Methodological issues in design and analysis of a matched case-control study of a vaccine's effectiveness

Effectiveness of the varicella vaccine in the real world, a matched case-control study

BACKGROUND

Universal varicella vaccination has been introduced in many countries, but there are a number of important differences in their vaccination strategies. It is essential to establish a vaccination program that can maximize the benefits of varicella vaccine, but there is a lack of comprehensive research on the effectiveness of varicella vaccine in different vaccination status.

METHODS

Using data from population-based surveillance platforms we conducted a 1:2 matched case-control study. The cases were clinically diagnosed varicella with onset from 2017 to 2021, 1-14 years old in Chaoyang District, Beijing. The controls were matched according to date of birth (±1 month), sex and residence. The vaccination data of the subjects were obtained from the Childhood Immunization Information Management System in Beijing. Using conditional logistic regression models with or without interaction terms, we evaluated the effectiveness of varicella vaccine in different vaccination status.

RESULTS

A total of 2528 cases and 5056 controls were enrolled. This study found that whether the time since last vaccination was adjusted had a substantial effect on the comparing vaccine effectiveness (VE) between subgroups. After adjustment for the time since last vaccination, 1) the incremental VE of 2-dose was 49.6 % (95 % Confidence Interval [CI], 38.8-58.6) compared with 1-dose (93.9 % vs. 88.0 %); 2) Among children who received one dose, the risk of chickenpox in children vaccinated at 18-23 months was 1.382 (95 %CI, 1.084-1.762) times that in children vaccinated at 12-17 months. 3) the VE with less than one, two, and three year intervals is higher than that with six-year-intervals (P < 0.05), respectively.

CONCLUSIONS

When comparing VE between subgroups of different vaccination status, the time since last vaccination should be adjusted. The first dose of varicella vaccine should be given as early as the second year of life, and the second dose can improve vaccine effectiveness.

Bayesian Model Averaging to Account for Model Uncertainty in Estimates of a Vaccine's Effectiveness

Purpose

Vaccine effectiveness (VE) studies are often conducted after the introduction of new vaccines to ensure they provide protection in real-world settings. Control of confounding is often needed during the analyses, which is most efficiently done through multivariable modeling. When many confounders are being considered, it can be challenging to know which variables need to be included in the final model. We propose an intuitive Bayesian model averaging (BMA) framework for this task.

Patients and Methods

Data were used from a matched case-control study that aimed to assess the effectiveness of the Lyme vaccine post-licensure. Cases were residents of Connecticut, 15-70 years of age with confirmed Lyme disease. Up to 2 healthy controls were matched to each case subject by age. All participants were interviewed, and medical records were reviewed to ascertain immunization history and evaluate potential confounders. BMA was used to systematically search for potential models and calculate the weighted average VE estimate from the top subset of models. The performance of BMA was compared to three traditional single-best-model-selection methods: two-stage selection, stepwise elimination, and the leaps and bounds algorithm.

Results

The analysis included 358 cases and 554 matched controls. VE ranged between 56% and 73% and 95% confidence intervals crossed zero in <5% of all candidate models. Averaging across the top 15 models, the BMA VE was 69% (95% CI: 18-88%). The two-stage, stepwise, and leaps and bounds algorithm yielded VE of 71% (95% CI: 21-90%), 73% (95% CI: 26-90%), and 74% (95% CI: 27-91%), respectively.

Conclusion

This paper highlights how the BMA framework can be used to generate transparent and robust estimates of VE. The BMA-derived VE and confidence intervals were similar to those estimated using traditional methods. However, by incorporating model uncertainty into the parameter estimation, BMA can lend additional rigor and credibility to a well-designed study.

Assessment of Clinical Effectiveness of BNT162b2 COVID-19 Vaccine in US Adolescents

Importance

The emergence of the B.1.617.2 (Delta) variant of SARS-CoV-2 has led to increases in both infections and hospitalizations among adolescents. Little is known about the effectiveness of the BNT162b2 vaccine in adolescents in the general population, as opposed to a clinical trial population.

Objective

To estimate the effectiveness of the BNT162b2 vaccine in adolescents aged 12 to 18 years.

Design, Setting, and Participants

This was a matched case-control study among adolescents (aged 12-18 years) who had results from a SARS-CoV-2 reverse transcription-polymerase chain reaction (RT-PCR) test. Immunization histories, relevant clinical data, and RT-PCR test results were obtained from the Yale New Haven Health System's medical records between June 1, 2021, and August 15, 2021, when the Delta variant caused 92% of infections in Connecticut. Case participants were defined as adolescents who had a positive test result and an associated medical encounter. Control participants were defined as those who had a negative test result and were matched to a case participant by age, county of residence, and date of testing.

Exposures

Adolescents were defined as fully immunized if they had received 2 doses of vaccine at least 14 days before focal time.

Main Outcomes and Measures

The primary outcome measured was SARS-CoV-2 infection confirmed by RT-PCR. The vaccine's effectiveness (VE) was estimated using matched odds ratios from conditional logistic regression models. Secondary measures included estimated VE by clinical symptoms, number of vaccine doses received, and elapsed time from immunization.

Results

A total of 6901 adolescents were tested for SARS-CoV-2. The final sample comprised 186 case participants and 356 matched control participants. The median age was 14 (IQR, 13-16) years, 262 (48%) identified as female, 81 (15%) as Black, 82 (15%) as Hispanic, and 297 (55%) as White. Overall, 134 (25%) were fully immunized (case participants, 10 [5%]; control participants, 124 [35%]). The median time between immunization and the SARS-CoV-2 test was 62 days (range, 17-129 days). Within 4 months of receiving 2 doses, VE against any infection was estimated to be 91% (95% CI, 80%-96%); against asymptomatic infection, 85% (95% CI, 57%-95%). Effectiveness after a single dose was estimated to be 74% (95% CI, 18%-92%).

Conclusions and Relevance

In this retrospective case-control study of US adolescents, 2 doses of BNT162b2 vaccine appeared to provide excellent protection for at least 4 months after immunization against both symptomatic and asymptomatic SARS-CoV-2 infections.

Rotavirus Epidemiology and Monovalent Rotavirus Vaccine Effectiveness in Australia: 2010-2017

BACKGROUND

Rotavirus vaccine has been funded for infants under the Australian National Immunisation Program since 2007, with Rotarix vaccine used in New South Wales, Australia, from that time. In 2017, New South Wales experienced a large outbreak of rotavirus gastroenteritis. We examined epidemiology, genotypic profiles, and vaccine effectiveness (VE) among cases.

METHODS

Laboratory-confirmed cases of rotavirus notified in New South Wales between January 1, 2010 and December 31, 2017 were analyzed. VE was estimated in children via a case-control analysis. Specimens from a sample of hospitalized case patients were genotyped and analyzed.

RESULTS

In 2017, 2319 rotavirus cases were reported, representing a 3.1-fold increase on the 2016 notification rate. The highest rate was among children aged <2 years. For notified cases in 2017, 2-dose VE estimates were 88.4%, 83.7%, and 78.7% in those aged 6 to 11 months, 1 to 3 years, and 4 to 9 years, respectively. VE was significantly reduced from 89.5% within 1 year of vaccination to 77.0% at 5 to 10 years postvaccination. Equinelike G3P[8] (48%) and G8P[8] (23%) were identified as the most common genotypes in case patients aged ≥6 months.

CONCLUSIONS

Rotarix is highly effective at preventing laboratory-confirmed rotavirus in Australia, especially in infants aged 6 to 11 months. Reduced VE in older age groups and over time suggests waning protection, possibly related to the absence of subclinical immune boosting from continuously circulating virus. G8 genotypes have not been common in Australia, and their emergence, along with equinelike G3P[8], may be related to vaccine-induced selective pressure; however, further strain-specific VE studies are needed.

Single-dose varicella vaccine effectiveness in Brazil: A case-control study

BACKGROUND

Varicella vaccine was introduced into the Brazilian Immunization Program in October 2013, as a single-dose schedule administered at 15 months of age. Its effectiveness had not yet been assessed in the country.

METHODS

A matched case-control study was carried out in São Paulo and Goiânia (Southeast and Midwest regions, respectively), Brazil. Suspected cases, were identified through a prospective surveillance established in the study sites. All cases had specimens from skin lesion collected for molecular laboratory testing. Cases were confirmed by either clinical or PCR of skin lesions and classified as mild, moderate, and severe disease. Two neighborhood controls were selected for each case. Cases and controls were aged 15-32 months and interviewed at home. Evidence of prior vaccination was obtained from vaccination cards. Univariate and multivariate logistic regression models were used, and odds ratio and its respective 95% confidence intervals were estimated. Vaccine effectiveness was estimated by comparing de odds of having received varicella vaccine among cases and controls.

RESULTS

A total of 168 cases and 301 controls were enrolled. Moderate and severe illness, was found in 33.3% and 9.9% of the cases. Effectiveness of a single dose varicella vaccine was 86% (95%CI 72-92%) against disease of any severity and 93% (95%CI 82-97%) against moderate and severe disease. Out of 168 cases, 81.8% had positive PCR results for wild-type strains, and 22.0% were breakthrough varicella cases. Breakthrough cases were milder compared to non-breakthrough cases (p < .001).

CONCLUSIONS

Effectiveness of single dose varicella vaccine in Brazil is comparable to that in other countries where breakthrough varicella cases have also been found to occur. The goal of the varicella vaccination program, along with disease burden and affordability should be taken into consideration when considering the adoption of a second dose of varicella vaccine into national immunization programs.

Effectiveness of Varicella Vaccination Program in Preventing Laboratory-Confirmed Cases in Children in Seoul, Korea

A universal one-dose varicella vaccination program was introduced in 2005 in Republic of Korea. However, the incidence of varicella in Korea has tripled over the last decade. We conducted a community based 1:1 matched case-control study to assess the effectiveness of one MAV strain-based vaccine and three Oka strain-based vaccines licensed for use in Korea. All cases were children in Seoul, Korea with varicella who were reported to the National Notifiable Disease Surveillance System in Seoul during 2013. The controls were age-matched children with mumps or scarlet fever but no history of varicella. We included 537 cases and 537 controls. The overall effectiveness of one dose of varicella vaccination was 13% (95% confidence interval [CI], -17.3-35.6). Of the four licensed varicella vaccines, only one was highly effective (88.9%; 95% CI, 52.1-97.4). The vaccine effectiveness for the other vaccines were 71.4% (95% CI, -37.5-94.1), -5% (95% CI, -61.9-31.9), and -100% (95% CI, -700-50.0). The overall effectiveness of vaccination was 75.8% (95% CI, 22.8-92.4) in the first year after vaccination and decreased thereafter; the effectiveness became -7.2% (95% CI, -130.9-59.2) in the fourth year after vaccination. Further studies are warranted to investigate reduced effectiveness of varicella vaccines in Korea.

Varicella Vaccine Effectiveness in Preventing Community Transmission in the 2-Dose Era

OBJECTIVES

We examined overall and incremental effectiveness of 2-dose varicella vaccination in preventing community transmission of varicella among children aged 4 to 18 years in 2 active surveillance sites. One-dose varicella vaccine effectiveness (VE) was examined in those aged 1 to 18 years.

METHODS

From May 2009 through June 2011, varicella cases identified during active surveillance in Antelope Valley, CA and Philadelphia, PA were enrolled into a matched case-control study. Matched controls within 2 years of the patient's age were selected from immunization registries. A standardized questionnaire was administered to participants' parents, and varicella vaccination history was obtained from health care provider, immunization registry, or parent records. We used conditional logistic regression to estimate varicella VE against clinically diagnosed and laboratory-confirmed varicella.

RESULTS

A total of 125 clinically diagnosed varicella cases and 408 matched controls were enrolled. Twenty-nine cases were laboratory confirmed. One-dose VE (1-dose versus unvaccinated) was 75.6% (95% confidence interval [CI], 38.7%-90.3%) in preventing any clinically diagnosed varicella and 78.1% (95% CI, 12.7%-94.5%) against moderate or severe, clinically diagnosed disease (≥50 lesions). Among subjects aged ≥4 years, 2-dose VE (2-dose versus unvaccinated) was 93.6% (95% CI, 75.6%-98.3%) against any varicella and 97.9% (95% CI, 83.0%-99.7%) against moderate or severe varicella. Incremental effectiveness (2-dose versus 1-dose) was 87.5% against clinically diagnosed varicella and 97.3% against laboratory-confirmed varicella.

CONCLUSIONS

Two-dose varicella vaccination offered better protection against varicella from community transmission among school-aged children compared with 1-dose vaccination.

Estimating time-varying exposure-outcome associations using case-control data: logistic and case-cohort analyses

BACKGROUND

Traditional analyses of standard case-control studies using logistic regression do not allow estimation of time-varying associations between exposures and the outcome. We present two approaches which allow this. The motivation is a study of vaccine efficacy as a function of time since vaccination.

METHODS

Our first approach is to estimate time-varying exposure-outcome associations by fitting a series of logistic regressions within successive time periods, reusing controls across periods. Our second approach treats the case-control sample as a case-cohort study, with the controls forming the subcohort. In the case-cohort analysis, controls contribute information at all times they are at risk. Extensions allow left truncation, frequency matching and, using the case-cohort analysis, time-varying exposures. Simulations are used to investigate the methods.

RESULTS

The simulation results show that both methods give correct estimates of time-varying effects of exposures using standard case-control data. Using the logistic approach there are efficiency gains by reusing controls over time and care should be taken over the definition of controls within time periods. However, using the case-cohort analysis there is no ambiguity over the definition of controls. The performance of the two analyses is very similar when controls are used most efficiently under the logistic approach.

CONCLUSIONS

Using our methods, case-control studies can be used to estimate time-varying exposure-outcome associations where they may not previously have been considered. The case-cohort analysis has several advantages, including that it allows estimation of time-varying associations as a continuous function of time, while the logistic regression approach is restricted to assuming a step function form for the time-varying association.

Two-dose varicella vaccine effectiveness and rash severity in outbreaks of varicella among public school students

BACKGROUND

Universal 2-dose varicella vaccination was recommended in 2006 to further reduce varicella disease burden. This study examined 2-dose varicella vaccine effectiveness (VE) and rash severity in the setting of school-associated varicella outbreaks.

METHODS

A case control study was conducted from January 2010 to May 2011 in all West Virginia public schools. Clinically diagnosed cases from varicella outbreaks were matched with classmate controls. Vaccination information was collected from school, health department and healthcare provider immunization information systems.

RESULTS

Among the 133 cases and 365 controls enrolled, VE against all varicella was 83.2% [95% confidence interval (CI): 69.2%-90.8%] for 1-dose of varicella vaccine and 93.9% (95% CI: 86.9%-97.1%) for 2-dose; the incremental VE (2-dose vs. 1-dose) was 63.6% (95% CI: 32.6%-80.3%). In preventing moderate/severe varicella, 1-dose varicella vaccine was 88.2% (95% CI: 72.7%- 94.9%) effective, and 2-dose vaccination was 97.5% (95% CI: 91.6%-99.2%) effective, with the incremental VE of 78.6% (95% CI: 40.9%-92.3%). One-dose VE declined along with time since vaccination (VE = 93.0%, 88.0% and 81.8% in <5, 5-9 and ≥ 10 years after vaccination, P = 0.001 for trend). Both 1- and 2-dose breakthrough cases had milder rash than unvaccinated cases (<50 lesion: 24.6%, 49.1% and 70.0% in unvaccinated, 1-dose and 2-dose cases, P < 0.001), and no severe disease was found in 2-dose cases.

CONCLUSIONS

Two-dose varicella vaccination is highly effective and confers higher protection than a 1-dose regimen. High 2-dose varicella vaccination coverage should maximize the benefits of the varicella vaccination program and further reduce varicella disease burden in the United States.

Asthma status and waning of measles antibody concentrations after measles immunization

BACKGROUND

Asthmatics have increased risks of common and serious microbial infections including vaccine preventable diseases. Little is known about whether asthma influences waning of humoral immunity. We assessed whether asthma status influences waning of anti-measles virus antibody concentrations over time.

METHODS

The study used a cross-sectional study cohort of healthy children who had been immunized with 1 dose of MMR-II at age approximately 15 months. Between 5 and 12 years of age, measles vaccine virus-specific antibody (IgG) values were measured by enzyme immunoassay and considered seropositive if the enzyme immunoassay index unit was ≥ 1. The medical records were reviewed to determine asthma status during the first 18 years of life by applying predetermined criteria for asthma. A least squares regression model was used to evaluate the effect of asthma status on the relationship between measles antibody titer and time elapsed between the initial measles vaccination and measurement of measles antibody concentrations.

RESULTS

Of the 838 eligible children, 281 (34%) met criteria for asthma. Measles antibody waned over time (r = -0.19, P < 0.001), specifically more rapidly in asthmatics (r = -0.30, P < 0.001, a decrease of -0.114 unit per year) than non-asthmatics (r = -0.13, P = 0.002, a decrease of -0.046 unit per year; P value for interaction = 0.010). This differential waning rate resulted in a lower mean (SD) measles antibody concentration [1.42 (0.67) vs. 1.67 (0.69), P = 0.008] and lower seropositivity rate (73% vs. 84%, P = 0.038) in asthmatics than non-asthmatics starting around 9.3 years after the initial measles vaccination.

CONCLUSION

Asthma status is associated with waning kinetics of measles antibody among children.

Biomarker discovery study design for type 1 diabetes in The Environmental Determinants of Diabetes in the Young (TEDDY) study

AIMS

The Environmental Determinants of Diabetes in the Young planned biomarker discovery studies on longitudinal samples for persistent confirmed islet cell autoantibodies and type 1 diabetes using dietary biomarkers, metabolomics, microbiome/viral metagenomics and gene expression.

METHODS

This article describes the details of planning The Environmental Determinants of Diabetes in the Young biomarker discovery studies using a nested case-control design that was chosen as an alternative to the full cohort analysis. In the frame of a nested case-control design, it guides the choice of matching factors, selection of controls, preparation of external quality control samples and reduction of batch effects along with proper sample allocation.

RESULTS AND CONCLUSION

Our design is to reduce potential bias and retain study power while reducing the costs by limiting the numbers of samples requiring laboratory analyses. It also covers two primary end points (the occurrence of diabetes-related autoantibodies and the diagnosis of type 1 diabetes). The resulting list of case-control matched samples for each laboratory was augmented with external quality control samples.

The effectiveness of varicella vaccination in children in Germany: a case-control study

BACKGROUND

Effectiveness of 1 dose of varicella vaccination was estimated to be 85-88% against clinical varicella of any severity in case-control studies in non-European countries, but lower effectiveness has been demonstrated in outbreaks.

METHODS

A prospective, age- and practice-matched case-control study was conducted in Germany to assess the effectiveness of 1 dose of OKA/GSK varicella vaccine (derived from the OKA strain, a Japanese clinical isolate) and of any varicella vaccine (including OKA/GSK, OKA/Merck and MMR-OKA/GSK) against polymerase chain reaction (PCR)-confirmed varicella under conditions of routine use.

RESULTS

The cohort included 432 PCR-confirmed cases and 432 matched controls (1-7 years old). Varicella vaccination was reported for 13.2% (57/432) of cases and 45.1% (195/432) of controls. Median time since vaccination was 28 and 25 months, respectively. Vaccinated cases experienced milder disease (P < 0.0001) and shorter duration of disease (P = 0.004) compared with unvaccinated cases. After adjusting for gender and school/day-care attendance, vaccine effectiveness of 1 dose of OKA/GSK against PCR-confirmed varicella of any severity was 71.5% (95% confidence interval [CI]: 49.1-84.0) and 94.7% (95% CI: 77.8-98.7) against PCR-confirmed moderate or severe varicella. Adjusted effectiveness for any varicella vaccine was 86.4% (95% CI: 77.3-91.8) against any severity and 97.7% (95% CI: 90.5-99.4) against moderate or severe varicella.

CONCLUSIONS

One dose of varicella vaccine provided high protection against moderate and severe varicella disease for a period of up to 5 years after vaccination. However, further effectiveness data are needed to assess long-term protection.

Effectiveness of one dose of mumps vaccine against clinically diagnosed mumps in Guangzhou, China, 2006-2012

Although mumps-containing vaccines were introduced in China in 1990s, mumps continues to be a public health concern due to the lack of decline in reported mumps cases. To assess the mumps vaccine effectiveness (VE) in Guangzhou, China, we performed a 1:1 matched case-control study. Among children in Guangzhou aged 8 mo to 12 y during 2006 to 2012, we matched one healthy child to each child with clinically diagnosed mumps. Cases with clinically diagnosed mumps were identified from surveillance sites system and healthy controls were randomly sampled from the Children's Expanded Programmed Immunization Administrative Computerized System in Guangzhou. Conditional logistic regression was used to calculate VE. We analyzed the vaccination information for 1983 mumps case subjects and 1983 matched controls and found that the overall VE for 1 dose of mumps vaccine, irrespective of the manufacture, was 53.6% (95% confidence interval [CI], 41.0-63.5%) to children aged 8 mo to 12 y. This post-marketing mumps VE study found that immunization with one dose of the mumps vaccine confers partial protection against mumps disease. Evaluation of the VE for the current mumps vaccines, introduction of a second dose of mumps vaccine, and assessment of modifications to childhood immunization schedules is essential.

Single-dose varicella vaccine effectiveness in school settings in China

BACKGROUND

Varicella vaccine has been available in the private sector in China for a decade as a single-dose regimen, but varicella vaccine effectiveness (VE) has not been fully examined in school settings yet.

METHODS

A matched case-control study was carried out in elementary schools and daycares in Tai'an prefecture, Shandong province, China. Clinical diagnosis of varicella and breakthrough disease was used for this study. Four controls were randomly selected from classmates; two from classmates of the case and two from another class of the same grade without cases. Vaccination status, date of vaccination, and vaccine product received if vaccinated were collected from home and clinic immunization records. Vaccination status of all students in schools/daycares with varicella cases from home immunization records or parental recall was used to calculate vaccination coverage.

RESULTS

The overall varicella VE was 83.4% (95% confidence interval 71.4-90.3%). Receipt of varicella vaccine five years or more years before the outbreak was significantly associated with breakthrough varicella (odds ratio=4.7, P<0.001), while age at vaccination (<15 vs. ≥15 months) was not (odds ratio=1.5, P=0.62). Varicella vaccination coverage was 41% with substantial variation across schools (range of 0-93.8%).

CONCLUSIONS

Single-dose varicella vaccine is highly effective in school settings. Maintaining limited vaccination coverage might shift varicella disease burden to older individuals, who are more prone to develop severe outcomes if varicella occurs.

Effectiveness of seasonal influenza vaccine against clinically diagnosed influenza over 2 consecutive seasons in children in Guangzhou, China: a matched case-control study

Influenza vaccine has to be reformulated each year due to the ever-changing antigenicity of the influenza virus. However, few post-licensure studies of influenza vaccine are available in China. We aimed to measure the effectiveness of seasonal influenza vaccine during 2 consecutive seasons. Among children in Guangzhou aged 6 to 59 mo in 2010-2012, we matched each child with clinically diagnosed influenza to 3 healthy children. Cases with clinically diagnosed influenza were identified from surveillance system. Healthy controls were randomly sampled from the Children's Expanded Programmed Immunization Administrative Computerized System. Conditional logistic regression was used to calculate vaccine effectiveness (VE). A total of 275 matched sets of subjects were included. VE levels against clinically diagnosed influenza for both seasons combined was 47.4% [95% confidence interval (CI), 8.5-69.8%] for full vaccination for children aged 6-35 mo, 33.6% (95% CI, 5.4-53.5%) for any vaccination for children aged 6-59 mo, respectively. VE by time since vaccination for any vaccination was 34.6% (95% CI, 4.7-55.2%) in 0-5 mo, and no protection was observed in 6-11 mo. Annual, full and timely vaccination should be encouraged for children.

Effectiveness of the monovalent G1P[8] human rotavirus vaccine against hospitalization for severe G2P[4] rotavirus gastroenteritis in Belém, Brazil

BACKGROUND

Brazil initiated universal immunization of infants with the G1P[8] human rotavirus (RV) vaccine in March 2006. This study evaluated vaccine effectiveness (VE) against severe rotavirus gastroenteritis (RVGE) hospitalizations.

METHODS

Matched case-control study conducted at 4 hospitals in Belém from May 2008 to May 2009. Cases were children hospitalized with RVGE age-eligible to have received 2 doses of the human RV vaccine (≥ 12 weeks of age and born after March 6, 2006). For each case, 1 neighborhood and 1 hospital control without gastroenteritis was selected, matching by birth date (± 8 and ± 6 weeks, respectively). Matched odds ratio of 2-dose RV vaccination in cases versus controls was used to estimate VE (1 - odds ratio × 100%).

RESULTS

Of 538 RVGE cases, 507 hospital controls and 346 neighborhood controls included, 54%, 61%, and 74% had received both RV vaccine doses. VE against RVGE hospitalization was 75.8% (95% confidence interval [CI]: 58.1-86.0) using neighborhood controls and 40.0% (95% CI: 14.2-58.1) using hospital controls. VE in children 3 to 11 months and ≥ 12 months of age was 95.7% (95% CI: 67.8-99.4) and 65.1% (95% CI: 37.2-80.6) using neighborhood controls, and 55.6% (95% CI: 12.3-77.5) and 32.1% (95% CI: -3.7-55.5) using hospital controls. G2P[4] accounted for 82.0% of RVGE hospitalizations. G2P[4]-specific VE was 75.4% (95% CI: 56.7-86.0) using neighborhood controls and 38.9% (95% CI: 11.1-58.0) using hospital controls.

CONCLUSIONS

Although fully heterotypic G2P[4] was the predominant RV strain, good VE was demonstrated. VE was highest in children aged 3 to 11 months. However, protection in children ≥ 12 months of age, important for optimal public health impact, was significantly sustained based on estimates obtained using neighborhood controls.

Influenza vaccine given to pregnant women reduces hospitalization due to influenza in their infants

BACKGROUND

Infants aged <12 months are at high risk of hospitalization for influenza. Influenza vaccine is recommended for pregnant women and for most children; however, no vaccine is approved for infants aged <6 months. Effective approaches are needed to protect this vulnerable population. Vaccination of women during pregnancy may protect the infant through transfer of antibodies from the mother. Few studies have examined the effectiveness of this strategy, and those studies produced mixed results.

METHODS

In a matched case-control study, case patients were infants aged <12 months admitted to a large urban hospital in the northeastern United States because of laboratory-confirmed influenza from 2000 to 2009. For each case, we enrolled 1 or 2 control subjects who were infants who tested negative for influenza and matched cases by date of birth and date of hospitalization (within 4 weeks). Vaccine effectiveness was calculated on the basis of matched odds ratios and was adjusted for confounding.

RESULTS

The mothers of 2 (2.2%) of 91 case subjects and 31 (19.9%) of 156 control subjects aged <6 months, and 1 (4.6%) of 22 case subjects and 2 (5.6%) of 36 control subjects aged ≥6 months, had received influenza vaccine during pregnancy. The effectiveness of influenza vaccine given to mothers during pregnancy in preventing hospitalization among their infants, adjusted for potential confounders, was 91.5% (95% confidence interval [CI], 61.7%-98.1%; P = .001) for infants aged <6 months. The unadjusted effectiveness was 90.7% (95% CI, 59.9%-97.8%; P = .001).

CONCLUSIONS

Influenza vaccine given to pregnant women is 91.5% effective in preventing hospitalization of their infants for influenza in the first 6 months of life.

Effectiveness of rotavirus vaccine in preventing hospitalization due to rotavirus gastroenteritis in young children in Connecticut, USA

Rotavirus vaccine was recommended for use in US infants to prevent rotavirus gastroenteritis (RGE) in February 2006. This matched case control study assessed the effectiveness of rotavirus vaccine in preventing hospitalization of young. Cases were vaccine-eligible children 8 weeks-3 years of age, hospitalized due to laboratory-confirmed RGE. Cases (n=42) were matched to 2 control groups: (a) hospitalized controls (n=80): children hospitalized for reasons other than RGE, matched to the cases by age and time of presentation and (b) community controls (n=73): non-hospitalized children matched by age and medical practice. Adjusted vaccine effectiveness against hospitalization with RGE in vaccine eligible children receiving at least one dose of vaccine was 94.3% (95% C.I.: 55.4%-99.3%; p=0.006) for hospitalized controls and 96.9% (95% C.I.: 59.4%-99.8%; p=0.008) for community controls.

The effectiveness of varicella vaccine in China

BACKGROUND

The attenuated live varicella vaccine had been shown to be effective in preventing varicella and reducing the disease burden in the United States. However, little work has been done on investigating vaccine effectiveness in China where 3 varicella vaccines are available. Although the vaccines contain the same strain of virus, the vaccines licensed in China were from manufacturers different from the one licensed in the United States. We conducted a matched case-control study to assess the effectiveness of the 3 varicella vaccines in use in China.

METHODS

In 2005, we enrolled 1000 cases from Guangzhou, China and 1000 controls matched by age and place of residence. The cases were children clinically diagnosed with acute onset of a diffuse maculopapulovesicular rash without other apparent cause. We interviewed the legal guardians of the participants for demographic information and disease history after obtaining informed consent. We collected information on vaccination status from electronic vaccination records.

RESULTS

The 3 varicella vaccines in China (Varilrix from GlaxoSmithKline, Changchun and Shanghai from Changchun and Shanghai Institutes of Biologic Products, respectively) had similar effectiveness: Varilrix 86.4% (95% confidence interval [CI]: 72.6, 93.2), Changchun 79.5% (95% CI: 58.1, 90.0), and Shanghai 92.6% (95% CI: 68.9, 98.2). Vaccine effectiveness was higher during the first year after vaccination than during the subsequent 5 years, but the differences did not reach statistical significance.

CONCLUSIONS

The varicella vaccines in China are highly effective in preventing clinical varicella. Further studies on laboratory-confirmed cases are needed to verify the change of vaccine-induced immunity over time.