For most people reading this, chickenpox was an almost unavoidable part of growing up. Within a few weeks of someone at school contracting the virus, it would have left a trail of blistered kids in its wake. The virus was so widespread in kids that 90% of adults were believed to be immune due to having contracted the illness when young.
Over the past two decades the school scene outlined above has disappeared though. The driver of the change is the Merck ($MRK) vaccine Varivax. Multiple studies have linked the vaccine--approved in the U.S. in 1995--with declines in the number of chickenpox cases and related hospitalizations. A long-term research project published in Pediatrics this week has added to the weight of evidence supporting the use of Varivax.
Researchers at the Kaiser Permanente Vaccine Study Center tracked 7,585 people who received Varivax in 1995 at age 2. Over the next 14 years, the researchers checked in every 6 months to see if any of the kids had caught chickenpox. In this cohort of children, the average incidence of chickenpox was 15.9 per 1,000 person-years. A typical incidence in the prevaccination era was up to 10-fold higher. Furthermore, those who did catch chickenpox only suffered from mild symptoms. The days of kids suffering from hundreds of lesions, needing hospitalization and, in some cases, dying, appear to be over.
A possible obstacle to this optimistic outlook is the unwillingness of some to vaccinate their kids against the virus. In 2011, the national vaccination rate among infants aged 19 to 35 months topped 90%, but a minority of parents oppose immunization, preferring to try to have their child become immune by contracting the virus. "Pox parties" and the swapping of candy from an infected child are reportedly used to deliberately spread the virus, and have been condemned by health experts.
Merck has cornered the market among parents who are willing to vaccinate their kids against the virus. Its two chickenpox vaccines--Varivax and ProQuad--are the only ones licensed in the U.S. Varivax generated sales of $846 million last year. Merck had expected the 2005 U.S. approval of ProQuad--a combined vaccine for measles, mumps, rubella and chickenpox--to further cement its stronghold. But the vaccine has been dogged by supply problems. These were resolved late last year, finally giving Merck the combined vaccine it long pursued.
When people get to the age when the chickenpox virus can manifest as shingles, Merck has them covered too. After also suffering years of supply problems, its shingles vaccine Zostavax is now available.
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