaccine is 100% effective, and in some years health officials make incorrect predictions about which strains of flu will be most prevalent and end up preparing a vaccine with unusually poor effectiveness. Under these circumstances herd immunity matters, and with flu vaccination rates hovering around the 50% mark, it seems we don’t have it.
But what if we did? What if everyone in the US got the flu vaccine each year? Does the CDC (or anyone else) publish estimates of what could be achieved, in terms of public health, if flu vaccination were universal? How many illnesses, sick days, hospitalizations, and deaths would we have under such circumstances?
A full explanation of the modeling for herd immunity in general is here but you need to know R (the reproduction rate which is the number of secondary cases per new case introduced to use the model). Threshold for eradication R’ = R(1-v) where v = immune fraction.
From here we see that it’s mean R is 1.3 with a range of 0.9 to 2.1.
Saving us playing with the math itself the first article says that if R = 2 then 50% of the population being immune would lead to eradication by herd immunity.
Seasonal influenza vaccine effectiveness (VE) overall ranges from a low of 19% (2014 to 15 season) to 60 in 2010 to 2011. Eyeballing it it looks like mid-40s is a reasonable expectation. (Reality is that it is different in different sub-populations, higher VE in kids for example than in the elderly.)
So you can play with the math itself but roughing it out myself for the average year I get R’=1.3(1-0.45) = 0.71 under the eradication threshold of 1. For a year that R is highest of the range though, 2.1, and lowest VE, 0.19, R’= 1.7, not under eradication threshold.
Lastly here’s some information just on what you are looking for looking only at the elderly population which has less VE and high morbidity/mortality under different scenarios.
I’m assuming even if sub-eradication, you still get some sort of asymptotic decline in incidence rate? From which you can calculate “illnesses, sick days, hospitalizations, and deaths”. Also loss of GDP.
Some very, very quick googling suggests that the flu bounces back and forth between the N and S hemisphere, basically following winter around. From that, I would assume that Australia’s is based on either ours or somewhere in Northern Europe.
The flu seems to mutate as it travels, so it’s not that it’s an exact preventive, it’s their best guess for what will work. If Australia’s flu is responding to the H1N1 vaccine, we can use that. If that’s what they gave everyone and it’s not working, we’ll use something different.