Protective Effect Of Influenza Vaccination Research Articles

Abstract 524: Influenza Vaccination Reduces The Risk Of Venous Thromboembolism

It is widely accepted that influenza vaccination reduces the risk of cardiovascular events in patients with coronary artery diseases. However, no information is available concerning the role of influenza vaccination in venous thromboembolism (VTE). Methods: A case-control study was conducted in 727 cases and 727 age and sex-matched controls from 11 centers in France (the FARIVE study). Cases were patients with a first documented episode of VTE and without any personal history of cancer within the last 5 years; controls were recruited in the same hospital and had no personal history of venous or arterial thrombosis. Results: Overall, 202 (28.2%) of cases and 233 (32.1%) of controls had influenza vaccination during the previous 12 months at the time of recruitment. Information was not available for only 12 subjects out of 1454. The crude odds ratio (OR) for VTE associated with influenza vaccination was 0.76 (95% CI 0.58–0.99). After adjustment for potential confounding variables (age, sex, inclusion date, BMI, educational levels and varicose veins), the OR for VTE associated with vaccination was 0.74 (95% CI 0.57–0.97). The protective effect of vaccination toward VTE was higher in the population below 52 years (median of age), with an OR of 0.52 (95% CI 0.32–0.85). In women below the age of 51, the crude OR for VTE associated with influenza vaccination was 0.50 (95% CI 0.24–1.05) and was significant after adjustment for confounding variables including oral contraceptives, with an OR of 0.41 (95% CI 0.19–0.92). The protective effect of vaccination was similar for different types of VTE (DVT or PE). There was no statistical differences in the protective effects when we compared provoked with unprovoked VTE events. Conclusion: This is the first study that demonstrates a protective effect of influenza vaccination in VTE. In vitro influenza induces activation of coagulation and inflammation but we cannot rule out that the protective effect of influenza vaccination was due to other unknown mechanisms, as the protective effect was similar within the different seasons of the year. Influenza vaccination may reduce the risk of VTE by 26%. This relationship between influenza vaccination and VTE and its underlying mechanism still need to be analyzed and confirmed in further studies.

Selection bias in evaluating of influenza vaccine effectiveness: A lesson from an observational study of elderly nursing home residents

Selection bias is of critical concern in the study of influenza vaccine effectiveness when using an observational study design. This bias is attributable to the inherently different characteristics between vaccinees and non-vaccinees. The differences, which are related both to vaccination and signs of clinical disease as an outcome, may lead to erroneous estimation of the effectiveness. In this report, we describe how selection bias among elderly nursing home residents may lead to a spurious interpretation of the protective effect of influenza vaccine. Our results should be a lesson in the importance of regarding selection bias when assessing influenza vaccine effectiveness.

Guillain-Barré Syndrome and Preceding Infection with Campylobacter, Influenza and Epstein-Barr Virus in the General Practice Research Database

BackgroundA number of infectious agents have previously been suggested as risk factors for the development of Guillain-Barré syndrome (GBS), but robust epidemiologic evidence for these associations is lacking.Methods and FindingsWe conducted a nested case-control study using data from the United Kingdom General Practice Research Database between 1991 and 2001. Controls were matched to cases on general practice clinic, sex, year of birth and date of outcome diagnosis in their matched case. We found positive associations between GBS and infection with Campylobacter, Epstein-Barr virus and influenza-like illness in the previous two months, as well as evidence of a protective effect of influenza vaccination. After correction for under-ascertainment of Campylobacter infection, the excess risk of GBS following Campylobacter enteritis was 60-fold and 20% of GBS cases were attributable to this pathogen.ConclusionsOur findings indicate a far greater excess risk of GBS among Campylobacter enteritis patients than previously reported by retrospective serological studies. In addition, they confirm previously suggested associations between infection due to Epstein-Barr virus infection and influenza-like illness and GBS. Finally, we report evidence of a protective effect of influenza vaccination on GBS risk, which may be mediated through protection against influenza disease, or result from a lower likelihood of vaccination among those with recent infection. Cohort studies of GBS incidence in this population would help to clarify the burden of GBS due to influenza, and any potential protective effect of influenza vaccination.

In a prospective observational study, influenza vaccination prevented hospitalization among older home care patients

Objective The aim of the study is (1) to describe the prevalence of vaccination against influenza in older home care patients and (2) to investigate the protective effect of influenza vaccination for hospitalization events. Study Design and Setting This is an observational study conducted in four large cohorts of elderly patients in home care during the 1998–1999, 1999–2000, 2000–2001, and 2001–2002 influenza seasons. We analyzed data from the Italian Silver Network Home Care project. A total of 2,201 patients were enrolled in the present study. The main outcome measures were prevalence of vaccination against influenza and the rate of hospitalization according to vaccination status and influenza season. Results The rate of influenza vaccination was around 48% of the studied sample. During the follow-up including the peak of influenza and the total influenza season, 412 subjects (40%) were hospitalized among vaccinated compared to 610 subjects (59%) among not vaccinated ( P < 0.001). After adjusting for age, gender, location of home care program, and all the variables significantly different between vaccinated and not-vaccinated subjects, vaccinated subjects were less likely to be hospitalized compared to not-vaccinated subjects (OR, 0.73; 95% CI 0.60–0.90). Conclusions Vaccination against influenza has an important prognostic implication for frail geriatric patients living in the community.

Comparison of two vaccination programmes in preventing influenza-related hospitalization among the elderly during two consecutive seasons

The protective effect of influenza vaccine against influenza related hospitalization is well established at an individual level, but the effect of vaccination programme at the population level is unknown. In this study we compared a risk disease-based free-of-charge influenza vaccination programme in preventing hospitalizations due to influenza or pneumonia and cardiovascular diseases during 2 consecutive influenza seasons 1992/93 and 1993/94 in 43 municipalities in northern Finland. Vaccinations were carried out and reported by local staff in health centres. Data of hospital treatment periods were obtained from the National Hospital Discharge Register. During the influenza seasons the number of hospitalizations due to cardiovascular diseases and influenza/pneumonia increased by 13%. In the 1993/1994 season the increase in the study area with the risk disease-based vaccination programme was 22 per 1000 persons (95% CI 19-24), and with an age-based programme 3.3 per 1000 persons (95% CI 2.5-4.0), while the increase in the 1992/1993 season in both areas was 3-4 per 1000. The excess of hospitalization related to influenza epidemics is mostly due to cardiovascular diseases and varies from y to y, as do the benefits gained by vaccination.

Assessing influenza-related mortality: Comment on Zucs et al.

Assessing influenza-related mortality: Comment on Zucs et al.

Is influenza vaccination in asthma helpful?

Influenza infections are frequently involved in asthma exacerbations. During influenza epidemics substantial excess morbidity due to respiratory tract complications is reported in all age categories as well as excess mortality among the elderly. Vaccines are available for protection against influenza. Worldwide, vaccination is advised and considered a quality point for asthma care. However, the protective effect of influenza vaccination in patients with asthma is still disputed. In order to establish the current state of affairs we reviewed the recent literature on the protective effect of influenza vaccination and its usefulness in patients with asthma. Several studies were found addressing influenza and the protective aspects of vaccination. They discussed the incidence, the adverse effects of vaccination, the coverage of influenza vaccination among patients with asthma and the effectiveness of the vaccine. Influenza vaccination can safely be used in patients with asthma. Allegations that vaccination could provoke asthma exacerbations are convincingly invalidated by previous and recent research. Although patients with asthma are one of the major target groups for immunization, vaccine coverage in all age categories remains low. So far, no unequivocal beneficial effect of influenza vaccination in patients with asthma was found in observational and experimental studies in the sense of reduction of asthma exacerbations and other complications. Recent studies confirm these negative findings. More long-term randomized, placebo-controlled studies, focusing on influenza- proven illness in patients with asthma, are needed to address the question of how helpful influenza vaccination is in these patients.

Influenza Vaccination in Patients with Asthma: Effect on the Frequency of Upper Respiratory Tract Infections and Exacerbations

Influenza epidemics of variable extent and severity occur every winter and are frequently associated with exacerbations of asthma. Accordingly, annual vaccination against influenza is recommended for patients with asthma However, there are very limited data concerning its protective effect in this group of patients. The aim of this study was to assess the effect of influenza vaccination on the frequency of upper respiratory tract infections and also asthma‐related outcomes such as exacerbation rates, hospital admissions, and rescue courses of oral corticosteroids in patients with stable asthma. Between September 15 and November 7, 2001, a total of 128 patients with asthma were randomly assigned to receive (n = 86) and not to receive vaccine (n = 42). The primary outcome measures were frequency of upper respiratory tract infections and exacerbations of asthma during the winter following vaccination. Study subjects were asked to record the presence and duration of symptoms suggestive of an upper respiratory tract infection and call their physician in the presence of conditions suggestive of an exacerbation until March 2002. Among the vaccinated group, 48% of the patients reported that they had no upper respiratory tract infection during the winter following injection, whereas 57% of nonvaccinated participants were upper respiratory symptom free during the same period (p > 0.05). The frequency of upper respiratory tract infection was also not different between the two groups in all severity forms of asthma (p > 0.05). There was no significant difference in the frequency of exacerbations of asthma between the two groups during the study period (p > 0.05). None of the vaccinated group was hospitalized due to an asthma attack; however, two patients (4.8%) in the nonvaccinated group had to be hospitalized following an exacerbation (p > 0.05). In summary, our findings do not support the protective effect of influenza vaccination for patients with asthma. However, no firm conclusions on this effect of the vaccine can be made without the data on the rate of influenza epidemic in that season and without the knowledge of the cause of upper respiratory tract infections in those patients. Therefore, we believe randomized, double‐blind, placebo‐controlled studies, including larger subgroups of severe asthmatics, are needed to evaluate the protective effect of influenza vaccination in asthma.

A large outbreak of influenza A and B on a cruise ship causing widespread morbidity.

In September 2000 an outbreak of influenza-like illness was reported on a cruise ship sailing between Sydney and Noumea with over 1,100 passengers and 400 crew on board. Laboratory testing of passengers and crew indicated that both influenza A and B had been circulating on the ship. The cruise coincided with the peak influenza period in Sydney. Morbidity was high with 40 passengers hospitalized, two of whom died. A questionnaire was sent to passengers 3 weeks after the cruise and 836 of 1,119 (75%) responded. A total of 310 passengers (37%) reported suffering from an influenza-like illness (defined as cough, fever, myalgia and weakness) and 528 (63%) had seen a doctor for illness related to the cruise. One-third of passengers reported receipt of influenza vaccination in 2000; however neither their rates of influenza-like illness nor hospitalization were significantly different from those in unvaccinated passengers. A case-control study also found no significant protective effect of influenza vaccination. With the increasing popularity of cruise vacations, such outbreaks are likely to affect increasing numbers of people. Whilst influenza vaccination of passengers and crew may afford some protection, uptake and effectiveness may not be sufficient to prevent outbreaks. Surveillance systems and early intervention measures, such as antiviral therapies, should be considered to detect and control such outbreaks.

Vaccines for preventing influenza in people with asthma (Cochrane Review).

Influenza vaccination is recommended for asthmatic patients in many countries as observational studies have shown that influenza infection can be associated with asthma exacerbations, but influenza vaccination itself has the potential to adversely affect pulmonary function. A recent overview concluded that there was no clear benefit of influenza vaccination in patients with asthma but this conclusions was not based on a systematic search of the literature. Whilst influenza may cause asthma exacerbations, there is controversy about the use of influenza vaccinations, since they may precipitate an asthma attack in some people. The objective of this review was to assess the effects of influenza vaccination in children and adults with asthma. We searched the Cochrane Airways Group trials register and checked reference lists of articles. Randomised trials of influenza vaccination in children (over two years of age) and adults with asthma. Studies involving people with chronic obstructive pulmonary disease were excluded. Inclusion criteria and assessment of trial quality were applied by two reviewers independently. Data extraction was done by two reviewers independently. Study authors were contacted for missing information. Nine trials were included. Four of these trials were of high quality. One further article has been included since the previous version of this review. Inclusion of the new trial has not altered the conclusions of this review. The included studies covered a wide diversity of people, settings and types of influenza vaccination, so data from the different trials were not pooled. In one trial, no protective effect of influenza vaccination against asthma exacerbation was demonstrated, but the incidence of influenza was low during the study period. A higher number of asthma exacerbations following killed influenza vaccination was found in one trial (risk difference 3 1%, 95% confidence interval 0.3% to 5.8%). When people with upper respiratory tract infections were excluded, this difference was no longer significant. A small trial using recombinant vaccine found no significant difference in asthma exacerbations between the vaccinated and placebo groups. Updated search conducted July, 2000. No new trials were identified. There is not enough evidence to assess the benefits and risks of influenza vaccination for people with asthma.

Effect of influenza virus vaccination in infants and children, with antibody studies

Summary 1. From October, 1946, to March, 1947, 100 children ranging in ages from one month to 18 years were inoculated with influenza virus type A and B vaccine adsorbed on calcium phosphate. The dosages given to the different age groups have been outlined. 2. Reactions were mild and consisted of slight local soreness for twenty-fourhours in the majority of cases. Four children had a slight febrile reaction (100° to 100.6° F.), and one child had an elevation of temperature to 102.° F. Nodules following injection appeared in eight cases and persisted for a short time only. 3. Of the 100 children inculated, complete serologic data including pre-andpostvaccination antibody titers were obtained in forty children. 4. Of these forty children, twenty-two received a second injection of thevaccine, at intervals from two weeks to three months. Complete serologic data was obtained in five children following the second inoculation. There were no systemic reactions to the second injection of the vaccine. In our study there were no cases of induced sensitivity to the calcium phosphate-adsorbed vaccine in those children who received more than one injection. 5. Two hundred children of similar ages as the vaccinated children servedas controls. In the injected children there were three cases of influenza, an attack rate of 3 per cent and in the controls there were nineteen cases, an attack rate of 9.5 per cent. 6. There was a significant response to vaccination in children over 2 yearsof age, as judged by antibody levels, for serologic evidence indicated that the injected children had a rise in titer from seven to twenty-three times. 7. Although the average antibody response to injection in children over 2years of age was, on the whole, very satisfactory, and comparable to adults, there was an unevenness of this response as some children did not produce antibody against the PR8 strain and others failed to produce a satisfactory increase in antibody against the Lee strain. 8. It is probably significant that children below 2 years of age did not respond to the vaccine with good antibody production. 9. It was observed that the second inoculation did not produce a further sharp rise in circulating antibody in children over 2 years of age. 10. The results of our studies are in agreement with the data and observations of other investigators; namely, that subcutaneous vaccination with a vaccine containing inactivated influenza virus, types A and B, adsorbed on calcium phosphate is usually followed by a satisfactory rise in circulating antibody against these viruses in children over 2 years of age. 11. In view of the fact that a widespread epidemic of influenza anticipatedduring the fall and winter of 1946–1947 did not fully materialize, the number of cases of influenza was far below expectancy. Although our vaccinated group had a reduction in the attack rate, further studies are needed to prove conclusively the clinical efficacy of influenza vaccination in children, and no final conclusion regarding the protective effect of influenza vaccination in children can be drawn from this study.