Dramatic Drop in Chickenpox Since Vaccination Program Instituted

MedicalResearch.com Interview with:

Jessica Leung, MPH and Rafael Harpaz, MD, MPH

Division of Viral Diseases,

National Center for Immunization and Respiratory Diseases (NCIRD)

Centers for Disease Control and Prevention (CDC)

MedicalResearch: What is the background for this study?

Authors’ Response: Prior to the introduction of varicella (chickenpox) vaccination in the U.S., there were millions of cases, tens of thousands of hospitalizations, and hundreds of deaths due to varicella. One-dose of varicella vaccination was recommended in 1995, and two-doses in 2006. Since 1995, there have been substantial declines in varicella disease. In a previously published paper by authors Zhou et al (JAMA. 2005 Aug 17;294(7):797-802), they found an 88% decrease in varicella-related hospitalizations and a 59% decrease in outpatient visits during 1994-2002, a period after the one-dose program began in the U.S. but before the two-dose program started.

We wanted to update the prior analyses with an additional 10 years of data to describe the impact of the varicella vaccination program during a period of high 1-dose coverage and increasing levels of 2-dose coverage. We looked at claims data during the 1994-2012 period using the Truven Health MarketScan® databases.

MedicalResearch: What are the main findings?



Authors’ Response: We found that varicella outpatient visits declined 84% in 2012 versus the pre-vaccination period (1994-1995), with a 60% decline during the 2-dose period (2006-2012). Varicella hospitalizations declined 93% in 2012 versus the pre-vaccination period, with a 38% decline during the 2-dose period. The proportion of varicella outpatient visits with laboratory testing increased from 6% in 2003 to 17% in 2012.

The largest declines in outpatient visits and hospitalizations from the pre-vaccination period to 2006 were seen in children and adolescents aged 1-19 years who are targeted for varicella vaccination. However, it is interesting to note that we found dramatic declines among age groups not targeted for vaccination, including infants aged <1 year, who are not recommended for vaccination, and adults, who are not often vaccinated. This is likely due to lower rates of circulating varicella disease because of high levels of varicella vaccine coverage. One important question raised about the varicella vaccination program is whether protection from vaccination might wane over time. Although this study was not designed to directly assess waning vaccine immunity, we did not find evidence that protection starts to weaken years and decades after vaccination.

MedicalResearch: What should clinicians and patients take away from your report?

Authors’ Response:



Rates of varicella are declining to very low levels with significant declines after 1-dose of varicella vaccine was recommended in 1995 and additional declines after 2-doses was recommended in 2006.

It will become increasingly important for clinicians to test suspect cases of varicella as 1) health care providers may become less familiar with varicella since rates of varicella are declining, and 2) there are increasing numbers of cases in vaccinated persons, which are difficult to diagnose clinically.

Highest declines were seen in children (aged 1-19) targeted for vaccination. However, there were dramatic declines also seen among age groups not targeted for vaccination, likely due to the reduction in circulating varicella from the vaccination program.

Although the study was not designed to directly assess waning immunity, we found no evidence that protection starts to weaken years and decades after vaccination. We saw an ongoing decrease in varicella rates in adolescents and young adults, some of whom may have been vaccinated almost 20 years ago.

MedicalResearch: What recommendations do you have for future research as a result of this study?

Authors’ Response: Public health professionals need to continue to

1) recommend vaccination of varicella and other vaccine-preventable diseases in order to maintain high vaccination rates and

2) evaluate the varicella vaccine program to make sure that the vaccine continues to work and the program continues to perform as we want it to.

Citation:

Jessica Leung and Rafael Harpaz. Impact of the Maturing Varicella Vaccination Program on Varicella and Related Outcomes in the United States: 1994–2012. Journal of the Pediatric Infectious Diseases Society. Published online 12 Aug 2015. doi: 10.1093/jpids/piv044

Available at: http://jpids.oxfordjournals.org/content/early/2015/08/05/jpids.piv044.abstract?sid=a743fdd8-1a9d-4c7e-8595-e9ffb72c072c

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Jessica Leung, MPH and Rafael Harpaz, MD, MPH (2015). Dramatic Drop in Chickenpox Since Vaccination Program Instituted MedicalResearch.com









