Seasonal influenza vaccine coverage among high-risk populations in Thailand, 2010–2012

BackgroundThe Advisory Committee on Immunization Practice of Thailand prioritizes seasonal influenza vaccinations for populations who are at highest risk for serious complications (pregnant women, children 6 months–2 years, persons ≥65 years, persons with chronic diseases, obese persons), and healthcare personnel and poultry cullers. The Thailand government purchases seasonal influenza vaccine for these groups. We assessed vaccination coverage among high-risk groups in Thailand from 2010 to 2012.MethodsNational records on persons who received publicly purchased vaccines from 2010 to 2012 were analyzed by high-risk category. Denominator data from multiple sources were compared to calculate coverage. Vaccine coverage was defined as the proportion of individuals in each category who received the vaccine. Vaccine wastage was defined as the proportion of publicly purchased vaccines that were not used.ResultsFrom 2010 to 2012, 8.18 million influenza vaccines were publicly purchased (range, 2.37–3.29 million doses/year), and vaccine purchases increased 39% over these years. Vaccine wastage was 9.5%. Approximately 5.7 million (77%) vaccine doses were administered to persons ≥65 years and persons with chronic diseases, 1.4 million (19%) to healthcare personnel/poultry cullers, 82,570 (1.1%) to children 6 months–2 years, 78,885 (1.1%) to obese persons, 26,481 (0.4%) to mentally disabled persons, and 17,787 (0.2%) to pregnant women. Between 2010 and 2012, coverage increased among persons with chronic diseases (8.6% versus 14%; p < 0.01) and persons ≥65 years (12%, versus 20%; p < 0.01); however, coverage decreased for mentally disabled persons (6.1% versus 4.9%; p < 0.01), children 6 months–2 years (2.3% versus 0.9%; p < 0.01), pregnant women (1.1% versus 0.9%; p < 0.01), and obese persons (0.2% versus 0.1%; p < 0.01).ConclusionsFrom 2010 to 2012, the availability of publicly purchased vaccines increased. While coverage remained low for all target groups, coverage was highest among persons ≥65 years and persons with chronic diseases. Annual coverage assessments are necessary to promote higher coverage among high-risk groups in Thailand.     

Three-season effectiveness of inactivated influenza vaccine in preventing influenza illness and hospitalization in children in Japan, 2013–2016

ObjectivesWe assessed the vaccine effectiveness (VE) of inactivated influenza vaccine (IIV) in children 6 months to 15 years of age in 2015/16 season. In addition, based on the data obtained during the three seasons from 2013 to 2016, we estimated the three-season VE in preventing influenza illness and hospitalization.MethodsOur study was conducted according to a test-negative case-control design (TNCC) and as a case-control study based on influenza rapid diagnostic test results.ResultsDuring 2015/16 season, the quadrivalent IIV was first used in Japan. The adjusted VE in preventing influenza illness was 49% (95% confidence interval [CI]: 42–55%) against any type of influenza, 57% (95% CI: 50–63%) against influenza A and 34% (95% CI: 23–44%) against influenza B. The 3-season adjusted VE was 45% (95% CI: 41–49%) against influenza virus infection overall (N = 12,888), 51% (95% CI: 47–55%) against influenza A (N = 10,410), and 32% (95% CI: 24–38%) against influenza B (N = 9232). An analysis by age groups showed low or no significant VE in infants or adolescents. By contrast, VE was highest in the young group (1–5 years old) and declined with age thereafter. The 3-season adjusted VE in preventing hospitalization as determined in a case-control study was 52% (95% CI: 42–60%) for influenza A and 28% (95% CI: 4–46%) for influenza B, and by TNCC design, it was 54% (95% CI: 41–65%) for influenza A and 34% (95% CI: 6–54%) for influenza B.ConclusionWe demonstrated not only VE in preventing illness, but also VE in preventing hospitalization based on much larger numbers of children than previous studies.     

Effectiveness of inactivated influenza vaccine in children by vaccine dose, 2013–18

ObjectivesWe assessed the vaccine effectiveness (VE) of inactivated influenza vaccine (IIV) by vaccine dose in children aged 6 months to 12 years for whom two doses are recommended in Japan to ascertain the appropriate vaccine doses.MethodsVE was assessed according to a test-negative case-control design based on rapid influenza diagnostic test (RIDT) results. Children aged 6 months to 12 years with a fever ≥38 °C who had received an RIDT in outpatient clinics of 24 hospitals were enrolled for all five seasons since 2013/14. VE by vaccine dose (none vs. once or twice, and once vs. twice) was analyzed.ResultsIn the dose analysis, 20,033 children were enrolled. Both one- and two-dose regimens significantly reduced cases in preventing any influenza, influenza A, and influenza B, but there was no significant difference in adjusted VE between one- and two-dose regimens overall (adjusted OR, 0.560 [95% CI, 0.505–0.621], 0.550 [95% CI, 0.516–0.586]), 0.549 [95% CI, 0.517–0.583], and 1.014 [95% CI, 0.907–1.135], for none vs. once, none vs. twice, none vs. once or twice, and once vs. twice for any influenza, respectively). Both one- and two-dose regimens significantly reduced cases with any influenza and influenza A every season. Also, both regimens significantly reduced cases of any influenza, influenza A, and influenza B among children aged 1–12 years, especially among those aged 1–5 years. In the 2013/14, 2015/16, and 2016/17 seasons, however, only the two-dose regimen was significantly effective in preventing influenza B. Both one- and two-dose regimens significantly reduced cases involving hospitalization due to any influenza and influenza A.ConclusionsBoth one- and two-doses regimens of IIV were effective in preventing influenza for children aged 6 months to 12 years. The two-dose regimen was more effective against influenza B in some seasons.     

Assessment of influenza vaccine effectiveness in a sentinel surveillance network 2010–13, United States

BackgroundInfluenza vaccines are now widely used to reduce the burden of annual epidemics of influenza virus infections. Influenza vaccine effectiveness (VE) is monitored annually to determine VE against each season's circulating influenza strains in different groups such as children, adults and the elderly. Few prospective surveillance programs are available to evaluate influenza VE against medically attended illness for patients of all ages in the United States.MethodsWe conducted surveillance of patients with acute respiratory illnesses in 101 clinics across the US during three consecutive influenza seasons. We analyzed laboratory testing results for influenza virus, self-reported vaccine history, and patient characteristics, defining cases as patients who tested positive for influenza virus and controls as patients who tested negative for influenza virus. Comparison of influenza vaccination coverage among cases versus controls, adjusted for potential confounders, was used to estimate VE as one minus the adjusted odds ratio multiplied by 100%.ResultsWe included 10,650 patients during three influenza seasons from August 2010 through December 2013, and estimated influenza VE in children 6m–5y of age (58%; 95% CI: 49%–66%), children 6–17y (45%; 95% CI: 34%–53%), adults 18–49y (36%; 95% CI: 24%, 46%), and adults ≥50y (34%, 95% CI: 13%, 51%). VE was higher against influenza A(H1N1) compared to A(H3N2) and B.ConclusionsOur estimates of moderate influenza VE confirm the important role of vaccination in protecting against medically attended influenza virus infection.     

Relationship between Guillain–Barré syndrome,influenza-related hospitalizations,and influenza vaccine coverage

Some studies reported an increased risk of Guillain–Barré syndrome (GBS) within six weeks of influenza vaccination. It has also been suggested that this finding could have been confounded by influenza illnesses. We explored the complex relationship between influenza illness, influenza vaccination, and GBS, from an ecologic perspective using nationally representative data. We also studied seasonal patterns for GBS hospitalizations.Monthly hospitalization data (2000–2009) for GBS, and pneumonia and influenza (P&I) in the Nationwide Inpatient Sample were included. Seasonal influenza vaccination coverage for 2004–2005 through the 2008–2009 influenza seasons (August–May) was estimated from the National Health Interview Survey data. GBS seasonality was determined using Poisson regression. GBS and P&I temporal clusters were identified using scan statistics. The association between P&I and GBS hospitalizations in the same month (concurrent) or in the following month (lagged) were determined using negative binomial regression.Vaccine coverage increased over the years (from 19.7% during 2004–2005 to 35.5% during 2008–2009 season) but GBS hospitalization did not follow a similar pattern. Overall, a significant correlation between monthly P&I and GBS hospitalizations was observed (Spearman's correlation coefficient = 0.7016, p < 0.0001). A significant (p = 0.001) cluster of P&I hospitalizations during December 2004–March 2005 overlapped a significant (p = 0.001) cluster of GBS hospitalizations during January 2005–February 2005. After accounting for effects of monthly vaccine coverage and age, P&I hospitalization was significantly associated (p < 0.0001) with GBS hospitalization in the concurrent month but not with GBS hospitalization in the following month. Monthly vaccine coverage was not associated with GBS hospitalization in adjusted models (both concurrent and lagged). GBS hospitalizations demonstrated a seasonal pattern with winter months having higher rates compared to the month of June.P&I hospitalization rates were significantly correlated with hospitalization rates for GBS. Vaccine coverage did not significantly affect the rates of GBS hospitalization at the population level.     

Birth outcomes following immunization of pregnant women with pandemic H1N1 influenza vaccine 2009–2010

BackgroundFollowing the H1N1 influenza pandemic in 2009, pregnant women were recommended to receive both seasonal (TIV) and H1N1 influenza vaccines. This study presents incidence of adverse birth and pregnancy outcomes among a population of pregnant women immunized with TIV and H1N1 vaccines at Kaiser Permanente Northern California during 2009–2010.MethodsWe telephone surveyed pregnant Kaiser Permanente Northern California members to assess non-medically-attended reactions following H1N1, TIV or both vaccines during 2009–2010 (n = 5365) in a separate study. Here we assessed preterm birth (<37 weeks), very preterm birth (<32 weeks), low birth weight (<2500 g, LBW), very low birth weight (<1500 g), small for gestational age, spontaneous abortions, stillbirths and congenital anomalies among this cohort by comparing incidence and 95% confidence intervals between the following immunization groups: TIV only, H1N1 only, H1N1 prior to TIV immunization, TIV prior to H1N1 and both immunizations given at the same time.ResultsResults did not vary significantly between groups. Comparing H1N1 with TIV, incidence were similar for preterm births (6.37 vs 6.28/100 births), very preterm births (5.30 vs 8.29/1000 births), LBW (4.19 vs 2.90/100 births), very LBW (4.54 vs 5.52/1000 births), small for gestational age (9.99 vs 9.24/1000 births), spontaneous abortion (7.10 vs 6.83/1000 pregnancies), stillbirths (7.10 vs 4.57/1000 pregnancies), and congenital anomalies (2.66 vs 2.43/100 births).ConclusionsAlthough constrained by small sample size, complex vaccine groups, and differential vaccine availability during 2009–2010, this study found no difference in adverse birth outcomes between H1N1 vaccine and TIV.     

Which influenza vaccine formulation should be used in Kenya? A comparison of influenza isolates from Kenya to vaccine strains, 2007–2013

IntroductionEvery year the World Health Organization (WHO) recommends which influenza virus strains should be included in a northern hemisphere (NH) and a southern hemisphere (SH) influenza vaccine. To determine the best vaccine formulation for Kenya, we compared influenza viruses collected in Kenya from April 2007 to May 2013 to WHO vaccine strains.MethodsWe collected nasopharyngeal and oropharyngeal (NP/OP) specimens from patients with respiratory illness, tested them for influenza, isolated influenza viruses from a proportion of positive specimens, tested the isolates for antigenic relatedness to vaccine strains, and determined the percentage match between circulating viruses and SH or NH influenza vaccine composition and schedule.ResultsDuring the six years, 7.336 of the 60,072 (12.2%) NP/OP specimens we collected were positive for influenza: 30,167 specimens were collected during the SH seasons and 3717 (12.3%) were positive for influenza; 2903 (78.1%) influenza A, 902 (24.2%) influenza B, and 88 (2.4%) influenza A and B positive specimens. We collected 30,131 specimens during the NH seasons and 3978 (13.2%) were positive for influenza; 3181 (80.0%) influenza A, 851 (21.4%) influenza B, and 54 (1.4%) influenza A and B positive specimens. Overall, 362/460 (78.7%) isolates from the SH seasons and 316/338 (93.5%) isolates from the NH seasons were matched to the SH and the NH vaccine strains, respectively (p < 0.001). Overall, 53.6% and 46.4% SH and NH vaccines, respectively, matched circulating strains in terms of vaccine strains and timing.ConclusionIn six years of surveillance in Kenya, influenza circulated at nearly equal levels during the SH and the NH influenza seasons. Circulating viruses were matched to vaccine strains. The vaccine match decreased when both vaccine strains and timing were taken into consideration. Either vaccine formulation could be suitable for use in Kenya but the optimal timing for influenza vaccination needs to be determined.     

Pandemic and seasonal vaccine coverage and effectiveness during the 2009–2010 pandemic influenza in an Italian adult population

Objectives

To evaluate the response to pandemic vaccination and seasonal and pandemic vaccine effectiveness (VE) in an Italian adult population, during the 2009?C2010 influenza season.

Methods

Data were recorded by interviewing 19,275 subjects (??35?years), randomly recruited from the general population of the Moli-sani project. Events [influenza-like illness (ILI), hospitalization and death], which had occurred between 1 November 2009 and 31 January 2010 were considered. VE was analyzed by multivariable Poisson regression analysis.

Results

Pandemic vaccine coverage was very low (2.4%) in subjects at high-flu risk, aged 35?C65?years (N?=?8,048); there was no significant preventive effect of vaccine against ILI. Seasonal vaccine coverage was 26.6% in the whole population (63% in elderly and 21.9% in middle-aged subjects at high-flu risk). There was a higher risk to develop ILI in middle-age [VE: ?17% (95% CI: ?35,?1)] or at high flu-risk [VE: ?17% (95% CI: ?39, 2)] vaccinated groups.

Conclusions

Coverage of pandemic vaccine was very low in a Southern Italy population, with no protective effect against ILI.     

The 2015–2016 influenza epidemic in Beijing,China: Unlike elsewhere,circulation of influenza A(H3N2) with moderate vaccine effectiveness

BackgroundWhile the 2015–2016 influenza season in the northern hemisphere was dominated by A(H1N1)pdm09 and B/Victoria viruses, in Beijing, China, there was also significant circulation of influenza A(H3N2) virus. In this report we estimate vaccine effectiveness (VE) against influenza A(H3N2) and other circulating viruses, and describe further characteristics of the 2015–2016 influenza season in Beijing.MethodsWe estimated VE of the 2015–2016 trivalent inactivated vaccine (TIV) against laboratory-confirmed influenza virus infection using the test-negative study design. The effect of prior vaccination on current VE was also examined.ResultsOf 11,000 eligible patients included in the study, 2969 (27.0%) were influenza positive. Vaccination coverage was 4.2% in both cases and controls. Adjusted VE against all influenza was 8% (95% CI: −16% to 27%): 18% (95% CI: −38% to 52%) for influenza A(H1N1)pdm09, 54% (95% CI: 16% to 74%) for influenza A(H3N2), and −8% (95% CI: −40% to 18%) for influenza B/Victoria. The overall VE for receipt of 2015–2016 vaccination only, 2014–2015 vaccination only, and vaccinations in both seasons was −15% (95% CI: −63% to 19%), −25% (95% CI: −78% to 13%), and 18% (95% CI: −11% to 40%), respectively.ConclusionsOverall the 2015–2016 TIV was protective against influenza infection in Beijing, with higher VE against the A(H3N2) viruses compared to A(H1N1)pdm09 and B viruses.     

Seasonal influenza vaccine effectiveness against influenza in 2012–2013: A hospital-based case-control study in Lithuania

Background

Due to scarce information on seasonal influenza vaccine effectiveness (SIVE) against severe clinical influenza outcomes in risk populations, we conducted a case-control study to assess its effects against laboratory-confirmed influenza in hospitalized patients during the 2012–2013 influenza season.

Methods

We conducted a test-negative case-control study among ≥18 years old patients with influenza-like illness (ILI) hospitalized in two Lithuanian hospitals. Cases were influenza A(H1N1), A(H3) or influenza B positive by RT-PCR, and controls were influenza negative. Additional demographic and clinical data to assess the role of confounding were collected. SIVE and its confidence intervals (95% CI) were estimated by using multivariate logistic regression as (1 − OR) × 100%.

Results

The sample consisted of 185 subjects. Seasonal influenza vaccine uptake was 5%. Among 111 (60%) influenza positive cases, 24.3% were A(H1N1), 10.8% were A(H3) and 24.3% were influenza B cases. Unadjusted SIVE was 79% (95% CI −6% to 96%) and after the adjustment it increased to 86% (95% CI 19% to 97%).

Conclusions

Seasonal influenza vaccination in 2012–2013 was associated with reduced occurrence of laboratory-confirmed influenza, but due to low sample size the estimate of SIVE is imprecise. Given high prevalence of influenza in hospitalized ILI cases and low influenza vaccination coverage, there is a need to increase influenza vaccination rates.     

Midwives’ attitudes toward participation of pregnant individuals in a preventive vaccine hypothetical clinical trial

IntroductionPregnant individuals are frequently excluded from clinical trials. Yet, inclusion of Pregnant individuals is of interest in vaccinology including during health crisis. Promotion of clinical trials by midwives may facilitate the decision making of Pregnant individuals. Attitudes of midwives about pregnant individuals participation in a vaccine clinical trial have been little explored.MethodsWe conducted an anonymous survey from the 11th of September to the 11th of November 2020. Primary endpoint was the willingness to encourage Pregnant individuals to participate in a hypothetical respiratory syncytial virus (RSV) vaccine clinical trial.ResultsAmong 398 midwives who answered the questionnaire, 113 (28.3 %) were likely to encourage Pregnant individuals to participate in the vaccine clinical trial, this proportion ranged from 25 % in senior midwives to 34.5 % among the students. After adjustment on age, parenthood, previous personal attitudes of vaccine hesitancy, and psychological antecedents of vaccinations (5C-model), the only predictor of the promotion of the clinical trial was the experience of vaccine education (evaluated by a 20-point score) with an adjusted odds ratio of 1.09 (1.01–1.18, p = 0.027) for a one-point increase. Vaccine hesitancy and psychological antecedents of vaccinations were not associated with a lower promotion of pregnant individuals trial participation by midwives.ConclusionFew respondents were likely to encourage Pregnant individuals to participate in a vaccine clinical trial. Midwives who considered themselves to have a good training about vaccines were more prone to encourage Pregnant individuals to participate in a RSV vaccine clinical trial.     

A real-world study evaluating the relative vaccine effectiveness of a cell-based quadrivalent influenza vaccine compared to egg-based quadrivalent influenza vaccine in the US during the 2017–18 influenza season

BackgroundCell-based influenza vaccine manufacturing reduces egg adaptations that can decrease vaccine effectiveness. We evaluated the relative vaccine effectiveness (rVE) of cell-based quadrivalent influenza vaccine (QIVc) compared to standard-dose egg-based quadrivalent influenza vaccines (QIVe-SD) against influenza-related and serious respiratory events among subjects 4–64 years of age during the 2017–18 influenza season.MethodsA retrospective cohort analysis was conducted using administrative claims data in the US (IQVIA PharMetrics Plus® database). Subjects vaccinated with QIVc or QIVe-SD from 8/2017–1/2018 were identified (date of vaccination termed the index date). Influenza-related hospitalizations/ER visits, all-cause hospitalizations and serious respiratory hospitalizations/ER visits were assessed post-vaccination. Inverse probability of treatment weighting (IPTW) and Poisson regression were used to evaluate the adjusted rVE of QIVc compared to QIVe-SD. In a subgroup analysis, rVE was assessed for several subgroups of interest (4–17, 18–64 and 50–64 years, and subjects with ≥1 high-risk condition). In a secondary economic analysis, annualized all-cause costs over the follow-up were compared using propensity score matching (PSM) and generalized estimating equation (GEE) models.ResultsThe study sample comprised 555,538 QIVc recipients and 2,528,524 QIVe-SD recipients. Prior to adjustment, QIVc subjects were older and had higher total costs in the 6-months pre-index. Following IPTW-adjustment and Poisson regression, QIVc was more effective in reducing influenza-related hospitalizations/ER visits, all-cause hospitalizations, and hospitalizations/ER visits related to asthma/COPD/bronchial events and other respiratory events compared to QIVe-SD. Similar trends were generally observed in the subgroup analysis. Following PSM adjustment and GEE regression, QIVe-SD was associated with significantly higher annualized all-cause total costs compared to QIVc, driven by higher costs for outpatient medical services and inpatient hospitalizations.ConclusionsAfter adjustment for confounders and selection bias, QIVc reduced influenza-related hospitalizations/ER visits, all-cause hospitalizations, and serious respiratory hospitalizations/ER visits compared to QIVe-SD. QIVc was associated with significantly lower all-cause total costs.     

High-dose influenza vaccine use among patients receiving hemodialysis in the United States, 2010–2013

BackgroundStandard influenza vaccines may be of limited benefit to patients with end-stage renal disease (ESRD). These patients may benefit from high-dose influenza vaccine, currently indicated for patients aged ≥65 years. Studies in other populations have demonstrated that high-dose vaccine elicits a stronger immunological response. We compared vaccine uptake in the United States and predictors of receipt for high-dose and standard influenza vaccines.MethodsUsing data from the United States Renal Data System (2010–2013), we conducted a cohort study of 421,482 adult patients on hemodialysis. We examined temporal trends in uptake of high-dose or standard trivalent influenza vaccine each influenza season, and used multivariate logistic regression to assess the association between individual-level variables (e.g., demographics, comorbidities) and facility-level variables (e.g., facility size and type) with vaccine receipt.ResultsThe proportion of patients with ESRD who were vaccinated with any influenza vaccine increased from 68.3% in 2010 to 72.4% in 2013. High-dose vaccines were administered to 0.9% of patients during the study period, and 16.7% of high-dose vaccines were administered to patients <65 years of age. Among patients aged ≥65 years, older patients (>79 vs. 65–69 years: OR, 1.29; 95% CI, 1.19–1.41) and patients at hospital-based versus free-standing dialysis facilities (OR, 2.31; 95% CI, 2.13–2.45) were more likely to receive high-dose vaccine, while blacks (vs. whites [OR, 0.66; 95% CI, 0.61–0.71]) and patients with longer duration of ESRD (>9 vs. 0 years: OR, 0.66; 95% CI, 0.55–0.78) were less likely to receive the high-dose vaccine.ConclusionsWhile the overall influenza vaccination rate has increased, use of high-dose vaccine among patients with ESRD was very low. Being an older patient, living in the Midwest, and receiving care at hospital-based facilities were the strongest predictors of receiving high-dose vaccine.     

Usage of quadrivalent influenza vaccine among children in the United States, 2013–14

Annual influenza vaccination is recommended for everyone ≥6 months in the U.S. During the 2013–14 influenza season, in addition to trivalent influenza vaccines, quadrivalent vaccines were available, protecting against two influenza A and two influenza B viruses. We analyzed 1,976,443 immunization records from six sentinel sites to compare influenza vaccine usage among children age 6 months–18 years. A total of 983,401 (49.8%) influenza vaccine doses administered were trivalent and 920,333 (46.6%) were quadrivalent (unknown type: 72,709). Quadrivalent vaccine administration varied by age and was least frequent among those <2 years of age.     

Workplace availability,risk group and perceived barriers predictive of 2016–17 influenza vaccine uptake in the United States: A cross-sectional study

BackgroundSeasonal influenza, though mostly self-limited in the healthy adult, may lead to severe disease and/or complications in subpopulations. Annual influenza vaccination is available in many countries with coverage goals rarely being met. We conducted a cross-sectional study of influenza vaccine uptake and explored socio-demographic, economic, and psychological factors that explained vaccine uptake.MethodsThe survey was administered via Amazon Mechanical Turk (MTurk) to United States residents in January 2017, using the Qualtrics platform. Using principal axis factor analysis, we reduced the 25 items theory-based psychological determinants into the primary constructs they measure if/when internal consistency was sufficient (Cronbach’s alpha >0.60). Logistic regression models were used to quantify the association of socio-demographic, economic, and psychological factors with reported vaccine behavior in the 2016–17 flu season.Results1007 participants completed the survey, sex distribution was even, 67% had 25–44 years of age, and 61% annual household income of $30–99 thousand United States dollars. About 25% had the flu shot offered at their workplace and 20% reported belonging to a group for whom the flu shot is recommended. Vaccine uptake was 31.5%. Eight predictors remained in the final adjusted model (R² = 0.489), having the vaccine offered at the workplace, belonging to a group for whom the vaccine is recommended, and higher perceived barriers were the strongest predictors of vaccine uptake, increasing (and decreasing in the case of barriers) the odds by >3-fold. Additionally, higher household income, higher perceived susceptibility and higher perceived benefits also independently predicted vaccine uptake.DiscussionWe found evidence that perceived barriers significantly impaired vaccine uptake to the same extent that having the vaccine offered at the workplace or belonging to a group for whom the vaccine is recommended facilitated uptake. Ideally, a better understanding of drivers of vaccine hesitancy will result in improved interventions to increase vaccine uptake.     

Estimation of oral poliovirus vaccine effectiveness in Afghanistan, 2010–2020

BackgroundAfghanistan is one of two countries with endemic wild poliovirus type 1 (WPV1). The oral poliovirus vaccine (OPV) is the predominant vaccine used for polio eradication. Although OPV has been administered in routine childhood immunization and during frequent supplementary immunization activities, WPV1 continues to circulate in Afghanistan and case incidence has been increasing since 2017. We estimated the effectiveness of OPV in Afghanistan during 2010–2020.MethodsWe conducted a matched case-control analysis using acute flaccid paralysis (AFP) surveillance data from 29,370 children < 15 years with AFP onset between January 1, 2010 and December 31, 2020. We matched children with confirmed WPV1 (cases) with children with non-polio AFP (controls) by age at onset of paralysis (+/- 3 months), date of onset of paralysis (+/- 3 months), and province of residence, and compared their reported OPV vaccination history to estimate the effectiveness of OPV in preventing paralysis by WPV1 using conditional logistic regression. To account for changes in OPV formulations provided over the analysis period, we stratified the analysis based on dates of the global switch from trivalent OPV (tOPV) to bivalent OPV (bOPV) in April 2016.ResultsBetween January 1, 2010 and December 31, 2020, there were 329 WPV1 cases in Afghanistan. The per-dose estimated effectiveness of OPV against WPV1 was 19% (95% CI: 15%–22%) and of ≥ 7 doses was 94% (95% CI: 90%-97%). Before the global switch from tOPV to bOPV, the per-dose estimated effectiveness of OPV was 14% (95% CI: 11%-18%) and of ≥ 7 doses was 92% (95% CI: 85%-96%). After the switch, the per-dose estimated effectiveness of OPV against WPV1 was 32% (24%-39%) and of ≥ 7 doses was 96% (95% CI: 90%-99%).DiscussionOPV is highly effective in preventing paralysis by WPV1; these results indicate that continued WPV1 transmission in Afghanistan is due to failure to vaccinate, not failure of the vaccine. Although difficult to implement in parts of country, improving the administration of OPV in routine immunization and supplementary immunization activities will be critical for achieving polio eradication in Afghanistan.     

Interim influenza vaccine effectiveness: A good proxy for final estimates in Spain in the seasons 2010–2014

IntroductionThe agreement between interim and final influenza vaccine effectiveness (VE) estimates would support the use of interim assessments as a proxy for final VE results to guide health authorities in influenza prevention. We aimed to compare interim/final VE estimates in Spain.MethodsWe used a test-negative case-control study (cycEVA) for 2010/11–2013/14 seasons. Sensitivity analyses were carried out by type/subtype of influenza virus and by target groups for vaccination.ResultsIn general, interim estimates were higher compared to end-season estimates. Interim and final VE differences were higher for the target groups compared to all population. Subtype-specific interim/final VE estimates showed greater concordance (3–13%) than for any virus (7–24%).ConclusionIn Spain, interim influenza VE estimates over 2010–2014 were a good proxy of the final protection of the vaccine. Interim and final estimates showed greater concordance for all population and if performed subtype-specific.