Tracking varicella deaths: accuracy and completeness of death certificates and hospital discharge records, New York State, 1989-1995

Decline in Severe Varicella Disease During the United States Varicella Vaccination Program: Hospitalizations and Deaths, 1990-2019

To describe the impact of the US varicella vaccination program on severe varicella outcomes, we analyzed varicella hospitalizations using the National Inpatient Sample 1993-2019 and varicella deaths using the National Center for Health Statistics data 1990-2019. Over 25 years of vaccination program (1995-2019), varicella hospitalizations, and deaths declined 94% and 97%, respectively, among persons aged <50 years. Most of the decline (∼90%) occurred during the 1-dose period (through 2006/2007) by attaining and maintaining high vaccination coverage; additional declines occurred during the 2-dose period, especially in the age groups covered by the 2-dose recommendation. The greatest decline for both hospitalizations and deaths (97% and >99%, respectively) was among persons aged <20 years, born during the varicella vaccination program. In the <20 age group, varicella hospitalization has become a rare event, and varicella deaths have been practically eliminated in the United States. A total of >10 500 varicella hospitalizations and 100 varicella deaths are now prevented annually in the United States as a direct result of vaccination and reduction in varicella-zoster virus circulation.

Varicella Pneumonia: Case Report and Review of a Potentially Lethal Complication of a Common Disease

Varicella zoster virus causes varicella (chickenpox). It can be reactivated endogenously many years later to cause herpes zoster (shingles). Although varicella is usually a benign disease in healthy children, it resulted in over 11 000 hospitalizations and over 100 deaths every year, in all ages, in the United States. Morbidity was considerably worse in older teenagers and adults. Between 5% and 15% of cases of adult chickenpox will produce some form of pulmonary illness. Progression to pneumonia risk factors include pregnancy, age, smoking, chronic obstructive pulmonary disease, and immunosuppression. Typically, pulmonary symptoms occur 1 to 6 days after varicella zoster infection. They often include cough, fever, and dyspnea. Treatment is a 7-day course of intravenous acyclovir for varicella pneumonia. Early intervention may modify the course of this complication. This review illustrates practical features with a case of a 34-year-old female with severe varicella pneumonia. Despite the lack of significant past medical history and absence of immunosuppression, her pneumonia worsened and by using continuous positive airway pressure mask, intubation was avoided. More important, the radiographic progression of severe varicella pneumonia is shown. This highlights how a common disease of varicella can progress in an adult and manifest with significant organ malfunction.

Disseminated herpes zoster causing acute respiratory distress syndrome in an immunocompetent patient

Disseminated cutaneous varicella herpes zoster with visceral involvement is rare and seen almost exclusively in immunocompromised patients. We describe an unusual case of fulminant herpes zoster (HZ) in a healthy, immunocompetent 37-year-old woman. She initially presented to an urgent care centre with a classic HZ rash localised to her neck, and upper respiratory symptoms and was treated with prednisone and cephalexin. Within 1 week, the rash became diffuse and her clinical status rapidly deteriorated with development of severe acute respiratory distress syndrome. Varicella zoster infection was confirmed via skin biopsy, bronchial viral PCR and serology for varicella antibodies. She was successfully treated with intravenous acyclovir and aggressive supportive care. Though physicians readily recognise typical zoster infection, this case reminds clinicians that HZ infection can be fulminant and potentially life-threatening in younger, immunocompetent individuals. Early recognition and antiviral therapy is important to reduce morbidity and mortality.

Trends in varicella mortality in the United States: Data from vital statistics and the national surveillance system

This manuscript describes trends in US varicella mortality using national vital statistics system data for 2008-2011, the first years of the routine 2-dose varicella vaccination program, and characteristics of varicella deaths reported to CDC during 1996-2013. We obtained data on deaths with varicella as underlying or contributing cause from the 2008-2011 Mortality Multiple Cause-of Death records and calculated rates to compare with the prevaccine and mature 1-dose varicella vaccination program eras. We also reviewed available records of varicella deaths reported to CDC through the national varicella death surveillance. The annual average age-adjusted mortality rate for varicella as the underlying cause was 0.05 per million population during 2008-2011, an 87% reduction from the prevaccine years. Varicella deaths among persons aged <20 y declined by 99% in 2008-2011 compared with prevaccine years. There was a 70% decline in varicella mortality rates among those <20 y in 2008-2011 compared to 2005-2007. Among the 83 deaths reported to CDC during 1996-2013 classified as likely due to varicella, 24 (29%) were among immunocompromised individuals. Five were among persons previously vaccinated with 1 dose of varicella vaccine. In conclusion, although the US varicella vaccination program has significantly reduced varicella disease burden, there are still opportunities to prevent varicella and its associated morbidity and mortality through routine varicella vaccination, catch-up vaccination, and ensuring that household contacts of immunocompromised persons have evidence of immunity.

Herpes zoster-related deaths in the United States: validity of death certificates and mortality rates, 1979-2007

BACKGROUND

Herpes zoster (HZ) vaccine was recommended in the United States to reduce HZ-associated morbidity. Vaccination may reduce HZ-associated mortality, but no strategy exists to monitor mortality trends.

METHODS

We validated HZ coding on death certificates from California, using hospital records as the gold standard, and applied the results to national-level data to estimate HZ mortality.

RESULTS

In the validation phase of the study, among 40 available hospital records listing HZ as the underlying cause of death, HZ was the underlying cause for 21 (52.5%) and a contributing cause for 5 (12.5%). Among the 21 hospital records listing HZ as the underlying cause of death, the median age of decedents was 84 years (range, 50-99); 60% had no contraindications for HZ vaccination. Of the 37 available records listing HZ as a contributing cause of death, HZ was a contributing cause for 2 (5.4%) and the underlying cause for 6 (16.2%). Nationally, in the 7 years preceding the HZ vaccination program, the average annual number of deaths in which HZ was reported as the underlying cause of death was 149; however, based on our validation study, we estimate the true number was 78 (range, 31-118).

CONCLUSIONS

National death certificate data greatly overestimate deaths in which HZ is the underlying or contributing cause of death. The HZ vaccination program could prevent some HZ-related deaths, but the impact will be difficult to assess using national mortality data.

Safety of a second dose of varicella vaccine administered at 4 to 6 years of age in healthy children in Argentina

Varicela Biken [Live varicella Biken vaccine (strain Oka)] is an effective and safe vaccine for the prevention of varicella infection. Although the recommended schedule in all age groups (children, adolescents and adults) is a single dose, physicians in some countries follow the 2007 recommendation of the US Advisory Committee on Immunization Practices (ACIP) which recommends "implementation of a routine 2-dose varicella vaccination program for children, with the first dose administered at age 12--15 months and the second dose at age 4--6 years." ( 1) Therefore, cases can arise when two doses of Varicela Biken are given even though the ACIP guidelines are a response to the US epidemiological situation and for US licensed products based on the Oka/Merck and the Oka-RIT strains (Varicela Biken is not registered in US). The aim of this study is to ascertain the safety of a second dose of Varicela Biken in children who have been previously vaccinated with the same vaccine. In this study, children, 4-6 years of age who had been previously vaccinated with Varicela Biken, received a single 0.5 mL dose of live attenuated varicella virus vaccine containing at least 1000 Plaque Forming Units (PFU) attenuated live Varicella-zoster virus (Oka strain). Participants were monitored for 30 minutes after vaccination. Predefined injection site and systemic reactions were solicited during the subsequent seven days. Unsolicited injection site reactions and unsolicited systemic events were collected throughout the study. Any serious adverse events occurring throughout the study were reported to the sponsor's pharmacovigilance department. One hundred and twenty two children were recruited and all provided safety data. There were no immediate adverse events or injection site reactions. Forty three percent of participants reported injection site reactions and 22.1% reported systemic reactions on solicitation during the seven days after vaccination. During the 30 day monitoring period, 43 participants reported a total of 66 adverse events. Seven participants reported a total of eight unsolicited events that were assessed as related to the vaccine or where the relationship to vaccination was unknown. Five of these eight events were injection site reactions and all were mild, systemic reactions included mild rash (1 case) and fever (2 cases). There was a single serious adverse event that was not related to the study medication (subject was a passenger in a motor vehicle accident). A second dose of Varicela Biken was well tolerated and showed no significant safety issues in this population of previously vaccinated children.

Near elimination of varicella deaths in the US after implementation of the vaccination program

OBJECTIVE

Varicella has been preventable by vaccination in the United States since 1995. Previous studies reported a 66% decline in mortality rate during the first 6 years of the program. Since then, vaccination coverage has increased substantially. We updated the analysis of US varicella mortality for 2002-2007 and assessed the impact of the first 12 years of the US varicella vaccination program on varicella deaths.

METHODS

National data on deaths for which varicella was listed as an underlying or contributing cause were obtained from the Mortality Multiple Cause-of-Death records from the US National Center for Health Statistics. We calculated the age-adjusted and age-specific mortality rates for 2002-2007 and trends since the prevaccine years.

RESULTS

During the 12 years of the mostly 1-dose US varicella vaccination program, the annual average mortality rate for varicella listed as the underlying cause declined 88%, from 0.41 per million population in 1990-1994 to 0.05 per million population in 2005-2007. The decline occurred in all age groups, and there was an extremely high reduction among children and adolescents younger than 20 years (97%) and among subjects younger than 50 years overall (96%). In the last 6 years analyzed (2002-2007), a total of 3 deaths per age range were reported among children aged 1 to 4 and 5 to 9 years, compared with an annual average of 13 and 16 deaths, respectively, during the prevaccine years.

CONCLUSIONS

The impressive decline in varicella deaths can be directly attributed to successful implementation of the 1-dose vaccination program. With the current 2-dose program, there is potential that these most severe outcomes of a vaccine-preventable disease could be eliminated.

Varicella prevention in the United States: a review of successes and challenges

OBJECTIVE

In 1995, the United States was the first country to introduce a universal 1-dose childhood varicella vaccination program. In 2006, the US varicella vaccine policy was changed to a routine 2-dose childhood program, with catchup vaccination for older children. The objective of this review was to summarize the US experience with the 1-dose varicella vaccination program, present the evidence considered for the policy change, and outline future challenges of the program.

METHODS

We conducted a review of publications identified by searching PubMed for the terms "varicella," "varicella vaccine," and "herpes zoster." The search was limited to US publications except for herpes zoster; we reviewed all published literature on herpes zoster incidence.

RESULTS

A single dose of varicella vaccine was 80% to 85% effective in preventing disease of any severity and >95% effective in preventing severe varicella and had an excellent safety profile. The vaccination program reduced disease incidence by 57% to 90%, hospitalizations by 75% to 88%, deaths by >74%, and direct inpatient and outpatient medical expenditures by 74%. The decline of cases plateaued between 2003 and 2006, and outbreaks continued to occur, even among highly vaccinated school populations. Compared with children who received 1 dose, in 1 clinical trial, 2-dose vaccine recipients developed in a larger proportion antibody titers that were more likely to protect against breakthrough disease and had a 3.3-fold lower risk for breakthrough disease and higher vaccine efficacy. Two studies showed no increase in overall herpes zoster incidence, whereas 2 others showed an increase.

CONCLUSIONS

A decade of varicella prevention in the United States has resulted in a dramatic decline in disease; however, even with high vaccination coverage, the effectiveness of 1 dose of vaccine did not generate sufficient population immunity to prevent community transmission. A 2-dose varicella vaccine schedule, therefore, was recommended for children in 2006. Data are inconclusive regarding an effect of the varicella vaccination program on herpes zoster epidemiology.

Impact of varicella vaccination on health care outcomes in Ontario, Canada: effect of a publicly funded program?

Varicella vaccines have been available for private purchase in Canada since 1998. Ontario introduced publicly funded varicella vaccination in 2004. We assessed the effects of private availability of varicella vaccines and subsequent implementation of a publicly funded vaccination program on varicella-related hospitalizations, emergency department (ED) use, and visits to physicians' offices in Ontario. Rates of hospitalizations, ED use, and office visits decreased 53% (95% CI, 48-58%), 43% (95% CI, 41-44%), and 45% (95% CI, 44-45%) after publicly funded vaccination, compared to only 9% (95% CI, 4-14%), 23% (95% CI, 22-24%), and 29% (95% CI, 28-29%) after private availability. Varicella vaccination is effective at reducing varicella-related health care use, with benefits extending beyond those who receive the vaccine. Publicly funded vaccination programs may be more effective than private vaccine availability.

Varicella-related deaths in children and adolescents--Germany 2003-2004

AIM

Although varicella is acknowledged as a rare cause of death in children, there are few comprehensive data with respect to the clinical course leading to death.

METHODS

A nationwide, active surveillance was carried out in Germany for children up to age 17 years who were admitted to a paediatric hospital for varicella or associated complications, including deaths.

RESULTS

A total of 10 children with varicella-associated death were reported over period of 2 years, yielding a mortality rate of 0.4/1 000 000 children per year. Three deaths occurred in children diagnosed with acute lymphocytic leukaemia and disseminated varicella, two shortly after diagnosis of leukaemia and therefore not preventable, and one during remission with an untypical presentation. Two children died with a congenital varicella syndrome. There was no death in children with neonatal varicella. Four other cases were related to varicella pneumonia or septicaemia and one to myocarditis.

CONCLUSION

In a population with no general varicella vaccination programme, varicella accounted for a small but not negligible risk for death in immunocompetent and immunocompromised children. Together these data point to the importance of a thoroughly implemented, general varicella vaccination programme.

Varicella

Varicella-zoster virus, a herpesvirus, causes varicella (chickenpox) and, after endogenous reactivation, herpes zoster (shingles). Varicella, which is recognised by a characteristic vesicular rash, arises mainly in young children, although older individuals can be affected. In immunocompetent patients, symptoms are usually mild to moderate, but an uncomplicated severe case can have more than 1000 lesions and severe constitutional symptoms. Serious complications--including central nervous system involvement, pneumonia, secondary bacterial infections, and death--are sometimes seen. Varicella can be prevented by vaccination. Vaccine is about 80-85% effective against all disease and highly (more than 95%) effective in prevention of severe disease. In the USA, a routine childhood immunisation programme has reduced disease incidence, complications, hospital admissions, and deaths in children and in the general population, indicating strong herd immunity. Similar immunisation programmes have been adopted by some other countries, including Uruguay, Germany, Taiwan, Canada, and Australia, and are expected to be implemented more widely in future.

Varicella-related hospitalization and emergency department visit rates, before and after introduction of varicella vaccine, among white and black children in Hamilton County, Ohio

OBJECTIVE

The American Academy of Pediatrics recommended routine use of varicella vaccine in pediatric practice in 1995. We examined the impact of varicella immunization on population-based rates of pediatric varicella-related hospitalizations and emergency department (ED) visits in the years before and after introduction of varicella vaccine.

STUDY DESIGN

Discharge data for hospitalizations and ED encounters from 1990 through 2003 were queried for patients <20 years of age with varicella International Classification of Diseases, Ninth Revision, Clinical Modification codes (052.0-052.9) in any diagnostic position. Addresses were geocoded for identification of Hamilton County, Ohio, residents. Rates were calculated according to year, age, and race, with census estimates.

RESULTS

During the 14-year study period, there were 3983 incident varicella cases; 335 patients were hospitalized and 3833 were treated only in the ED. The rate of varicella-related hospitalizations decreased from 15.7 cases per 100,000 population to 5.5 cases per 100,000 population between the prevaccine period (1990-1995) and the postvaccine period (1996-2003); varicella-related ED use decreased from 178.2 cases per 100,000 population to 61.2 cases per 100,000 population. In the prevaccine period, hospitalization and ED visit rates were significantly higher for black children than for white children. In the postvaccine period, hospitalization rates did not differ according to race but ED visit rates remained significantly higher for black children, compared with white children.

CONCLUSIONS

Varicella-related hospitalization and ED visit rates decreased significantly for both white and black children in Hamilton County, Ohio, after the introduction of varicella vaccine, and the racial disparity found before licensure decreased after licensure.

The changing epidemiology of chickenpox in Alberta

BACKGROUND

Varicella vaccine was licensed in Canada in 1998. The province of Alberta introduced a universal publicly funded varicella vaccination program in 2001.

PURPOSE

To describe the epidemiology of non-fatal cases of chickenpox for which publicly funded health services were utilized for the period 1986-2002.

METHODS

We used the records of Alberta's universal, publicly funded health care insurance system to identify cases of chickenpox for the period 1986-2002. The earliest dated utilization of a health service for which there was an ICD9-CM code of 052.xx or an IC10-CA code of B01.xx was used as the date of illness onset. Denominators for rates were estimated using mid-year population estimates from the Alberta Health Care Insurance Registry. Age-specific rates were estimated for each year.

RESULTS

The crude incidence of chickenpox significantly declined over the period 1994-2002, most steeply after the year 2000. The incidence of chickenpox varied by age group and year and there was evidence of age-group-year interaction. Among those aged 5-19 years, chickenpox incidence began to decline prior to vaccine licensure in Canada. Among those aged less than one year and those aged 1-4 years, the incidence increased until 1999 when a decline began. Over the period 0.8% of cases were hospitalized.

CONCLUSION

Chickenpox rates began to decline prior to the introduction of the publicly funded vaccination program; however the declines in rates among the youngest age-groups are consistent with a vaccination program effect.

Decline in mortality due to varicella after implementation of varicella vaccination in the United States

BACKGROUND

Varicella disease has been preventable in the United States since 1995. Starting in 1999, active and passive surveillance data showed sharp decreases in varicella disease. We reviewed national death records to assess the effect of the vaccination program on mortality associated with varicella.

METHODS

Data on deaths for which varicella was listed as an underlying or contributing cause were obtained from National Center for Health Statistics Multiple Cause-of-Death Mortality Data for 1990 through 2001. We calculated the numbers and rates of death due to varicella according to age, sex, race, ethnic background, and birthplace.

RESULTS

The rate of death due to varicella fluctuated from 1990 through 1998 and then declined sharply. For the interval from 1990 through 1994, the average number of varicella-related deaths was 145 per year (varicella was listed as the underlying cause in 105 deaths and as a contributing cause in 40); it then declined to 66 per year during 1999 through 2001. For deaths for which varicella was listed as the underlying cause, age-adjusted mortality rates dropped by 66 percent, from an average of 0.41 death per 1 million population during 1990 through 1994 to 0.14 during 1999 through 2001 (P<0.001). This decline was observed in all age groups under 50 years, with the greatest reduction (92 percent) among children 1 to 4 years of age. In addition, by the period from 1999 through 2001, the average rates of mortality due to varicella among all racial and ethnic groups were below 0.15 per 1 million population, as compared with rates ranging from 0.37 per 1 million for whites to 0.66 per 1 million for other races in the period from 1990 through 1994.

CONCLUSIONS

The program of universal childhood vaccination against varicella in the United States has resulted in a sharp decline in the rate of death due to varicella.

Methods for capture-recapture analysis when cases lack personal identifiers

Methods for estimating the size of a closed population from a capture-recapture study require the availability of unique identifiers on each of two lists. These identifiers are used to identify the number of individuals appearing on both lists. When the number of individuals appearing on both lists cannot be determined with certainty from the data, matching between the lists is problematic. In this paper, we develop a weighted estimator to account for all possible matches between two lists. A bootstrap procedure is proposed for estimation. To illustrate the methods, we used two lists that recorded New York State (NYS) hospitalizations due to pertussis in 1996 to estimate the number of persons hospitalized for pertussis in NYS that year.

Varicella-related mortality in California, 1988-2000

BACKGROUND

Although surveillance for varicella in the United States has documented a reduction in cases since vaccine licensure in 1995, information is lacking on varicella-related mortality since vaccine introduction. This study identifies varicella-related mortality in California before and after vaccine introduction and assesses how high risk conditions and complications contributed to varicella deaths during this period.

METHODS

California death records mentioning varicella as either an underlying or contributing cause of death were selected from the 1988-2000 multiple cause-of-death files. Pre- and postvaccine periods were compared to assess differences in varicella mortality before and after vaccine introduction. Differences in varicella mortality by age, race/ethnicity and gender were also examined. ICD codes were used to identify high risk conditions and varicella-related complications.

RESULTS

A total of 228 varicella-related deaths were reported between 1988 and 2000 in California. Age-adjusted varicella mortality rates showed a downward trend during this period, dropping from a high of 0.97 per million in 1990 to a low of 0.22 per million in 1999. The average age-adjusted mortality rate declined from 0.67 per million prevaccine to 0.38 per million postvaccine. Compared with the prevaccine period, the average rate of decline in varicella mortality was greater after vaccine implementation. Infants had the highest mortality rate for the period. At least one immunocompromising condition was present in 38% of varicella-related deaths. Pneumonia was the most commonly reported complication.

CONCLUSIONS

Varicella-related mortality declined in California after vaccine implementation, but potentially preventable varicella-related deaths continue to occur.