Low rates of influenza vaccination uptake among healthcare workers: Distinguishing barriers between occupational groups

Vaccination coverage of primary care providers against seasonal influenza, tetanus, pneumococcal pneumonia and herpes zoster: A cross-sectional study in Greece

Introduction

Primary care providers' (PCPs) compliance to self-immunization is important for their protection and the protection of their colleagues and patients and has been associated with the coverage of the general public. In this study, we aim to investigate the vaccination coverage of PCPs.

Methods

A questionnaire-based cross-sectional survey was conducted among physicians, nurses and pharmacists employed in public or private primary care settings in Greece. Demographic and occupational characteristics as well as vaccination coverage data for influenza, tetanus, pneumococcal pneumonia and herpes zoster were collected. Statistical significance was set at 0.05.

Results

In total, 748 (61.7% response rate) PCPs participated. Vaccination rates were 66.4% (496/747) for influenza (2019/2020 flu season), 62.9% (469/746) for tetanus (10-year Td or Tdap booster dose), 70% (14/20) for pneumococcal pneumonia (≥ 1 dose of PPSV23 or PCV13) and 12.3% (10/81) for herpes zoster. Multiple logistic regression revealed that nurses had significantly lower probability of being vaccinated against influenza [odds ratio (OR) = 0.25; 95% confidence interval (CI) = 0.14-0.45] and pharmacists had significantly lower probability of being vaccinated against both influenza (OR = 0.44; 95% CI = 0.31-0.62) and influenza & tetanus (OR = 0.52; 95% CI = 0.37-0.73) compared to physicians. Older age (>40 years) was an independent risk factor for not receiving a tetanus vaccine (40-49 vs. 19-39; OR = 0.42; 95% CI = 0.28-0.63, over 50 years old vs. 19-39; OR = 0.54; 95% CI = 0.36-0.79).

Conclusions

The results revealed suboptimal vaccination rates among health providers who are in the frontline of adult immunization. Individualized and targeted measures to improve their vaccination coverage and indirectly the vaccination coverage of their patients, are therefore required.

Recipient-Reported Reactogenicity of Different SARS-CoV-2 Vaccination Regimens among Healthcare Professionals and Police Staff in Germany

The rapid availability of effective vaccines against SARS-CoV-2 was key during the COVID-19 pandemic. However, vaccine hesitancy and relatively low vaccine coverage rates among the general population and particularly vulnerable populations such as healthcare staff reduced the potential benefits of these vaccines. During the early phase of the pandemic, fear of vaccine-related adverse events was common among individuals who refused vaccination. Between March and May 2021, we comparatively assessed the self-reported reactogenicity of different SARS-CoV-2 prime-boost regimens using mRNA-based (BNT162b2 and mRNA-1273) and vector-based vaccines (ChAdOx1 nCoV-19) in (a) healthcare workers (HCW), and (b) police staff from southwest Germany. The majority of participants (71.8%; 1564/2176) received a homologous vaccination. Among HCW, 75.0% were female, whereas 70.0% of police staff were male. The most frequently reported reactions following the first vaccine administration were pain at the injection site (77.94%; 1696/2176), tiredness (51.75%; 1126/2176), and headache (40.44%; 880/2176), which were more commonly reported by HCW as compared to police staff. In homologous, mRNA-based and heterologous vaccination schedules, more reactions were reported after the second vaccine dose. We conclude that the frequency and intensity of self-perceived vaccine reactogenicity may differ between specific population groups and might be mitigated by tailored communication strategies.

Towards a less voluntary vaccination policy in the Netherlands? Findings from an expert interview study

BACKGROUND

The Netherlands traditionally favours a voluntary approach to vaccination. However, during the COVID-19 pandemic multiple European countries drastically altered their vaccination policies, which fuelled societal and political debate about the need to make the Dutch vaccination policy less voluntary, particularly by utilising pressure or coercion.

AIM

To provide insight in expert's views on main normative issues concerning a less voluntary vaccination policy (for adults). Our study adds to the existing debate by addressing this topic from a multidisciplinary viewpoint.

METHODS

We conducted 16 semi-structured interviews with legal, medical and ethical experts on the Dutch vaccination policy, between November 2021 and January 2022. We analysed interview transcripts through inductive coding.

RESULTS

Most experts believe a less voluntary vaccination policy is of added value under certain circumstances, as exemplified by the outbreak of COVID-19. For such a policy, a legislative approach might be most effective. However, different views exist on the desirability of a less voluntary approach. Main arguments in favour are based on epidemiological circumstances and a duty towards the collective health interest, whilst arguments against are based on the questionable necessity and adverse effectiveness of such policy.

CONCLUSIONS

If implemented, a less voluntary vaccination policy should be context-specific and take into account proportionality and subsidiarity. It is recommendable for governments to embed such policy (a priori) in flexible legislation.

Pharmacists' attitudes toward influenza vaccination: does the COVID-19 pandemic make a difference?

Background

Influenza vaccine uptake in most European countries remains low, despite the World Health Organization's target of 75%. Community pharmacists play a vital role in promoting vaccination; however, they have been reported to be vaccine-hesitant. This study aimed to investigate changes in pharmacists' attitudes toward influenza vaccination since the onset of the COVID-19 pandemic, as well as their COVID-19 vaccination intentions.

Methods

In December 2020, all members of the Swiss Association of Pharmacists were invited to participate in an online, cross-sectional survey. This study assessed pharmacists' attitudes toward influenza vaccination by surveying influenza vaccine uptake during the 2019-20 influenza season and possible reasons for their decision(s), in addition to their intention to receive COVID-19 and seasonal influenza vaccination(s) during the 2020-21 influenza season. Descriptive analysis and multinomial logistic regression were used to assess predictors of vaccine uptake and intention.

Results

Of 5900 Swiss pharmacists, 569 (9.6%) completed the survey. The self-reported influenza vaccination coverage among pharmacists during the 2019-20 season was 48.0%. The primary reason for vaccine uptake was the belief that all healthcare workers should be vaccinated, whereas the main reason for refusal was a lack of concern about contracting influenza. The proportions of participants who intend to accept influenza and COVID-19 vaccinations in the 2020-2021 season, when available, were 63.3% and 66.5%, respectively. The most important predictor of high willingness to be vaccinated against influenza in 2020-21 was vaccination history (OR = 3.73; 95% CI = 1.47-9.50), while the most critical predictor of willingness to be vaccinated against COVID-19 was the intention to be vaccinated against influenza (OR = 3.45; 95% CI = 1.74-6.84).

Conclusions

Findings indicated that although pharmacists' readiness to accept seasonal influenza vaccination significantly increased during the COVID-19 pandemic, influenza vaccine uptake among them remains suboptimal. This is consistent with what has been reported in the literature.

Low influenza vaccine uptake by healthcare workers caring for the elderly in South African old age homes and primary healthcare facilities

BACKGROUND

The elderly bear the highest burden of South Africa's estimated annual > 10 million influenza cases and > 11,000 influenza-related deaths. Unvaccinated healthcare workers (HCWs) are at high occupational risk of contracting influenza, and may transmit influenza to elderly patients in their care. Thus, the South African National Department of Health recommends that HCWs receive annual influenza vaccination. This study aimed to determine influenza vaccination coverage among HCWs; identify reasons for their vaccination status; and investigate if HCWs recommend vaccination to their elderly patients.

METHODS

A descriptive study was conducted in 18 community health centres and 44 private sector and non-governmental organisation managed old age homes across South Africa, using a self-administered structured questionnaire, which was distributed to 360 HCWs present on the day of data collection. Data were captured using Microsoft Excel® and imported to Epi Info™ 7 (Centers for Disease Control and Prevention, USA) for descriptive statistical analysis. Ethics approval (SMUREC/P/36/2018: PG) and permission to conduct the study at the facilities were obtained. All participants provided informed consent.

RESULTS

The response rate was 76.7% (276/360). Most participants were female (90.9% [251/276]), nursing professionals (81.2% [224/276]) with a mean age of 41.1 ± 11.7 years. Although 62.7% of participants indicated having ever received at least one dose of the influenza vaccine, influenza vaccine uptake for 2017 and 2018 was 24.36% (41/276) and 33.3% (92/276) respectively. The main reasons given for never being vaccinated against influenza were related to the unavailability of the vaccine (70.9%) and vaccine hesitancy (27.2%). Most participants (67.8% [187/276]) recommended vaccines to elderly patients in their care.

CONCLUSION

The main reasons behind low influenza vaccine uptake by HCWs in South Africa who care for the elderly were related to unavailability of the vaccine and vaccine hesitancy. Strategies to educate HCWs on the importance of influenza vaccination, while concurrently increasing sustained and easy access to the vaccine by HCWs are needed to preserve public health.

Factors influencing healthcare professionals' confidence in vaccination in Europe: a literature review

Health-care professionals (HCPs) have a fundamental role in vaccination, their own beliefs and attitudes affecting both their uptake and recommendation of vaccines. This literature review (n = 89) summarises evidence on HCPs’ perceptions of the risks and benefits of vaccination, trust, and perceptions of mandatory vaccination in Europe. HCPs across studies believed that vaccination is important to protect themselves and their patients. However, beliefs that some diseases such as influenza are less risky were reported by some HCPs as a reason for not getting vaccinated. Concerns about both short- and long-term side effects were identified among HCPs in most studies, such as those affecting the immune or neurological system. Mistrust toward health authorities and pharmaceutical industry was reported in some studies. The question of mandatory vaccination revealed mixed opinions, with some favoring self-determination and others viewing vaccination as a duty. This review highlights key factors influencing HCPs’ confidence in vaccination in Europe.

A mixed methods study of health care professionals’ attitudes towards vaccination in 15 countries

Background

Health care professionals are widely considered to be the most trusted source of information on vaccine-related topics. However, several are reporting their own hesitancy around certain vaccines, influencing their intention to vaccinate themselves as well as influencing their recommendations to their patients and target population.

Methods

A mixed-methods approach was used including an online survey (n = 1,504) in 15 countries which aimed to determine drivers of HCPs vaccine confidence and examine how these drivers vary across nations. Thirty in-depth semi-structured interviews were conducted with 10 HCPs in a subset of three countries (France, Greece and Hungry) to explore barriers to HCPs vaccine uptake and their role in addressing vaccine hesitancy among patients.

Findings.

The survey’s regression analysis identified that nurses/midwives and HCPs from Hungary, Italy, Romania and Switzerland were less confident in the safety, importance or effectiveness of vaccines in general. Morocco (35%), Turkey (53%) and Greece (69%) reported the lowest influenza vaccination coverage among HCPs. Morocco also reported the lowest rates of HCPs who were “highly likely” to recommend MMR vaccine (34%), HPV vaccine (31%) and Covid-19 vaccines (29%). More than third of HCPs reported a lack of trust in health authorities and in the information they provide. Thematic analysis revealed that concerns over the risk of side-effects associated with vaccines, preference for natural immunity, whether it was necessary to be vaccinated against influenza every year, not having any chronic disease risk factors, and vaccines mandates as the key barriers to HCPs vaccination against influenza and Covid-19.

Conclusion

HCPs have an important role in vaccination and their confidence in vaccination and health authorities must be improved as this may affect their uptake of vaccines and influence their recommendations to their patients. Investigating the impact of political, socio-economic and cultural contexts on concerns about vaccination among HCPs is also necessary.

Medical screening tests and vaccination among hospital-based physicians in Israel

Background

Very few studies have evaluated physician participation in screening tests and vaccinations. The aim was to evaluate attitudes and actual practice of screening tests and vaccinations among hospital-based physicians and to identify factors that predict actual performance.

Methods

A cross-sectional study including 220 physicians in various specializations. The study was conducted between January 1, 2017 and December 10, 2017. The statistical analysis was performed during October, 2020 and completed in October 25, 2020.

Results

The vast majority of physicians (94%) believed in the importance of screening tests for physicians, but less than half actually underwent the tests themselves. A high percentage of physicians measured their BMI (84.5%) and had a serum lipid profile test (67.7%) and complete blood counts (75%) over the previous five years, but less than a third of female physicians over 50 years of age had a mammogram and only 8% of the physicians over 50 had a fecal occult blood test. A high percentage of physicians were vaccinated for Hepatitis A and B, chickenpox and measles (66-96% for the various vaccinations), but only 41% had an influenza vaccination in the previous year. In a multivariate logistic regression model, physicians who believed that hospital physicians bore a responsibility for recommending screening tests to their patients were more likely to have their BMI and their blood pressure checked (OR = 2.234, P = 0.007). They were more likely to undergo laboratory testing (OR = 4.082, P < 0.0001) and tended to get vaccinated more (OR = 1.907, P = 0.051).

Conclusion

The rate of screening tests and vaccinations among hospital-based physicians is sub-optimal and very low for fecal occult blood testing and mammograms. Structured programs are required to implement screening tests and vaccinations among physicians.

Monitoring influenza vaccination coverage among healthcare workers during the COVID-19 pandemic: a three-year survey in a large university hospital in North-Western Italy

INTRODUCTION

Healthcare workers (HCWs) are one of the highest priority groups recommended for seasonal influenza vaccination (SIV). Greater awareness of the importance of influenza vaccination was observed among HCWs after the start of the COVID-19 pandemic. The aim of this study was to analyze SIV coverage rates in the 2019-2020, 2020-2021 and 2021-2022 seasons among HCWs employed at the IRCCS Ospedale Policlinico San Martino in Genoa, in order to observe how coverage has changed since the COVID-19 pandemic began.

METHODS

A retrospective, single-center study was conducted among HCWs working at the IRCCS Ospedale Policlinico San Martino in Genoa. The vaccinated population was stratified by gender, age, qualification and area of activity, and the characteristics of vaccinated HCWs were analyzed.

RESULTS

While SIV coverage was below the recommended target in all seasons, a sharp increase was observed in 2020/2021 (12.8%; 40.9% and 23% in 2019/2020, 2020/2021 and 2021/2022, respectively). The mean and median age of vaccinees also increased during the 2020/2021 vaccination campaign (46.7 and 49 years, respectively) in comparison with the 2019/2020 season (43.5 and 45, respectively). In the 2019/2020 and 2021/2022 seasons, a higher proportion of vaccinees were physicians. Vaccinated females outnumbered males, but the coverage rate resulted greater in males than females in all three seasons. While a higher proportion of vaccinated subjects worked in medical areas, the most evident increase over the three years was seen among subjects working in the services area.

CONCLUSIONS

This survey highlights the importance of studying the determinants that influence vaccination adherence and how the COVID-19 pandemic has affected SIV coverage.

Seasonal Influenza Vaccination at a German University Hospital: Distinguishing Barriers Between Occupational Groups

The annual influenza vaccination has been officially recommended for medical staff in Germany since 1988. Nevertheless, the vaccination rate among medical staff is still low. The present study deals with the influenza vaccination rate of staff at a German University hospital over time as well as with the reasons that led to a positive vaccination decision and the barriers to acceptance of vaccination. For this purpose, the staff members received questionnaires in which they were asked about influenza vaccination and the reasons for or against vaccination. In addition, the questionnaire contains information on gender, age group, occupational group and presence of a chronic co-morbidity. Logistic regression analysis was used to investigate which of these predictors most strongly influenced the vaccination decision. It was shown that the reasons for or against vaccination differ significantly between the occupational groups and that the occupational group affiliation has the greatest influence on the vaccination decision in the comparison of the investigated predictors. In order to achieve a positive influence on vaccination acceptance, future measures should focus on increasing confidence in vaccination and on increasing the perception of risk from influenza illness. The findings may contribute to future targeted strategies to increase vaccination rates and suggest occupational group-specific interventions.

Vaccination against influenza among Lebanese health care workers in the era of coronavirus disease 2019

Background

Health-care workers (HCWs) are at a higher occupational risk of contracting and transmitting influenza. Annual vaccination is an essential tool to prevent seasonal influenza infection. However, HCWs vaccine hesitancy remains a leading global health threat. This study aims to evaluate the flu vaccination coverage rates among Lebanese HCWs and to assess their knowledge, attitudes, practices, perceived barriers, and benefits toward the flu vaccine during the COVID-19 pandemic. In addition, we sought to identify the factors associated with flu vaccine uptake.

Methods

A cross-sectional study using an online survey was conducted in Lebanon among HCWs between 14 and 28 October 2020. Multivariable logistic regression was carried out to identify the factors associated with influenza vaccine uptake.

Results

A total of 560 HCWs participated in the survey of whom 72.9% were females, and 53.9% were aged between 30-49 years. Regarding Flu vaccination uptake, the rate has risen from 32.1% in 2019-2020 to 80.2% in 2020-2021 flu season. The majority of HCWs had a good knowledge level and a positive attitude toward flu vaccination. Regarding their practices, less than 50% of HCW were currently promoting the importance of getting the flu vaccine. The majority (83.3%) ranked the availability of a sufficient quantity of vaccines as the most significant barrier to flu vaccination. The main perceived flu vaccination benefits were enhancing patient safety, minimizing the viral reservoir in the population, decreasing hospital admission, and avoiding influenza and COVID-19 co-infection. The odds of influenza vaccine uptake was lower in unmarried compared to married HCWs (OR = 0.527, CI (0.284-0.978). However, HCWs having received the influenza vaccine in the previous season (OR = 6.812, CI (3.045-15.239)), those with good knowledge level (OR = 3.305, CI (1.155-9.457)), low perceived barriers (OR = 4.130, CI (1.827-9.334)) and high perceived level of the benefits (OR = 6.264, CI (2.919-13.442)) of the flu vaccination were found more prone to get the flu vaccine.

Conclusion

Flu vaccination uptake has increased among HCWs during the 2020-2021 flu season compared with the previous one. Continuing education as well as ensuring free, equitable, and convenient access to vaccination are still required to increase the annual flu vaccination uptake among HCWs.

Adverse events following influenza immunization: understanding the role of age and sex interactions

BACKGROUND

Reduction of adverse events following immunization (AEFI) could improve vaccine uptake. Evidence suggests sex and age affect AEFI rates but, with limited understanding of their interaction, groups at higher risk for adverse reaction cannot be identified.

RESEARCH DESIGN AND METHODS

Using deidentified data (n = 308,481) from Australians receiving influenza vaccinations in the 2020 calendar year, we analyzed the effects of independent predictors (i.e. age and sex), on experiencing an AEFI using logistic regression generalized additive modeling to capture any nonlinear relationships and adjusting for vaccine brand and concomitant vaccination.

RESULTS

The overall reaction rate was 5.5%. Modeling revealed significant effects of age (p < 0.001), sex (p < 0.001), and age × sex (p < 0.001). Females were more likely than males to experience AEFIs between 7.5 and 87.5 years of age and exhibited peak odds at about 53 years, while peak odds for males occurred in infancy.

CONCLUSION

The results suggest there is a need for targeting AEFI reduction in females, particularly in 30-70-year-olds, to improve the vaccination experience. The results further suggest that reducing concomitant vaccination and choosing less reactogenic vaccine brands could reduce risk of AEFI, however, retaining concomitant vaccination may optimize vaccine uptake.

Knowledge, attitudes and practices related to influenza and influenza vaccine among healthcare workers in Chongqing, China-a cross-sectional study

Influenza is associated with a substantial disease burden, and influenza vaccination is recommended to all healthcare workers. We aimed to assess healthcare workers' knowledge, attitudes, and practices about influenza and its vaccine in Chongqing, China. A cross-sectional study was conducted at selected hospitals from September to November 2019, in which healthcare workers filled in a self-administered questionnaire. Both sentinel (42.92%) and non-sentinel hospitals (57.08%) were included. The majority were nurses (52.48%) and physicians (32.37%). Half (50.42%) of the respondents had a good command of knowledge, and the proportion of healthcare workers having a positive attitude accounted for 62.68%. The primary information sources were colleagues (58.81%), followed by television, newspapers and media (30.18%). The number of healthcare workers reported having got vaccinated last year was only 237 (16.78%), and the main reason was protecting themselves from influenza (93.25%). While the most common reasons given for not getting vaccinated were having no time (65.70%), believing it is unnecessary to get vaccinated (29.62%), worrying about the quality of influenza vaccine (27.49%) or the adverse reactions (25.70%). Factors associated with self-reported high vaccination were sentinel hospital (aOR: 1.427; 95% CI: 1.057-1.925), high-risk department (aOR: 1.919; 95% CI: 1.423-2.589), positive attitude (aOR: 2.429; 95% CI: 1.697-3.477) and taking the initiative to learn influenza information (aOR: 3.000; 95% CI: 1.983-4.538). We concluded that healthcare workers in Chongqing had some misconceptions although many of them showed a positive attitude toward the influenza vaccine. Various strategies, including educational training and on-site vaccination, are necessary to improve the knowledge and overall vaccination coverage.

Evaluation of Flu Vaccination Coverage among Healthcare Workers during a 3 Years' Study Period and Attitude towards Influenza and Potential COVID-19 Vaccination in the Context of the Pandemic

(1) Background: vaccination of healthcare workers (HCWs) against seasonal influenza is considered the most effective way to protect HCWs, ensure patient's safety and to maintain essential health care services during influenza epidemics. With the present study we aimed to evaluate the efficacy of incremental bundles of measures implemented during the last three flu campaigns and to assess the attitudes towards influenza vaccination and a potential vaccine against COVID-19 among HCWs, in a large university hospital in Pisa, Italy. (2) Methods: We described measures implemented during 2018/2019, 2019/2020 and 2020/2021 and assessed their impact on flu vaccine coverage (VC) among employees and residents in Pisa university hospital. We considered sex, profession and ward to investigate differences in uptake. In addition, in 2020 a survey was developed and distributed to all employees to evaluate flu and COVID-19 vaccines attitudes. (3) Results: during the 2018/19 and 2019/20 flu campaigns the overall VC rate among HCWs was, respectively, 10.2% and 11.9%. In 2020/21 the overall VC rate jumped to 39.3% (+ 230.6%). Results from the survey indicated a more positive attitude towards flu vaccine as compared to COVID-19 vaccines among the 10.6% of the staff members who responded to the survey. In addition, 70.97% of HCWs totally agreed that being vaccinated against influenza would be more important than the previous years because of COVID-19 emergency. (4) Conclusions: a significant increase in VC was observed in 2020/21, especially among those sub-groups with consistently lower uptake in previous years. The COVID-19 pandemic positively influenced flu vaccination uptake during the 2020/21 season.

Attitudes of Healthcare Personnel towards Vaccinations before and during the COVID-19 Pandemic

Vaccines constitute highly effective tools for controlling and eliminating vaccine-preventable diseases (VPDs) and are assessed to avert between two to three million deaths per year globally. Healthcare personnel (HCP) constitute a priority group for several vaccinations. However, studies indicate significant rates of vaccine hesitancy among them and, therefore, of acceptance of vaccination recommendations. This cross-sectional study was conducted in a university hospital in Southern Italy to assess the knowledge and attitudes of HCP about VPDs before and during the COVID-19 pandemic, estimate their intention to get vaccinated against COVID-19, and search for determinants that may influence their choice. A self-administered questionnaire was used. HCP improved their knowledge about VPDs and were more favorable to vaccinations in September–December 2020 compared to January–December 2019. Overall, 75% of respondents would get a COVID-19 vaccine. Our findings indicate a potential role of the ongoing COVID-19 pandemic on Italian HCP’s knowledge and attitudes towards vaccines.

Insights into the protective effects of influenza vaccination: More hospitalizations but lower follow-up mortality during the 2014/15 influenza season in a Swiss cohort

BACKGROUND

Observational studies of influenza vaccination are criticized as flawed due to unmeasured confounding. The goal of this cohort study was to explore the value and role of secondary claims data to inform the effectiveness of influenza vaccination, while systematically trying to reduce potential bias.

METHODS

We iteratively reviewed the components of the PICO approach to refine study design. We analyzed Swiss mandatory health insurance claims of adult patients with chronic diseases, for whom influenza vaccination was recommended in 2014. Analyzed outcomes were all-cause mortality, hospitalization with a respiratory infection or its potential complication, and all-cause mortality after such hospitalization, adjusting for clinical and health care use variables. Cox and multi-state models were applied for time-to-event analysis.

RESULTS

Of 343,505 included persons, 22.4% were vaccinated. Vaccinated patients were on average older, had more morbidities, higher health care expenditures, and had been more frequently hospitalized. In non-adjusted models, vaccination was associated with increased risk of events. Adding covariates decreased the hazard ratio (HR) both for mortality and hospitalizations. In the full model, the HR [95% confidence interval] for mortality during season was 0.82 [0.77-0.88], and closer to null effect after season. In contrast, HR for hospitalizations was increased during season to 1.28 [1.15-1.42], with estimates closer to null effect after season. HR in multi-state models were similar to those in the single-outcome models, with HR of mortality after hospitalization negative both during and after season.

CONCLUSION

In patients with chronic diseases, influenza vaccination was associated with more frequent specific hospitalizations, but decreased risk of mortality overall and after such hospitalization. Our approach of iteratively considering PICO elements helped to consider various sources of bias in the study sequentially. The selection of appropriate, specific outcomes makes the link between intervention and outcome more plausible and can reduce the impact of confounding.