Nov 02 2010

The Chicken Pox Story

Prior to 1995 about 95% of the US population would get chicken pox by age 18. It was essentially a rite of passage, and almost everyone had their pox scar to show for it. In 1995 a chicken pox vaccine was introduced, and about 60% of children receive the vaccine. This has dramatically decreased the rate of chicken pox, with some interesting results.

Some Background on Chicken Pox

Chicken pox is caused by the Varicella zoster virus (VZV), a member of the herpes family of viruses. It causes a primary infection which results in a day or two of fever and malaise followed by a week of a macular papular rash – pustules filled with fluid. In children the disease is commonly mild, but not without complications. According to a review by Dr. Lichenstein:

Varicella also accounts for significant morbidity (4000 hospitalizations per year) and mortality (50-100 deaths per year) in otherwise healthy children; moreover, the annual cost of chickenpox has been estimated at $400 million in medical costs and lost wages in the past.

In immunocompromised children, such as those with leukemia, mortality rates from varicella have ranged from 7-28%. The case-fatality rate in the general population is 6.7 case per 100,000.

In addition, once the primary infection is over the virus is not eradicated. It moves into the dorsal root ganglia (sensory nerve cells just outside the spinal cord) and becomes dormant. But it can be reactivated later in life, usually (but not necessarily) in times of physiological stress, and can cause shingles, or herpes zoster.

Shingles is a rash in the distribution of 1 to a few spinal nerves. It can be painful, and when the rash is oozing it is infectious and can cause chicken pox in those who are not immune. Also it can be complicated by a condition known as post-herpetic neuralgia – a burning type of nerve pain in the distribution of the rash. PHN can be very painful and very difficult to treat.

The burden of disease like chicken pox is also disproportionately born by those of low income. Imagine a household with 2-3 children, each suffering from chicken pox lasting about a week but with an incubation period of 2-3 weeks. The household can be sick for a month, with the children having to stay home from school. This can be a significant financial burden on working families.

Imagine also being a child with a chronic medical condition leading to immunocompromise. Every time there is a reported case of chicken pox in your school, school becomes a potentially fatal place.

In short, while chicken pox is a mild disease for most children, it comes with a significant burden of morbidity, mortality, pain and suffering, financial costs and lost productivity.

The Chicken Pox Vaccine

The current chicken pox vaccine is a live attenuated virus – essentially it works by giving a mild infection, usually subclinical (which means it causes few or no symptoms), but sufficient to provoke an immune response. A single dose vaccine is about 75% effective in preventing chicken pox. In the 25% that do get a breakthrough infection, the infection is mild with less morbidity and mortality. However such infections are still contagious, and so the single-dose vaccine does not prevent outbreaks. Further, the risk of breakthrough cases appears to increase over time. Effective immunity significantly decreases after about 10 years following a single dose.

For this reason the current recommendation is for a second booster injection with the vaccine, which increases antibody titers and reduces breakthrough infection by 2/3 (in one study from 7% to 2.2%).

Because Varicella zoster infection is a lifelong disease once contracted, concerns arose about unintended consequences from a chicken pox vaccine program: shifting of the average age of contraction to older individuals, and increases in shingles.

Chicken pox is a more serious illness in older children and adults. Therefore protecting children from chicken pox may result in acquiring the disease as an adult, with a resultant increase is morbidity. Further, the fact that chicken pox is so common means that older children and adults (prior to the vaccine) were routinely exposed to the virus, resulting in a periodic natural booster to immunity. By preventing outbreaks, these natural booster shots are reduced, resulting in waning antibody titers (even in those who had the full infection and not the vaccine).

This question has been studied. Since there are so many variables there is considerable uncertainty as to what the net effect of a vaccination program would be. However, epidemiological modeling has shown that the overall morbidity would likely decrease with a vaccine program. Reduction in total chicken pox cases would be partially offset by a shifting upward of the age of infection, but there would still be a net benefit.

Further, the reduction in outbreaks of chicken pox leading to reduced exposure and immunity in the older population would likely lead to an increase in shingles cases. However, this effect would be temporary (essentially a generation) and eventually shingles cases would be reduced as we get an older population that never had chicken pox (remember, shingles only occurs in those who previously had the chicken pox infection, not the vaccine).

Because of the nature of Varicella zoster creating an optimal vaccine program has some challenges, but these challenges are being studied carefully. At present the recommendations are for a two-dose vaccination schedule to produce the best results and longest immunity. There may be the need for a booster in older children or young adults to maintain immunity. Further there is now a vaccine for those over 50 to reduce the risk and severity of shingles.

Essentially, in order for the vaccine program to be most effective we may need to replace a lifetime of multiple exposures to the wild version of the virus with multiple vaccinations over one’s lifetime to maintain immunity.

Let the Crank Fest Begin

Because of the complexity of the chicken pox vaccine there is a lot to cherry pick from if one is interested in spreading fear and misinformation in order to scare the public off the vaccine. Don’t worry – Joseph Mercola is on the job.

He begins, as many anti-vaccinationists do, by downplaying the severity of the disease the vaccine is meant to prevent:

It is estimated there were about 3.7 million cases of chickenpox annually in the U.S. before 1995, resulting in an average of 100 deaths (50 children and 50 adults, most of whom were immunocompromised). This hardly represents a dire, life-threatening epidemic that requires mass vaccination of all children!

Of course, if you are one of the 100 people who die, that is quite a dire and life-threatening epidemic. But Mercola also omits all the other aspects of the total chicken pox burden that I outlined above.

As with all such questions, the bottom line is – what is the risk vs benefit of getting the vaccine. The evidence strongly suggests that the total benefit outweighs the total risk – but some of the risk/benefit is subjective, like the risk of pain, the loss of work and school time, or financial loss. People are free to decide for themselves if the risk/benefit is worth it, but that requires full and fair information, not Mercola’s dismissiveness.

Incidentally, Mercola in this article recommends honey for treating Herpes zoster, claiming it works better than “the drugs.” He cites a prior article he wrote which in turn cites two sources, both anecdotal and dealing with oral and genital herpes outbreaks, not zoster. So the evidence is very low grade and not even relevant. There is no data with honey and herpes zoster or, more importantly, post herpetic neuralgia.

Mercola goes on to discuss the same issues I discuss above, but with an anti-vaccine spin rather than a sober analysis. He cherry picks the data, and ignores those analyses which show a net benefit for the vaccine, even with these issues, and the offered solutions.

Conclusion

Chicken pox is far from the worst infectious disease that plagues humanity, but it does come with a significant burden of morbidity and mortality. We have the ability to reduce this burden with a rational vaccine program. Such a program has some interesting challenges, such as the consequences on long term immunity and the incidence of herpes zoster, but these are manageable.

The relevant issues require further monitoring and study, and optimal recommendations will likely be tweaked going forward.

Unfortunately, amidst this science-based conversation, there are anti-vaccine cranks who seem to be interested only in poisoning the well and spreading confusion.

Share

17 responses so far

17 Responses to “The Chicken Pox Story”

  1. ChrisHon 02 Nov 2010 at 2:10 pm

    Here I share our experience with chicken pox. While sorting through photos I found some of my then six month old daughter as she was recovering. I was shocked at the pox by her eyes and on her scalp. That whole month was a blur.

  2. Timmysonon 02 Nov 2010 at 2:29 pm

    You say that there would be a marginal benefit in terms of reduction in morbidity and mortality. What about cost effectiveness?

    Since for the vast majority of people, the only change will be a change in convenience and personal financial expenditure, rather than a matter of life and death, it seems that should be a consideration.

  3. Steven Novellaon 02 Nov 2010 at 3:21 pm

    Regarding cost effectiveness:

    Studies show (references below) that the vaccine is cost effective for high risk group even when only considering medical costs.

    They are cost effective for low risk groups when you consider the entire social burden of the illness (rather than just direct medical costs).

    This is a bit of a moving target, however, as recommendations are changing as new data comes in.

    http://www.ncbi.nlm.nih.gov/pubmed/18665775
    http://www.ncbi.nlm.nih.gov/pubmed/11803072
    http://www.ncbi.nlm.nih.gov/pubmed/9017774

  4. ChrisHon 02 Nov 2010 at 3:25 pm

    Yes, for a family with just one child, the two weeks can be a strain. For more than that, taking a full month can be a disaster. Especially if there is limited health insurance.

    Not everyone can afford to lose a month from work.

    Then there are the kids who have compromised immune systems and their siblings who need to stay away from school for the span of the outbreak, which is at least a month.

    Also, two weeks of a kid who is in constant itchy pain is no picnic. It is not something you really want a child to endure if you are at all compassionate. I could have lived without the sleep deprivation, washing sheets everyday, and constantly dealing with very sick and unhappy children for an entire month.

    Another thought on this paragraph:

    Further, the reduction in outbreaks of chicken pox leading to reduced exposure and immunity in the older population would likely lead to an increase in shingles cases. However, this effect would be temporary (essentially a generation) and eventually shingles cases would be reduced as we get an older population that never had chicken pox (remember, shingles only occurs in those who previously had the chicken pox infection, not the vaccine).

    The generation that is experiencing shingles at the moment is called “The Baby Boom” generation. The increase may because there are more of us!

    Also, there is shingles vaccine. Something my children may need when they are older, as they are part of the last major group to get chicken pox.

  5. invertedworldon 02 Nov 2010 at 4:38 pm

    My beautiful two year old son had a severe case of Chicken Pox and is now scarred on his face and body, maybe permanently. I live in the UK where the vaccine is not routinely provided, and I was not even aware that it had even been licensed and was even available until it was too late. My wife is expecting our second child and I will be having him vaccinated at the earliest opportunity.

  6. gammidgyon 02 Nov 2010 at 5:37 pm

    Steve, you don’t mention the risks associated with infection during pregancy. I read that lasting damage to the child is rare but potentially severe.

    http://www.nhs.uk/chq/Pages/1109.aspx?CategoryID=54&SubCategoryID=137

  7. Khym Chanuron 03 Nov 2010 at 4:46 am

    Remembering what it was like when I had the chicken pox, I sure wish the vaccine had been around when I was a kid.

  8. Calli Arcaleon 03 Nov 2010 at 10:42 am

    I wasn’t very sick when I had chickenpox, and luckily I had a stay-at-home mom to care for me. (And then for my brothers, who also caught it.) But I missed a week of school. You don’t get paid for school, of course, and if you’re in (US) public school, it’s not like you’re out any tuition. But you’re out two whole weeks of education, and that can never be replaced. Sure, in the end, it didn’t make a lot of difference; I was fortunate enough for my chickenpox to coincide with spring break, so part of my convalescence didn’t include any lost school time. But my brothers did lose two weeks. I don’t understand why people would casually dismiss that. What if it was the last two weeks of the school year? You’d miss finals. That’s nothing to sneeze at.

  9. HHCon 03 Nov 2010 at 2:06 pm

    Can you imagine a shingles outbreak at 50 related to childhood chickenpox infection? Does a red unpleasant-looking rash across the chest with a constant burning sensation interest you in useful medications like Valtrex? It doesn’t disappear readily, the rash lingers for more than a month.

  10. bachfiendon 03 Nov 2010 at 11:41 pm

    If I had chickenpox as a child, then it ‘must’ have been absolutely benign and mild, because I don’t remember having it.

    But I know that I had it, because at least 40 years later, after coming home after a run, I noticed that I had an ‘allergic’ rash under the chest-strap of a heart rate monitor, and then I noticed that it was just right sided exactly in the distribution of T4, and the penny dropped; shingles!, so I rushed off to have my diagnosis confirmed and have the specific antiviral medication prescribed.

    If you diagnose shingles early enough and get the treatment within 72 hours, the course of the illness is much reduced (I had a rash, and not much else).

    I’d donated blood several days earlier (and for some reason, that donation had to be discarded), but I was extremely popular with the Red Cross for several years afterwards, as I was harvested fortnightly for the specific anti-varicella antibodies (chickenpox can be very serious in the immune depressed).

  11. BillyJoe7on 04 Nov 2010 at 7:10 am

    “If you diagnose shingles early enough and get the treatment within 72 hours, the course of the illness is much reduced”

    Actually the benefits of treatment of Shingles with anti-viral agents is rather disappointing. If reduces the formation of new lesions by about one day and it does nothing to reduce the incidence and severity of post herpetic neuralgia and it does not prevent spread of the virus.
    It is also very expensive.

  12. Calli Arcaleon 04 Nov 2010 at 10:23 am

    So bachfiend may have just been lucky? That’s too bad; shingles can be a real bugger. A relative of mine had it a few years ago, and still has facial paralysis on one side. Since she has had no restoration of function or sensation, her doctor has warned her it is likely permanent. She’s just glad she didn’t get the neuralgia; that can be downright torturous.

  13. SimonWon 04 Nov 2010 at 4:48 pm

    Thanks Steve. I didn’t expect to learn much about vaccines from the current spate of articles, but this was excellent. As another UK citizen thinking of vaccinating my child for chickenpox this was very useful, I was always somewhat skeptical of arguments given against the vaccination and it looks like the science has moved on to prove them unfounded.

  14. SimonWon 04 Nov 2010 at 4:57 pm

    Latest UK position on chicken-pox vaccination.

    http://www.dh.gov.uk/prod_consum_dh/groups/dh_digitalassets/@dh/@ab/documents/digitalasset/dh_114908.pdf

  15. bachfiendon 04 Nov 2010 at 5:10 pm

    Perhaps I was lucky with my episode of shingles? Or perhaps the placebo effect is real?

    My doctor (actually a virologist in a tertiary medical centre) provided a lot of advice about symptomatic treatment for the intolerable itch and the unbearable pain… But it was very mild.

    Anecdotal evidence doesn’t count for much I know, but I started treatment within 10 hours (the pharmacy had to get the medication in from the supplier), which would be prompt compared to what happens in most clinical trials.

    Chickenpox immunisation was just about coming into Australia at the time, but it was fairly expensive and not covered with a subsidy from the government.

  16. Donna B.on 05 Nov 2010 at 5:00 pm

    (remember, shingles only occurs in those who previously had the chicken pox infection, not the vaccine)

    How do we know this? I’m not saying it’s not true…

  17. HHCon 05 Nov 2010 at 11:22 pm

    bachfiend, That’s not a placebo effect. Good to hear you got prompt treatment. I know of a person who walked around with the same problem while it oozed, itched, and was inflamed for a week. The medication was quite effective compared to nontreatment.

Trackback URI | Comments RSS

Leave a Reply

You must be logged in to post a comment.