The effects of influenza vaccination of health care workers in nursing homes: insights from a mathematical model

Background

Annual influenza vaccination of institutional health care workers (HCWs) is advised in most Western countries, but adherence to this recommendation is generally low. Although protective effects of this intervention for nursing home patients have been demonstrated in some clinical trials, the exact relationship between increased vaccine uptake among HCWs and protection of patients remains unknown owing to variations between study designs, settings, intensity of influenza seasons, and failure to control all effect modifiers. Therefore, we use a mathematical model to estimate the effects of HCW vaccination in different scenarios and to identify a herd immunity threshold in a nursing home department.

Methods and Findings

We use a stochastic individual-based model with discrete time intervals to simulate influenza virus transmission in a 30-bed long-term care nursing home department. We simulate different levels of HCW vaccine uptake and study the effect on influenza virus attack rates among patients for different institutional and seasonal scenarios. Our model reveals a robust linear relationship between the number of HCWs vaccinated and the expected number of influenza virus infections among patients. In a realistic scenario, approximately 60% of influenza virus infections among patients can be prevented when the HCW vaccination rate increases from 0 to 1. A threshold for herd immunity is not detected. Due to stochastic variations, the differences in patient attack rates between departments are high and large outbreaks can occur for every level of HCW vaccine uptake.

Conclusions

The absence of herd immunity in nursing homes implies that vaccination of every additional HCW protects an additional fraction of patients. Because of large stochastic variations, results of small-sized clinical trials on the effects of HCW vaccination should be interpreted with great care. Moreover, the large variations in attack rates should be taken into account when designing future studies.     

禽流感的历史和公共卫生意义

简要介绍了禽流感的历史,在我国的流行现状,危害,与其动物流感的关系及公共卫生意义。     

The oral health of individuals with dementia in nursing homes

Objective: To determine if moderate to severe dementia has an effect on the oral health of individuals resident in nursing homes. Background: A significant proportion of the elderly population lives in nursing homes and suffers from varying degrees of dementia. Dementia might affect an individual's ability to implement oral care. Previous work in this area has focused on individuals with mild dementia living in the community setting. Material and methods: Two matched cohorts of subjects resident in four nursing homes in Cheshire were recruited (n = 135). One cohort's subjects were deemed to have no or mild dementia, whereas the other cohort's subjects were deemed to have moderate to severe dementia. Oral parameters were scored, including Decayed, Missing, Filled Teeth (DMFT) scoring, dental deposit scoring, denture assessment and the noting of any other pathology. Results: There was a statistically significant difference in the relative level of dementia of the subjects between the two cohorts (p < 0.01, Student's t‐test). The DMFT scores were similar for both groups. The mean number (±SD) of decayed and missing teeth for the no/mild dementia group was 1.11 (±3.42) and 28.22 (±6.64), whilst that of the moderate/severe dementia cohort was 0.80 (±1.87) and 27.28 (±7.73), respectively. Eleven per cent of the moderate/severe dementia cohort wore an upper denture alone as compared with 16% in the no/mild dementia group. Conclusion: For individuals resident in nursing homes, moderate to severe dementia might have a deleterious effect on oral health. Further work in this area is required.     

Seasonal influenza vaccination campaigns for health care personnel: systematic review

Background

In Canada, vaccination coverage for seasonal influenza among health care personnel remains below 50%. The objective of this review was to determine which seasonal influenza vaccination campaign or campaign components in health care settings were significantly associated with increases in influenza vaccination among staff.

Methods

We identified articles in eight electronic databases and included randomized controlled trials, controlled before-and-after studies and studies with interrupted time series designs in our review. Two reviewers independently abstracted the data and assessed the risk of biases. We calculated risk ratios and 95% confidence intervals for randomized controlled trials and controlled before-and-after studies and described interrupted time series studies.

Results

We identified 99 studies evaluating influenza vaccination campaigns for health care workers, but only 12 of the studies were eligible for review. In nonhospital health care settings, including long-term care facilities, campaigns with a greater variety of components (including education or promotion, better access to vaccines, legislation or regulation and/or role models) were associated with higher risk ratios (i.e, favouring the intervention group). Within hospital settings, the results reported for various types of campaigns were mixed. Many of the criteria for assessing risk of bias were not reported.

Interpretation

Campaigns involving only education or promotion resulted in minimal changes in vaccination rates. Further studies are needed to determine the appropriate components and combinations of components in influenza vaccination campaigns for health care personnel.Health care personnel can act as vectors of influenza and may transmit the disease to patients who are at risk for influenza-related complications or death.¹ A Cochrane review² of three studies showed that vaccination of health care personnel, combined with vaccination of patients, was 86% efficacious (95% confidence interval [CI] 40%–97%) in preventing influenza-like illnesses among elderly patients. It is recommended that all health care personnel (i.e., minimum 90% coverage) receive the seasonal influenza vaccine for protection from the virus.³Rates of vaccination against seasonal influenza among health care personnel are often below targeted levels and vary across health care organizations in Canada and internationally. In 2003, vaccination coverage was 46% among Canadians employed in ambulatory care settings, hospitals and long-term care facilities.⁴ In a survey of Canadian long-term care facilities, the average vaccination rate among workers was 35%.⁵ Similarly, in the United States, vaccination coverage for health care personnel was about 40%,⁶ and in European countries, reported vaccine uptake has ranged from 14% to 48%.⁷The Canadian National Advisory Committee on Immunization encourages all organizations to actively promote the influenza vaccine and to provide education aimed at health care personnel.³ The US Healthcare Infection Control Practices Advisory Committee and the Advisory Committee on Immunization Practices have recommended that all organizations employing health care personnel use evidence-based approaches that may overcome barriers to vaccine uptake as part of their influenza vaccination campaigns.⁶ These two committees identified five categories of components of influenza vaccination campaigns aimed at improving immunization rates among health care personnel (6

Spatial considerations for the allocation of pre-pandemic influenza vaccination in the United States

The impact of the next influenza pandemic may be mitigated by inducing immunity in individuals prior to the start of national epidemics using a pre-pandemic vaccine targeted against current avian influenza strains. The US Department of Health and Human Services (HHS) intends that pre-pandemic vaccines will be allocated to states in proportion to the size of their population in predefined priority groups, i.e. approximately pro-rata. We show that such an equitable policy is likely to be the least efficient in terms of the number of infections averted. We demonstrate that the potential benefits could be substantial if a fully discretionary policy is allowed, i.e. if some regions are allocated sufficient vaccines to achieve herd immunity while other regions are allocated no vaccine. Since such an inequitable policy may be impractical, we consider the sensitivity of an intermediate policy (in which 50% of the stockpile is allocated on a pro-rata basis) to key transmission uncertainties. The benefits of the 50% discretionary policy are sensitive to parameter values which cannot be known in advance. Therefore, despite substantial potential benefits of non-pro-rata policies, our results suggest that the current HHS policy of pro-rata allocation by state is a good compromise in terms of simplicity, robustness, equity and efficiency.     

Individual discrimination capability and collective decision-making

Amplification is the main component of many collective phenomena in social and gregarious insects. In a society, individuals face a mixed palette of odours coming from different groups (lines, strains) and individuals present discrimination capabilities. However, often at the collective level, different groups may cooperate and act together. To understand this apparent contradiction, we use a model of food recruitment where each group of foragers have its own blend of pheromone trail that is partly recognized by the others groups. The model shows that a low level of recognition between signals is sufficient to produce a collaborative pattern between groups and that beyond a critical value of recognition, only the aggregation of all the groups around the same food source is observed. The comparison between this model and one describing the site selection by gregarious insects (e.g. cockroach) suggests that such collective response is a generic property of social phenomena governed by amplification processes.     

The social network around influenza vaccination in health care workers: a cross-sectional study

Background

Influenza vaccination coverage remains low among health care workers (HCWs) in many health facilities. This study describes the social network defined by HCWs’ conversations around an influenza vaccination campaign in order to describe the role played by vaccination behavior and other HCW characteristics in the configuration of the links among subjects.

Methods

This study used cross-sectional data from 235 HCWs interviewed after the 2010/2011 influenza vaccination campaign at the Hospital Clinic of Barcelona (HCB), Spain. The study asked: “Who did you talk to or share some activity with respect to the seasonal vaccination campaign?” Variables studied included sociodemographic characteristics and reported conversations among HCWs during the influenza campaign. Exponential random graph models (ERGM) were used to assess the role of shared characteristics (homophily) and individual characteristics in the social network around the influenza vaccination campaign.

Results

Links were more likely between HCWs who shared the same professional category (OR 3.13, 95% CI?=?2.61–3.75), sex (OR 1.34, 95% CI?=?1.09–1.62), age (OR 0.7, 95% CI?=?0.63–0.78 per decade of difference), and department (OR 11.35, 95% CI?=?8.17–15.64), but not between HCWs who shared the same vaccination behavior (OR 1.02, 95% CI?=?0.86–1.22). Older (OR 1.26, 95% CI?=?1.14–1.39 per extra decade of HCW) and vaccinated (OR 1.32, 95% CI?=?1.09–1.62) HCWs were more likely to be named.

Conclusions

This study finds that there is no homophily by vaccination status in whom HCWs speak to or interact with about a workplace vaccination promotion campaign. This result highlights the relevance of social network analysis in the planning of health promotion interventions.

     

Incidence of amantadine-resistant influenza A viruses in sentinel surveillance sites and nursing homes in Niigata, Japan

We surveyed the incidence of amantadine-resistant influenza A viruses both at sentinel surveillance sites and at nursing homes, and verified their types of change by partial nucleotide sequence analysis of the M2 protein. Fifty-five influenza A viruses from 27 sentinel surveillance sites during six influenza seasons from 1993 to 1999, and 26 influenza A viruses from 5 nursing homes from 1996 to 1999 were examined for susceptibility to the drug by virus titration in the presence or absence of amantadine. While amantadine-resistant viruses were not found in sentinel surveillance sites, a high frequency of resistance (8/26, 30.8%) in nursing homes was observed. Resistant viruses can occur quickly and be transmitted when used in an outbreak situation at nursing homes, where amantadine is used either for neurologic indications or for influenza treatment. Eight resistant viruses had a single amino acid change of the M2 protein at residue 30 or 31. In vitro, all 11 sensitive viruses turned resistant after 3 or 5 passages in the presence of 2 microg/ml amantadine, and they showed an amino acid change at residue 27, 30, or 31. The predominant amino acid substitution in the M2 protein of resistant viruses is Ser-31-Asp (a change at 31, serine to asparagine). The results indicate that a monitoring system for amantadine-resistant influenza viruses should be established without delay in Japan.