A Pox on the Taxpayer
A handful of countries recommend the chickenpox (varicella) vaccine for all children and an even smaller group have a chickenpox booster on the schedule. The US leads the pack of countries with a 2 shot schedule, and following along are Ecuador, Saudi Arabia, Germany, Greece, and part of Australia.
Some countries give the shot to adolescents, others offer it to members of “risk groups”… and a few have a one-shot schedule for toddlers: Canada, Costa Rica, Uruguay, Cyprus, Latvia, and Korea. A grand total of 26 countries offer the shot in one way or another. 
The US was the first country to recommend the shot for all toddlers, in 1996 :
…. empiric data on medical utilization and costs of work-loss resulting from varicella were used. The results of this study, which were determined using an estimated cost of $35 per dose of vaccine and $5 for vaccine administration, indicated a savings of $5.40 for each dollar spent on routine vaccination of preschool-age children when direct and indirect costs were considered. When only direct medical costs were considered, the benefit-cost ratio was 0.90:1.  (emphases added)
But it turned out that a single shot of varicella vaccine didn’t work to suppress chickenpox.
…varicella outbreaks have regularly been observed in populations with high vaccination coverage and are the cause of sizable disease and economic impact for public health departments and the US health system overall. To further reduce varicella disease burden, a routine 2-dose varicella vaccination recommendation was approved by the Centers for Disease Control and Prevention (CDC) Advisory Committee on Immunization Practices (ACIP) in June 2006 (first dose for children 12–15 months of age, second dose for children 4–6 years of age) . 
The single-shot regimen showed a narrow margin of benefit only when placed alongside income lost by parents staying home to care for sick children.
But when the one-shot program failed, the ACIP came up with another cost/benefit justification for the second shot where the evidence….
….included ongoing disease burden and varicella-zoster virus transmission, including transmission from breakthrough cases to high-risk persons that may lead to severe disease and even death (CDC, unpublished data); partial or complete susceptibility in 1-dose vaccine recipients as they become adults; the burden on public health agencies due to varicella outbreaks in highly vaccinated school settings, which have proven disruptive to society and costly to control; and the increased immunity and disease protection from a second dose. Overall, the 2-dose strategy still provides very high cost savings (>$0.9 billion from societal perspective).  (emphases added)
So the ACIP justifications for adding a second dose, used the consequences of their decision to recommend the first dose of varicella vaccine. These ingenious calculations created a bigger cost savings than their first round!
Here are quotes showing the CDC knew that using a one-vaccine regimen would result in serious problems:
The study confirmed what doctors widely knew — that the vaccine’s protection does not last long.
And with fewer natural cases of the disease going around, unvaccinated children or children in whom the first dose of the vaccine fails to work have been catching the highly contagious disease later in life, when the risk of severe complications is greater, they said.
“If you’re unvaccinated and you get it later in life, there’s a 20-times greater risk of dying compared to a child, and a 10 to 15 times greater chance of getting hospitalized,” said Jane Seward of the Centers for Disease Control and Prevention in Atlanta, who worked on the study.  (emphases added)
While a second shot was recommended, it’s not the final word either because:
No one knows how long the effects of a second shot will last, said the research team, led by Sandra Chaves of the CDC.
Which was probably not part of the cost benefit question – and neither is the next part, because sicker children cost more to treat, and take longer to recover:
And when vaccinated children were infected, they tended to be sicker, probably because they were older. (emphasis added).
“Children between the ages of 8 and 12 years who had been vaccinated 5 years or more previously were two times as likely to have moderate-to-severe breakthrough disease as were those who had been vaccinated less than 5 years previously,” the researchers wrote. 
Circulating viral infections (natural chickenpox) boosted vaccine immunity in the early days of the one shot program:
An assessment of the duration of protection afforded by one dose of the varicella vaccine administered to children under the age of 13 years between December 1991 and January 1993 showed an increase in the geometric mean titer of varicella IgG antibody during a 10-year follow-up period. The most likely explanation for this increase was an anamnestic immune response due to exposure to wild-type VZV, since varicella was still common during that period.
These data suggest a steady decline over a period of years in disease protection afforded by a single dose of the varicella vaccine in the context of diminished circulation of wild-type virus. In contrast, a case–control study showed a 13% decline in vaccine effectiveness during the first year of vaccination, followed by stable levels of protection from 2 to 8 years after vaccination.  (emphasis added)
However, with less virus circulation as more children are vaccinated, this natural “booster” dose doesn’t happen. Since older people gain protection against shingles (herpes zoster) from regularly circulating chickenpox, what added risks might the chickenpox vaccine create for the elderly? An increase in shingles cases, for one thing:
Zhou  provides a detailed breakdown of the costs and benefits of a routine two-dose varicella vaccination program:
Because of modeled predictions of an increase in herpes zoster among unvaccinated adults as a possible short- and medium-term effect of a varicella vaccination program and the described significant health burden due to herpes zoster, some researchers have argued for including these costs in economic analyses. In the short and medium term, this would be likely to make a varicella vaccination program much less cost effective. However, in the long term, as herpes zoster incidence declines to levels lower than currently experienced, models predict the net health savings from varicella vaccination to increase substantially. For this reason and because US surveillance data do not show any consistent pattern of an increase in herpes zoster attributable to the varicella vaccination program, we assumed that varicella vaccination was cost-neutral with respect to herpes zoster.  (emphases added)
This is a really convenient assumption. Considering the added cost of an increase in shingles, and of treating more serious chickenpox infections in older children, it would be really hard to justify any childhood vaccinations against chickenpox, much less a two shot schedule.
It’s important to note that the phrases “short and medium term” and “long term” highlighted above are left undefined.
The US began widespread vaccination with the varicella vaccine in 1995, after which the Mayo Clinic found an increase in the rate of shingles cases from January 1, 1996 to December 31, 2001. From page 1344:
The adjusted incidence rate increased from 3.2 per 1000 person-years for 1996 to 1997 to 4.1 for 2000 to 2001 (Figure 2). Extrapolated to the entire 2005 US population, the 2000 to 2001 incidence rate from Olmsted County translates into nearly one million new HZ cases every year. 
An Australian study on the ACIP decision to disregard zoster, because of three studies showing no increase, mentioned this:
However, another study that was cited, although finding a similar decrease in varicella in the Massachusetts population, showed a significant near doubling of HZ incidence. 
The Joint Committee on Vaccination and Immunisation (U.K.) decided against universal varicella vaccination after several meetings considering the costs and benefits between 2007 and 2009. In their report they commented:
… a significant number of break through infections are predicted with a one dose childhood schedule, it is predicted that both strategies could lead to an increase in herpes zoster incidence for the first 40 to 60 years following the introduction of a vaccination programme. This is because epidemiological evidence suggests that immunity in adulthood is boosted by the exposure to children infected by varicella zoster virus. Without this natural boosting, current levels of immunity in adulthood may no longer be maintained. Vaccinations against herpes zoster would only be expected to partly offset this increase, as the expected increase in herpes zoster incidence would occur predominantly in middle-aged adults too young to be targeted for herpes zoster vaccination. An increase in varicella infection in adulthood might also be expected. This would include women of childbearing age, potentially increasing the risk to unborn children or neonate should infections occur during pregnancy.  (emphases added)
They also explain:
Cost-effectiveness modelling indicates that a two-dose childhood vaccination programme or a combined childhood and adult vaccination programme could be cost-effective but only after 80-100+ years of vaccination at an assumed cost of vaccine. Before this time, the combined programme would be unlikely to be cost-effective and for the first 30-50 years of a programme would have a high probability of being cost ineffective. 
Anyone remember this statement, quoted above?
In the short and medium term, this would be likely to make a varicella vaccination program much less cost effective. However, in the long term, as herpes zoster incidence declines to levels lower than currently experienced, models predict the net health savings from varicella vaccination to increase substantially.  (emphasis added)
We noted above the lack of definitions of short, medium and long-term in this quote. Would the US taxpayers have been happy to hear that a public health program will start saving money somewhere between 50 to 80 years from now? Would Americans have been happy to know that the CDC cherry-picked the data to support their conclusion that varicella vaccination would not lead to an increase in herpes zoster?
One study done on the cost of treating herpes zoster, focused on deciding whether a vaccine against this illness would be cost-effective.
We estimated the sum of all costs for an episode of zoster (in 2006 U.S. dollars) to be $576 (range, $90 to $1061) if vaccinated and $538 (range, $84 to $991) if unvaccinated. 
In 2005, the U.S. Census Bureau reported that more than 49 million persons 60 years of age or older reside in the United States. The cost of a universal vaccination program could range from $2.6 billion to $24 billion depending on the cost per person vaccinated (32). Although our analyses show that about $1.3 billion might be saved by the reduction of herpes zoster cases at a vaccine cost of $50, we found few circumstances in which widespread vaccination would lead to cost savings. 
This study also lined up their numbers with a study done in the United Kingdom (which does not vaccinate against chickenpox) and found:
The incidence of herpes zoster in the vaccine group of the Shingles Prevention Study was 40% to 80% higher than that reported in the United Kingdom study. 
Conclusion: The varicella vaccination program in the US is not cost-effective and has never been cost-effective. The CDC came up with arbitrary numbers to justify the use of this vaccine, which later proved incorrect. A sensible option with regard to a chickenpox vaccine, is that it could be offered to adults who, due to the vaccine program, are shown by a titer test, to have no immunity to chickenpox….If they wish to have it…
Adults who have had natural chickenpox in the past, should be informed of the benefits of exposure to chickenpox infection as they get older, in order to prevent shingles, and encouraged to spend time whenever possible with children who are experiencing this normal childhood illness.
Parents and other caretakers should be educated on how to care for children undergoing chickenpox, especially the importance of avoiding fever reducing drugs during this illness. 
Everyone should cooperate in protecting the immune impaired population from exposure. As we have discovered with the chickenpox vaccine, even with high coverage, outbreaks continue to occur. Perhaps intelligent management of illness will provide protection to adults from shingles, and to the immune impaired from chickenpox.
 An Economic Analysis of the Universal Varicella Vaccination Program in the United States, Fangjun Zhou, Ismael R. Ortega-Sanchez, Dalya Guris, Abigail Shefer, Tracy Lieu, and Jane F. Seward, The Journal of Infectious Diseases, 197: S156-64, 2008. http://www.journals.uchicago.edu/doi/pdf/10.1086/522135
Effects of chickenpox vaccine fade over time: study, Gene Emery, Reuters, March 14, 2007 http://www.reuters.com/article/idUSN1429730720070314
 Loss of Vaccine-Induced Immunity to Varicella over Time, Sandra S. Chaves, Paul Gargiullo, John X. Zhang, Rachel Civen, Dalya Guris, Laurene Mascola, Jane F. Seward, The New England Journal of Medicine, 356(11): 1121-1129 (2007). http://www.nejm.org/doi/pdf/10.1056/NEJMoa064040
 A Population-Based Study of the Incidence and Complications Rates of Herpes Zoster Before Zoster Vaccine Introduction, Barbara P. Yawn, Patricia Saddier, Peter C. Wollan, Jennifer L. St. Sauvier, Marge J. Kurland, Lina S. Sy, Mayo Clinic Proceedings, 82 (11) 1341-1349, November 2007. http://www.mayoclinicproceedings.com/content/82/11/1341.full
 Evidence of Increasing Frequency of Herpes Zoster Management in Australian General Practice Since the Introduction of a Varicella Vaccine, Mark R. Nelson, Helena C Britt and Christopher M Harrison, The Medical Journal of Australia, 193 (2): 110-113, 2010. http://www.mja.com.au/public/issues/193_02_190710/nel10369_fm.html
 Joint Committee on Vaccination and Immunisation. Statement on Varicella and Herpes Zoster Vaccines. http://www.dh.gov.uk/prod_consum_dh/groups/dh_digitalassets/@dh/@ab/documents/digitalasset/dh_114908.pdf
 Cost-Effectiveness of a Vaccine To Prevent Herpes Zoster and Postherpetic Neuralgia in Older Adults, John Hornberger, and Katherine Robertus, Annals of Internal Medicine, 145, 317-325, 2006. http://www.annals.org/content/145/5/317.full.pdf+html
 Acetaminophen: more harm than good for chickenpox? Doran TF, De Angelis C, Baumgardner RA, Mellits ED. Journal of Pediatr. Jun;114(6):1045-8, 1989. http://www.ncbi.nlm.nih.gov/pubmed/2656959