Vaccination against influenza: a five-year study in the Post Office

On the use of hemagglutination-inhibition for influenza surveillance: surveillance data are predictive of influenza vaccine effectiveness

The hemagglutination-inhibition (HI) assay is the main tool used by epidemiologists to quantify antigenic differences between circulating influenza virus strains, with the goal of selecting suitable vaccine strains. However, such quantitative measures of antigenic difference were recently shown to have poor predictive accuracy with respect to influenza vaccine effectiveness (VE) in healthy adults. Here, we re-examine those results using a more rigorous criterion for predictive accuracy -- considering only cases when the vaccine (V) and dominant (D) circulating strains are antigenically different -- and greater numbers of HI titers. We find that the Archetti -- Horsfall measure of antigenic difference, which is based on both the normalized HI titer (NHI) of D relative to antisera raised against V and the NHI of V relative to D, predicts VE very well (R(2)=0.62, p=4.1x10(-3)). In contrast, the predictive accuracies of the NHI of D relative to V alone (R(2)=0.01), and two other measures of antigenic difference based on the amino acid sequence of influenza virus hemagglutinin (R(2)=0.03 for both measures) are relatively poor. Furthermore, while VE in the elderly is generally high in cases when D and V are antigenically identical (VE=35%, S.E.=5%), in other cases VE appears to increase with the antigenic difference between D and V (R(2)=0.90, p=2.5x10(-5)). This paradoxical observation could reflect the confounding effects of prior immunity on estimates of VE in the elderly. Together, our results underscore the need for consistently accurate selection of suitable vaccine strains. We suggest directions for further studies aimed at improving vaccine-strain selection and present a large collection of HI titers that will be useful to such studies.

Quantifying influenza vaccine efficacy and antigenic distance

We introduce a new measure of antigenic distance between influenza A vaccine and circulating strains. The measure correlates well with efficacies of the H3N2 influenza A component of the annual vaccine between 1971 and 2004, as do results of a theory of the immune response to influenza following vaccination. This new measure of antigenic distance is correlated with vaccine efficacy to a greater degree than are current state of the art phylogenetic sequence analyses or ferret antisera inhibition assays. We suggest that this new measure of antigenic distance be used in the design of the annual influenza vaccine and in the interpretation of vaccine efficacy monitoring.

A prospective, Internet-based study of the effectiveness and safety of influenza vaccination in the 2001–2002 influenza season

The effectiveness of the influenza vaccine used in the 2001-2002 influenza season in Japan was investigated in a large-scale, geographically widely distributed, Internet-based study. Data were collected from 8841 of 9902 subjects registered by 38 clinics prior to the start of influenza season. Subjects were categorized into three groups by vaccination regimen: unvaccinated, vaccinated once, and vaccinated twice. Efficacy was also analyzed for three age groups: 0-15, 16-64, and 65-104 years. Influenza-like illness (ILI) was diagnosed according to Ministry of Health (MWH, Labor and Welfare in Japan) criteria. Laboratory-confirmed influenza cases were analyzed separately. The respective vaccine efficacy in the 0-15 years group for the one- and two-dose regimens was 67.6 and 84.5% for ILI and 54.0 and 79.8% for laboratory-confirmed influenza. Influenza vaccination was also shown to be effective in subjects 16-64 years. Vaccine effectiveness was not able to be determined for the over 65 years group, probably due to an insufficient number of infected patients. These results suggest that influenza vaccination is effective for children and adults and that a two-dose regimen is superior to a single dose in children 0-15 years.

Pharmacoeconomics of influenza vaccination for healthy working adults: reviewing the available evidence

A favourable pharmacoeconomic profile has been well established for influenza vaccination in the elderly. For employers relevant benefits seem to exist for vaccinating healthy working adults to avert absenteeism and related production losses. From a pharmacoeconomic point of view it is relevant to consider whether societal benefits of vaccination for healthy working adults is worthwhile given the costs of vaccination for the community. We searched Medline and Embase using the key words influenza (vaccination) in combination with cost, cost-benefit, cost-effectiveness, efficiency, economic evaluation, health-policy and pharmacoeconomics. From this primary search, we selected 11 studies concerned with the group of healthy working adults. We reviewed these studies according to several criteria: benefit-to-cost (B/C) ratio;vaccine effectiveness, influenza incidence, number of days of work absence due to illness; and relative cost of the vaccine. Three studies on vaccinating healthy working adults found costs exceeding the benefits (B/C-ratio <1). The remaining eight pharmacoeconomic studies found a B/C-ratio of almost two or more. Cost savings are strongly related to the inclusion of indirect benefits related to averted production losses. After exclusion of indirect costs and benefits of production gains/losses, only one of the eight studies remains cost saving. Considering the available pharmacoeconomic evidence, vaccination of healthy working adults in Western countries may be an intervention with favourable cost-effectiveness and cost-saving potentials if indirect benefits of averted production losses are included. Excluding indirect benefits and costs of production losses/gains, cost-saving potentials are limited. Recent international guidelines for pharmacoeconomic research advise the inclusion of production gains and losses in the preferred societal perspective. Hence, on the basis of the available evidence, influenza vaccination of healthy working adults may be recommended from pharmacoeconomic point of view. Pharmacoeconomics do, however, present only one argument for consideration aside from ethical issues, budgetary limits and psychosocial aspects.

Pharmacoeconomics of influenza vaccination in the elderly: reviewing the available evidence

Most western countries have influenza vaccination programmes for citizens aged > or = 65 years. This paper reviews the available evidence on whether elderly influenza vaccination is worthwhile from a pharmacoeconomic point of view. A search on Medline and EMBASE resulted in a primary selection of approximately 100 studies on the pharmacoeconomics of influenza vaccination in the elderly. Further selection of studies to be included in the review was based on several criteria such as original research paper, cost-benefit or cost-effectiveness analysis. influenza vaccination in the elderly, and publication between 1980 and 1999. The 10 studies included in the final selection were evaluated regarding 3 main aspects: benefit-cost ratio and cost-effectiveness ratio; vaccine effectiveness; and relative costing of the vaccine. In general, differences in benefit-cost ratios could be explained by differences in effectiveness and relative costing of the vaccine. Considering the available pharmacoeconomic evidence, influenza vaccination of the elderly in western countries is an intervention with favourable cost-effectiveness in terms of net costs per life-year gained and even has cost-saving potential. In particular, influenza vaccination among elderly people at higher risk, such as the chronically ill elderly, is generally found to be cost saving. Relatively favourable cost-effectiveness among non-high-risk elderly justifies universal influenza vaccination of the elderly from a pharmacoeconomic point of view.

Randomized, placebo-controlled double blind study on the efficacy of influenza immunization on absenteeism of health care workers

BACKGROUND

In healthy adults influenza immunization reduces absenteeism caused by respiratory infections, but data on its efficacy among health care workers are scarce.

OBJECTIVE

To determine the effect of the conventional inactivated influenza A vaccine on reducing absenteeism related to respiratory infections among pediatric health care providers.

STUDY DESIGN

A randomized, placebo-controlled, double blind study on vaccine efficacy was conducted in two pediatric hospitals during the winter season 1996 to 1997. The primary endpoint was days of work lost from the hospital because of respiratory infections. The documentation of absenteeism was based on personal sickness logs.

RESULTS

Of the 547 randomized vaccinees 427 (78%) persons completed the 4-month follow-up and returned the sickness logs. Immunization failed to reduce episodes of respiratory infections (1.8 episodes/study period among vaccinees vs. 2.0 among controls). Similarly the vaccine failed to affect the total number of days the vaccinees suffered from respiratory infections (13.5 days vs. 14.6 days, respectively). However, days of work lost because of respiratory infections (1.0 days vs. 1.4 days, respectively, P = 0.02) and especially total numbers of days the study persons felt themselves unable to work when either on or off duty (2.5 days vs. 3.5 days, P 0.02) were significantly decreased.

CONCLUSION

Influenza vaccination reduced absenteeism related to respiratory infections by 28%. We therefore believe that routine annual influenza immunizations should be recommended to health care providers working in pediatric settings.

Cost-effectiveness of the influenza vaccine in a healthy, working-age population

To determine if the influenza vaccine can reduce absenteeism and the cost of Influenza-Like Illness (ILI) in healthy adults in the workplace, a prospective, non-randomized, non-placebo control trial was done in six North Carolina textile plants. One hundred thirty-one vaccinated employees were compared with 131 age- and gender-matched non-vaccines from different plants. Twenty-six (20%) of the vaccinated and 64 (49%) of the unvaccinated group had ILI (P = 0.0000008). Fifteen (11%) of the vaccinated and 31 (24%) of the unvaccinated employees missed work because of ILI (P = 0.01). There were 43 lost workdays in vaccinated and 93 in unvaccinated employees (P = 0.00004). The "cost per saved lost workday" was $22.36, for a company savings of $2.58 per dollar invested in the vaccination program. We concluded that the influenza vaccine can give significant reductions in incidence, absenteeism, and cost associated with ILJ in the workplace.

Influenza vaccination among healthy employees: a cost-benefit analysis

The cost of influenza vaccination and influenza infections was evaluated in a controlled study among healthy municipal homemakers. Acute respiratory infections were followed clinically and with laboratory samples for 8 months. Full follow-up was achieved in 351 persons in the intervention group, of whom 47% obtained vaccination, and 492 controls. Influenza infection was confirmed in 10 employees (8 of these in the control group) and other viral infections in 6 employees (5 of them controls). All infections occurred in non-vaccinated persons. The relative risk of infection in the control group was 2.9 (95% CI 0.6-13.4) for influenza and 3.1 (0.9-10.8) for all respiratory infections. The mean sick leave for influenza was 4.9 days. The cost per immunization was FIM 141, and the average cost per influenza infection FIM 1183. The cost per infection averted was FIM 6270, and the equivalent cost for immunization FIM 26.52. Influenza vaccination had a slight protective effect against both influenza and other respiratory infections. The cost of vaccination programmes exceeded the benefit from averted infections. Optimal vaccination strategies for healthy adults need to be planned individually with minimal loss of working time.

Economic evaluation of influenza vaccination and economic modelling. Can results be pooled?

Scientific reviewing methods were applied to economic studies of influenza vaccination, and an economic model of influenza vaccination was developed from these primary sources. Issues arising from the secondary literature review include the quality of evidence on the effectiveness of the vaccines, the absence of a traditional population-based approach to reviewing economic data, confusion in terminology, and how to generalise from resource data contained in primary evaluations. Data from the literature review were summarised in terms of resource units used in the prevention and treatment of influenza. An economic model was constructed using local unit costs (from the Emilia region of Italy) and applying the data to a notional population. The model was sensitive to length of stay in hospital but not to variation in incidence of influenza, days off work or number of medical consultations. The model was predicated on and is sensitive to an estimate of 80% vaccine effectiveness. The approach is constrained by the available data, but could be more generally useful in that it allows variations in the quantity of inputs to be considered separately from variations in their values. The model may be used locally as a decision-making tool, although the method needs further development.

The effectiveness of vaccination against influenza in healthy, working adults

BACKGROUND

Although influenza causes substantial morbidity and mortality in all age groups, current recommendations emphasize annual immunization for people at high risk for complications of influenza. We conducted a double-blind, placebo-controlled trial of vaccination against influenza in healthy, working adults.

METHODS

In the fall of 1994, we recruited working adults from 18 to 64 years of age from in and around the Minneapolis-St. Paul area and randomly assigned them to receive either influenza vaccine or placebo injections. The primary study outcomes included upper respiratory illnesses, absenteeism from work because of upper respiratory illnesses, and visits to physicians' offices for upper respiratory illnesses. The economic benefits of vaccination were analyzed by estimating the direct and indirect costs associated with immunization and with upper respiratory illnesses.

RESULTS

We enrolled a total of 849 subjects. Baseline characteristics were similar in the two groups. During the follow-up period, consisting of the 1994-1995 influenza season (December 1, 1994, through March 31, 1995), those who received the vaccine reported 25 percent fewer episodes of upper respiratory illness than those who received the placebo (105 vs. 140 episodes per 100 subjects, P < 0.001), 43 percent fewer days of sick leave from work due to upper respiratory illness (70 vs. 122 days per 100 subjects, P = 0.001), and 44 percent fewer visits to physicians' offices for upper respiratory illnesses (31 vs. 55 visits per 100 subjects, P = 0.004). The cost savings were estimated to be $46.85 per person vaccinated.

CONCLUSIONS

Vaccination against influenza has substantial health-related and economic benefits for healthy, working adults.

Influenza immunization in children with cystic fibrosis

Nineteen children with cystic fibrosis and aged between 5 and 13 years were randomized to receive two doses at monthly intervals of either a split-virion influenza vaccine (MFV-Ject, Institut Merieux) or a sub-unit vaccine (Fluvirin, Evans). In those completing the study, there was a satisfactory serological response. There was no statistically significant difference between the immunogenicity of the two vaccines as evaluated by haemagglutination inhibition or single radial haemolysis tests. The incidence of local side-effects was similar in the two groups.

[Inactivated vaccine against trivalent influenza. Comparative study of the immune response by hemagglutination inhibition and simple radial hemolysis methods]

A vacina inativada contra gripe, trivalente, preparada no Instituto Butantan, contendo 200 unidades hemaglutinantes de cada uma das cepas de virus Influenza A/SP/1/80 (H3N2), A/SP/1/78 (H1N1) e B/England/847/73, foi administrada em 110 voluntários humanos adultos, sendo que 62 receberam uma dose de vacina e 48 duas doses, com intervalo de 21 dias. A resposta de anticorpos específicos para influenza foi analisada comparativamente pelos testes de Inibição da Hemaglutinação (IH) e Hemólise Radial Simples (HRS). Ocorreu aumento significativo do teor de anticorpos nos indivíduos vacinados, correspondente a um aumento de 4 vezes ou mais nos títulos obtidos pelo teste IH e a um aumento de 3,0 mm ou maior no diâmetro das zonas de hemólise pelo teste HRS. Os métodos demonstraram correlação satisfatória entre si.

A comparison of adverse effects of two influenza vaccines, and the influence on subsequent uptake

In a study comparing the side effects of two influenza vaccines in a health centre vaccination programme involving patients in ;at risk' groups, no significant difference was found between the vaccines used or the method of administration. The majority of side effects were minor, but as many as 35 per cent of the study group reported some systemic upset after vaccination. A follow-up study a year later showed that the incidence of side effects did not appear to influence the uptake of revaccination.

The economics of prevention

A review of cost-effectiveness studies of prevention supports two conclusions: (1) few prevention programs, if any, reduce medical expenditures; (2) even when prevention costs less per person than acute care, its medical costs per unit of health benefit can be as great or greater. So that future studies will allow comparisons over a wider range of medical choices, the paper proposes some steps toward the greater standardization of cost-effectiveness analyses of medical care.

Dose response of A/Alaska/6/77 (H3N2) cold-adapted reassortant vaccine virus in adult volunteers: role of local antibody in resistance to infection with vaccine virus

An attenuated influenza A candidate vaccine virus, derived from the A/Ann Arbor/6/60 (H2N2) cold-adapted (ca) donor virus and the A/Alaska/6/77 (H3N2) wild-type virus, was evaluated in adult seronegative volunteers (serum hemagglutination-inhibiting antibody titer, less than or equal to 1:8) for level of attenuation, infectivity, antigenicity, and genetic stability. Four groups with similar preinoculation mean titers of serum and nasal wash antibodies were inoculated intranasally with 10(4.5), 10(5.5), 10(6.5), or 10(7.5) 50% tissue culture infectious doses (TCID50) of the ca reassortant virus, and eight other seronegative adult volunteers received the wild-type virus. Only 2 of 66 vaccinees developed fever or mild and brief systemic or upper respiratory tract illness or both. Both volunteers with vaccine-related reactions received the highest dose (10(7.5) TCID50) of ca virus, which indicates that the vaccine retains some mild reactogenicity at a high dosage. In contrast, four of eight volunteers infected with the wild-type virus became ill. Each of the 54 isolates tested retained the temperature-sensitive phenotype of the vaccine virus. Thus, the ca reassortant was genetically stable and attenuated at 10(4.5) to 10(7.5) TCID50 for seronegative adults. The 50% human infective dose of ca virus was approximately 10(5.3) TCID50. Ten and one hundred 50% human infectious doses infected 73 and 83% of vaccinees, respectively, and approximately 75% developed an immunological response at these doses. The failure of the vaccine virus to infect some volunteers was correlated with the presence of pre-inoculation nasal wash immunoglobulin A hemagglutinin antibody.

Humoral and cellular responses of mice to infection with a cold-adapted influenza A virus variant

The serum antibody response and four different cellular immune responses (cytotoxic T cells, delayed-type hypersensitivity T cells, natural killer cells, and cytotoxic macrophage levels) induced in CBA/H mice were measured at different times after intranasal inoculation of a cold-adapted (ca) variant of influenza A virus, influenza virus A/Ann Arbor/6/60-ca, or the parental virus, influenza virus A/Ann Arbor/6/60. At the highest dose of virus inoculated (5 log10 50% tissue culture infective doses), all four cellular responses reached high levels in the lungs of both groups of mice, and serum antibody titers were detected on day 20 after inoculation of either virus. However, whereas extensive replication of the parental virus occurred in the mouse lungs, very limited replication of the ca variant was observed. Macroscopically, infection with the parental virus caused gross lung damage, whereas such damage was almost absent in mice inoculated with the ca variant. Inoculation of 2 to 5 log10 50% tissue culture infective doses of the parental virus induced high cytotoxic T-cell responses, whereas only the highest dose of the ca variant caused a clearly significant cytotoxic T-cell response. As an inoculum of 5 log10 50% tissue culture infective doses of the ca variant caused a substantial primary immune response without appreciable lung damage, the avirulence of the ca variant may be primarily related to its limited ability to replicate productively in mouse lungs.