Differential determinants and reasons for the non- and partial vaccination of children among Nigerian caregivers

BackgroundVaccination has saved millions of lives. However, the vaccination rate in Nigeria remains low. We differentiate reasons for incomplete vaccination by status: not- and partially- vaccinated, and examine the association between sociodemographic characteristics of caregivers and reasons for incomplete vaccination.MethodsData from the Multiple Indicator Cluster Survey (MICS) conducted in Nigeria in 2016 and 2017 was analyzed. The logistic regression was used to evaluate associations between sociodemographic characteristics of caregivers and incomplete vaccination according to different reasons.ResultsThe most common reason for non-vaccination is that caregivers have no faith in immunization (27.0%), followed by lack of awareness of the need for immunization (26.0%) and the perception that the place where immunization is given is too far/inconvenient (24.3%). The most common reason for partial vaccination is that caregivers thought the children had already been fully immunized (44.8%), followed by the inconvenient location for immunization (15.3%) and supply-side issues such as shortage of vaccine stock and absence of vaccinators (14.4%). Among caregivers whose children are never vaccinated, a lower level of education is correlated with more likelihood of having no faith in immunization and poorer households are more likely to state a lack of awareness of the need for immunization need and an inconvenient place as the reasons for non-vaccination. Among caregivers whose children are only partially vaccinated, educated and wealthier caregivers are more likely to state that they thought their children were fully vaccinated, while poorer caregivers tend to give an inconvenient immunization place as the reason for incomplete vaccination. Supply-side barriers are not systematically correlated with educational attainment or wealth level of caregivers.ConclusionBarriers to vaccination are different according to vaccination status: not- and partially- vaccinated, as is the association between sociodemographic characteristics of caregivers and reasons for incomplete vaccination. The policy to increase vaccination take-up should take these differentials into consideration.     

Seasonal influenza vaccination rates and reasons for non-vaccination in children with gastrointestinal disorders

ObjectivesDespite advances in the treatment and prevention of influenza, it is still considered an important cause of morbidity and mortality worldwide. Annual vaccination is the safest and most effective mean of prevention. Our study aims were to explore the uptake of influenza vaccination among children with gastrointestinal disorders, and to characterize non-adherent patients.MethodsThe present cross-sectional study included parents of pediatric patients attending the Gastroenterology Institute at Schneider Children's Medical Center of Israel between September and October 2011. Parents were asked to complete a questionnaire concerning demographic and clinical parameters, influenza vaccination of the child, and reasons for not vaccinating the child, when appropriate.ResultsThe study population included 273 patients (50% female), with a median age of 10 years (range, 2–18 years). Overall, the rate of seasonal influenza vaccination was 30.8%. Higher rates were found among immunosuppressed patients (46.1%), and in patients with inflammatory bowel disease (50%). There was no significant effect of patient age, gender, ethnic origin or parental level of education on the vaccination rate. Vaccination rates were significantly associated with parents’ information and knowledge of, as well as their personal beliefs regarding the vaccine (P < 0.001).ConclusionsInfluenza vaccination rates are relatively low in the pediatric population attending gastroenterology clinics, in both high- and low-risk groups. The importance of parental knowledge in compliance with influenza vaccination of children should prompt general pediatricians and gastroenterologists to discuss and address the common misconceptions regarding the vaccine.     

Variations in reason for intention not to vaccinate across time,region, and by race/ethnicity,NIS-Teen (2008–2016)

Background

Human papillomavirus (HPV) vaccination is expected to reduce HPV-related disease and cancer in the US. However, many parents are hesitant to obtain the vaccine for their children. The purpose of this study is to examine how the reasons for refusing the HPV vaccine vary across regions of the US, across time, and by race/ethnicity.

Exploring the heterogeneity among partially vaccinated children in a population-based cohort

IntroductionVaccination status is often categorized as complete or not-complete. This ignores the potentially important heterogeneity in children whose vaccinations are not-complete. We sought to subcategorize not-completely vaccinated children and determine whether characteristics differed among these subgroups.MethodsThis retrospective cohort study assessed vaccination status at 2 years of age for 43,965 children in the 2008 Alberta (Canada) birth cohort who were registered with provincial vital statistics records. Children were categorized (based on the five routinely scheduled childhood vaccines) as complete, incomplete, selective, or non-vaccination status. Characteristics derived from administrative health databases were used to determine factors associated with vaccination status.ResultsPopulation-level vaccination status at 2 years of age was found to be: 71.1% complete and 28.9% not complete (21.9% incomplete, 2.0% selective, and 5.1% non-vaccinated). Midwife delivery at home, compared to physician delivery in hospital, was strongly associated with non-vaccination status (adjusted odds ratio [aOR] 51.70, 95% CI 37.10–72.10). Factors that might pose barriers to vaccination, such as single marital status (aOR 1.58, 95% CI 1.49–1.67), large number of household children (≥4 vs. 1) (aOR 3.24, 95% CI 2.95–3.54), and multiple household moves (≥3 vs. 0) (aOR 1.69, 95% CI 1.35–2.10), were all strongly associated with incomplete vaccination status.ConclusionsOf the children who were not completely vaccinated at age 2, the vast majority had started but not completed the vaccination series, while a smaller number were selectively vaccinated or not vaccinated at all. Distinct differences are present among these groups that require attention when addressing vaccine coverage.     

Intention to accept pertussis vaccine among pregnant women in Karachi,Pakistan

BackgroundMaternal immunization against pertussis is a potential strategy to protect young infants from severe disease. We assessed factors associated with intention to accept pertussis vaccination among pregnant women in Karachi, Pakistan.MethodsWe conducted a cross-sectional survey between May and August 2013 in pregnant women who visited healthcare centers in urban slums of Karachi city. Women completed a survey examining socio-demographic factors, vaccination history, knowledge on pertussis disease, perception of vaccine recommendation sources, and potential influences on vaccine decision-making.ResultsOf the 283 participants, 259 (92%) provided their intention to either accept or decline pertussis vaccination. Eighty-three percent women were willing to accept the pertussis vaccine if offered during pregnancy. About half (53%) of the participants had ever heard of pertussis disease. Perceptions of pertussis vaccine efficacy, safety, and disease susceptibility were strongly associated with intention to accept pertussis vaccine (p < 0.01). Healthcare providers, Ministry of Health, and mass media were considered as highly reliable sources of vaccine recommendation and associated with intention to accept antenatal pertussis vaccination (p < 0.001). Healthcare provider recommendation was a common reason cited by respondents for pregnant women to accept antenatal pertussis vaccination (p = 0.0005). However, opinion of primary decision-makers in the family (husbands and in-laws) was a crucial reason cited by respondents for pregnant women to reject pertussis vaccination in pregnancy (p = 0.003).ConclusionAntenatal pertussis vaccination initiatives in South Asia should strongly consider inclusion of family members, healthcare providers, national health ministries, and mass media to help implement new vaccination programs.     

Differential coverage for vaccines in the expanded program on immunization (EPI) among children in rural Pakistan

BackgroundPakistan has a well-established Expanded Program on Immunization (EPI) however vaccine-preventable diseases still account for high infant and child mortality rates. This study describes the differential vaccine coverage and determinants of vaccine uptake in rural Pakistan.MethodsFrom October 2014 to September 2018, we enrolled children younger than 2 years of age from the Matiari Demographic Surveillance System in Sindh, Pakistan. Socio-demographic and vaccination history were collected from all participants. Vaccine coverage rates and timeliness were reported. Socio-demographic variables for missed and untimely vaccination were studied in multivariable logistic regression.ResultsOf the 3140 enrolled children, 48.4 % received all EPI recommended vaccines. Only 21.2 % of these were age appropriate. Around 45.4 % of the children were partially vaccinated, and 6.2 % were unvaccinated. Highest coverage was seen for the first dose of pentavalent (72.8 %), 10-valent Pneumococcal Conjugate Vaccine (PCV10) (70.4 %) and Oral Polio Vaccine (OPV) (69.2 %) and the lowest coverage was for measles (29.3 %) and rotavirus (1.8 %) vaccines. Primary caretakers and wage earners with a higher level of education were protective against missed and untimely vaccination. Enrollment in the 2nd, 3rd and 4th study year was negatively associated with being unvaccinated whereas distance from a major road was positively associated with non-adherence to schedule.ConclusionVaccine coverage was low among children in Matiari, Pakistan, and majority received delayed doses. Parents’ education status and year of study enrollment was protective against vaccine dropout and delayed vaccination whereas geographical distance from a major road was a predictor. Vaccine promotion and outreach efforts may have had a beneficial impact on vaccine coverage and timeliness.     

Acceptability of the human papillomavirus vaccine and reasons for non-vaccination among parents of adolescent sons

Routine administration of the quadrivalent human papillomavirus (HPV) vaccine has been recommended for 11–12-year-old males since 2011, but coverage remains low. In a U.S. national sample of parents of 11–17-year-old males (n = 779), 78.6% of parents reported their sons had not received the HPV vaccine. The most common reason for non-vaccination (56.7%) was “My doctor or healthcare provider has not recommended it.” Parents citing only logistical reasons for non-vaccination (e.g., lack of recommendation, access, or education, n = 384) reported significantly higher vaccine acceptability than parents reporting a combination of attitudinal (e.g., concerns about vaccine safety or efficacy) and logistical barriers (n = 92), while parents citing only attitudinal barriers (n = 73) reported the lowest level of vaccine acceptability. In sum, many parents are willing but have not vaccinated sons due to logistical barriers, most commonly lack of healthcare provider recommendation. These findings have important implications for increasing HPV vaccination coverage among adolescent males.     

Refusal of oral polio vaccine in northwestern Pakistan: A qualitative and quantitative study

Background

Refusal of the oral polio vaccine (OPV) is a difficulty faced by the Polio Eradication Initiative (PEI) in multiple endemic areas, including the Khyber Pakhtunkhwa Province (KPP), Pakistan. In 2007, we investigated community perceptions of the OPV and estimated the prevalence of OPV refusal in three districts in Swat Valley, KPP, a polio-endemic area.

Methods

Qualitative data concerning community perceptions were collected by focus group discussions among lady health workers (LHWs) and mothers with children <1 year old and by key informant interviews with local health managers and officials. Quantitative data collection followed using a questionnaire survey of 200 LHWs and a cluster sampling survey of 210 mothers (per district) with children <1 year old.

Results

The qualitative assessments identified the grounded theory of OPV refusal involving facts known by the residents that are related to the OPV (too frequent OPV campaigns, an OPV boycott in northern Nigeria in 2003 and that birth control is viewed as is against Islam), the local interpretations of these facts (perceptions that OPV contained birth control or pork, that OPV was a foreign/central plot against Muslims, and that the vaccination was against the Hadith and the fate determined by God) and different manifestations of OPV refusal. Among the three districts studied, the proportion of LHWs who encountered OPV refusal ranged from 0 to 33%, whereas among the districts, the proportions of mothers unwilling to give OPV to their children ranged from 0.5 to 5.7%. Refusal of other injectable vaccines was almost equally prevalent for reasons that were very similar.

Conclusions

The PEI needs to reflect local value system in the path to polio eradication in the studied districts in the Swat Valley. The religious and cultural values as well as the interpretation of the international political situation are of particular importance.     

Parental attitudes towards mandatory vaccination; a systematic review

Uptake of childhood vaccines is decreasing. While mandatory vaccination schemes can increase vaccine uptake rates, they can also cause backlash among some parents. We conducted a systematic review investigating parental beliefs about vaccine mandates and factors associated with support for mandatory vaccination schemes. We searched Embase, Ovid MEDLINE, Global Health, APA PsycINFO and Web of Science from inception to 17th September 2020. Seventeen studies (five qualitative, twelve quantitative) were eligible for inclusion. We synthesised results of qualitative and quantitative studies separately. As quantitative studies were heterogeneous in the mandatory vaccination schemes and associated factors investigated, there was no scope to conduct a meta-analysis. Instead, data were narratively synthesised, considering risk of bias ratings. Qualitative data were synthesised using meta-ethnography, synthesising themes reported across studies included. Quantitative studies reported that support for mandatory vaccination schemes was reasonably high (73% to 88%). However, due to heterogeneity, there was little evidence for any factors being consistently associated with support for mandatory vaccination. Qualitative studies gave an insight into how parents perceive mandatory vaccination. Studies found that parents perceived mandatory vaccination schemes as an infringement of their rights, and particularly disliked schemes offering financial incentives for vaccination. Nevertheless, some parents felt that schemes limiting access to schooling of unvaccinated children gave them “peace of mind.” Results should be taken with caution due to the purposive use of non-representative samples. Before deciding to mandate vaccination, it is important to understand the impact it could have on parental beliefs and attitudes about vaccination.     

Awareness among adults of vaccine-preventable diseases and recommended vaccinations,United States, 2015

BackgroundAdults are recommended to receive select vaccinations based on their age, underlying medical conditions, lifestyle, and other considerations. Factors associated with awareness of vaccine-preventable diseases and recommended vaccines among adults in the United States have not been explored.MethodsData from a 2015 internet panel survey of a nationally representative sample of U.S. adults aged ≥19 years were analyzed to assess awareness of selected vaccine-preventable diseases and recommended vaccines for adults. A multivariable logistic regression model with a predictive marginal approach was used to identify factors independently associated with awareness of selected vaccine-preventable infections/diseases and corresponding vaccines.ResultsAmong the surveyed population, from 24.6 to 72.1% reported vaccination for recommended vaccines. Awareness of vaccine-preventable diseases among adults aged ≥19 years ranged from 63.4% to 94.0% (63.4% reported awareness of HPV, 71.5% reported awareness of tetanus, 72.0% reported awareness of pertussis, 75.4% reported awareness of HZ, 75.8% reported awareness of hepatitis B, 83.1% reported awareness of pneumonia, and 94.0% reported awareness of influenza). Awareness of the corresponding vaccines among adults aged ≥19 years ranged from 59.3% to 94.1% (59.3% HZ vaccine, 59.6% HPV vaccine, 64.3% hepatitis B vaccine, 66.2% pneumococcal vaccine, 86.3% tetanus vaccines, and 94.1% influenza vaccine). In multivariable analysis, being female and being a college graduate were significantly associated with a higher level of awareness for majority of vaccine-preventable diseases, and being female, being a college graduate, and working as a health care provider were significantly associated with a higher level of awareness for majority of corresponding vaccines.ConclusionsAlthough adults in this survey reported high levels of awareness for most vaccines recommended for adults, self-reported vaccination coverage was not optimal. Combining interventions known to increase uptake of recommended vaccines, such as patient reminder/recall systems and other healthcare system-based interventions, and ensuring patients’ vaccination needs are assessed, are needed to improve vaccination of adults.     

Reasons for non-vaccination against HPV and future vaccination intentions among 19-26 year-old women

Background  

Despite CDC recommendations regarding universal catch-up vaccination against human papillomavirus (HPV), only about ten percent of young adult women in the United States have been vaccinated. The purpose of this study was to better understand reasons for non-vaccination among insured 19-26 year-old women and to evaluate future vaccination intentions.     

Knowledge and recommendation regarding routine childhood vaccinations among pediatric healthcare providers in Israel

BackgroundA recommendation by pediatric healthcare providers (HCPs) is a major factor influencing parents' decision to vaccinate their children. Consequently, it is important to understand the motives behind the HCPs' recommendations to vaccinate children according to the routine immunization program.ObjectivesTo study the association of pediatric HCPs' knowledge about and attitudes towards childhood vaccinations and of their professional and demographic characteristics, with two variables: 1. Their recommendations to parents regarding adherence to the routine immunization program. 2. Their choices concerning routine immunization of their own children.Study design and settingsWe conducted a cross-sectional study of pediatric nurses and physicians working at Mother-Child Health Clinics (MCHCs) in Haifa and Tel-Aviv districts and at a hospital in Hadera City, Israel.MethodsA structured, anonymous self-administered questionnaire was used.ResultsThe overall response rate was 60%, totaling 218 participants. 92% of whom were nurses. Misconceptions related to vaccine safety were found among a high percentage of the participants. The HCPs knowledge level was associated with the HCPs vaccinating their own children according to the recommended immunization program (OR = 1.32; CI95% 1.06–1.64), but not with their recommendation to parents to adhere to the program. No association was found between attitudes and these variables. Workplace (MCHCs versus hospital) correlated with the above mentioned two dependent variables (OR = 1.89; CI95% 1.21–2.97 and OR = 2.42; CI95% 1.73–3.4, respectively).ConclusionsAmplifying the knowledge of HCPs and addressing their concern about vaccinations can improve their adherence to the routine immunization program regarding their own children. This may lead to better adherence of other parents who are frequently interested in the HCPs' behavior and consider them as a role model. In general, there is a need to emphasize the HCP's responsibility for the successful implementation of the immunization program in the community and at hospitals.     

Reasons related to non-vaccination and under-vaccination of children in low and middle income countries: findings from a systematic review of the published literature, 1999-2009

Objective

Despite increases in routine vaccination coverage during the past three decades, the percent of children completing the recommended vaccination schedule remains below expected targets in many low and middle income countries. In 2008, the World Health Organization Strategic Advisory Group of Experts on Immunization requested more information on the reasons that children were under-vaccinated (receiving at least one but not all recommended vaccinations) or not vaccinated in order to develop effective strategies and interventions to reach these children.

Methods

A systematic review of the peer-reviewed literature published from 1999 to 2009 was conducted to aggregate information on reasons and factors related to the under-vaccination and non-vaccination of children. A standardized form was used to abstract information from relevant articles identified from eight different medical, behavioural and social science literature databases.

Findings

Among 202 relevant articles, we abstracted 838 reasons associated with under-vaccination; 379 (45%) were related to immunization systems, 220 (26%) to family characteristics, 181 (22%) to parental attitudes and knowledge, and 58 (7%) to limitations in immunization-related communication and information. Of the 19 reasons abstracted from 11 identified articles describing the non-vaccinated child, 6 (32%) were related to immunization systems, 8 (42%) to parental attitudes and knowledge, 4 (21%) to family characteristics, and 1 (5%) to communication and information.

Conclusions

Multiple reasons for under-vaccination and non-vaccination were identified, indicating that a multi-faceted approach is needed to reach under-vaccinated and unvaccinated children. Immunization system issues can be addressed through improving outreach services, vaccine supply, and health worker training; however, under-vaccination and non-vaccination linked to parental attitudes and knowledge are more difficult to address and likely require local interventions.     

Comparison of antibody response between boys and girls after infant and childhood vaccinations in the Netherlands

BackgroundInfectious diseases can differ by sex in their incidence, prevalence, or severity of disease. These differences may be induced by sex-dependent immune responses and resulting protection, for example after vaccination. Therefore, this study aims to assess possible sex-differences in immunoglobulin levels (IgG) after infant and childhood vaccination.MethodsData from a national cross-sectional serosurvey conducted in 2006/2007 were used (Pienter 2). We compared IgG levels against measles, mumps, rubella, diphtheria, tetanus, poliomyelitis, pertussis, Haemophilus influenzae type b (Hib), and Neisseria meningitidis serogroup C (MenC) between girls and boys both short term (1 month to 1 year) and long term (1–3 year) after infant and childhood vaccinations, using linear regression analysis. Proportions of boys and girls reaching a protective IgG level were compared using Fishers exact test.ResultsDifferences in IgG were found at specific time points after vaccination against measles, mumps, rubella, MenC, and polio. The geometric mean concentration or titer (GMC/T) girls:boys ratios ranged between 1.10 for polio type 1 <1 year after the first childhood booster to 1.90 for MenC <1 year after infant vaccination, indicating higher antibody levels in girls. No significant differences were found between boys and girls for diphtheria, tetanus, pertussis, and Hib at either time point. Proportions with protective levels differed only at 1–3 years after infant vaccination for mumps (82.5% boys vs. 91.9% girls, p = 0.046), and at the same time point for MenC (7.0% boys vs. 18.2% girls, p = 0.015), and polio type 1 (87.8% boys vs. 95.9% girls, p = 0.047).ConclusionDifferences in IgG between boys and girls were generally small and not consistent, neither between pathogens nor within pathogens. If differences were observed, girls were favored over boys. On the whole, the results suggest that there are no major sex differences in protection from the studied pathogens in the Netherlands.     

Intent to obtain pediatric influenza vaccine among mothers in four middle income countries

BackgroundDespite a large burden of influenza in middle income countries, pediatric vaccination coverage remains low. The aims of this study were to (1) describe mothers’ knowledge and attitudes about influenza illnesses and vaccination, and (2) identify characteristics associated with mothers’ intent to vaccinate their child.MethodsFrom 2015 to 2017, infants 0–11 months old in Nicaragua, Philippines, Jordan, and Albania were enrolled from community settings and hospitals. Interviewers administered a questionnaire to their mothers. Mothers of infants aged 6–11 months rated their intention (small-to-moderate vs. large chance) to accept pediatric vaccination if it was offered at no-cost. The importance of knowledge, attitudes, and sociodemographic characteristics in predicting influenza vaccination intention was measured as the mean decrease in Gini index when that factor was excluded from 1000 decision trees in a random forest analysis.ResultsIn total, 1,308 mothers were enrolled from the community setting and 3,286 from the hospital setting. Prevalence of at least some knowledge of influenza illness ranged from 34% in Philippines to 88% in Albania (in the community sample), and between 23% in Philippines to 88% in Jordan (in the hospital sample). In the community sample, most mothers in Albania (69%) and Philippines (58%) would accept the influenza vaccine, and these proportions were higher in the hospital sample for all countries except Albania (48%) (P < 0.0001). Perceived vaccine safety (mean decrease in Gini index = 61) and effectiveness (55), and perceived knowledge of influenza vaccine (45) were the most important predictors of influenza vaccination intention in models that also included country and community versus hospital sample.ConclusionIntent to vaccinate infants aged 6–11 months in four middle income countries was tied primarily to knowledge of the vaccine and perceptions of vaccine safety and effectiveness. These findings were noted among mothers interviewed in the community and mothers of recently hospitalized infants.     

Influenza and pneumococcal vaccinations are not associated to COVID-19 outcomes among patients admitted to a university hospital

In order to reduce the burden on healthcare systems and to support differential diagnosis with COVID-19, influenza and pneumococcal vaccinations were strongly recommended during the COVID-19 pandemic, especially in vulnerable groups. However, no univocal and conclusive evidence on the relationship between influenza and pneumococcal vaccinations and COVID‐19 outcomes exists. We evaluated the association between such vaccinations, COVID-19 hospitalization, intensive care unit admissions and deaths in a cohort (N = 741) of COVID-19 patients who had access to the emergency room of a large Italian University hospital between March 1, 2020 and June 1, 2020. Results show that influenza and pneumococcal vaccinations did not affect hospitalization, intensive care unit admission and deaths in COVID-19 patients in the overall sample and in those ≥65 years. The same pattern of results was confirmed considering timing of influenza vaccine administration, vaccination type, and number of uptakes in the last five vaccination campaigns. In conclusion, our study does not support an impact of influenza and pneumococcal vaccinations on COVID-19 outcomes.     

Education level modifies parental hesitancy about COVID-19 vaccinations for their children

It is important to encourage parental acceptance of children’s vaccination against COVID-19 to ensure population immunity and mitigate morbidity and mortality. This study drew upon protection motivation theory (PMT) to explore the factors of parental hesitancy about vaccinating their children. A national online survey was performed in China. A total of 2054 Chinese parents of children aged 6–12 years were included in this study. They reported on measures that assessed hesitancy about children’s vaccination against COVID-19, PMT constructs (susceptibility, severity, response efficacy, self-efficacy, and response costs) and sociodemographic characteristics. Chinese parents reported a hesitancy rate of 29.4% for children’s vaccination. Parents with higher level education were more likely to hesitate to vaccinate their children against COVID-19. After controlling for parents’ and children’s demographic variables, logistic regression showed that parents’ hesitancy about their children’s vaccination increased if parents had lower levels of susceptibility, response efficacy or self-efficacy, as well as higher levels of response costs. In addition, a high educational level can significantly increase the promotive effect of response cost and the protective effect of response efficacy on vaccine hesitancy. In conclusion, our findings suggested that PMT can explain parents' vaccine hesitancy and that education level can modify the effect of copying appraisal, but not threat appraisal, on parental hesitancy. This study will help public health officials send targeted messages to parents to improve the rate of COVID-19 vaccination in children aged 6–12 years and thus reach a higher level of immunity in the population.     

Under-explored assumptions in influenza vaccination models: Implications for the universal vaccination of children

The aim of this study was to explore several important (but uncertain) assumptions in influenza models which affect the estimated benefits of vaccination programs. We combined consideration of these factors with the seasonal variability of influenza transmissibility to gain a better understanding of how they may influence influenza control efforts. As our case study, we considered the potential impact of universal seasonal childhood vaccination in Australia using a simplified age-stratified Susceptible Exposed Infectious Recovered (SEIR) model to simulate influenza epidemics and the impact of vaccination. We found that the choice of vaccine efficacy model was influential in determining the impact of vaccination. This choice interacted with other model assumption such as those around the infectiousness of asymptomatic cases and the match of the vaccine to the circulating strains. The methodological approach used to estimate influenza hospitalisations was also highly influential. Our study highlights the role that key modelling assumptions play when estimating the impact of vaccination against influenza.