A review of attenuation of influenza viruses by genetic manipulation

Influenza viral neuraminidase: the forgotten antigen

Influenza is the most common cause of vaccine-preventable morbidity and mortality despite the availability of the conventional trivalent inactivated vaccine and the live-attenuated influenza vaccine. These vaccines induce an immunity dominated by the response to hemagglutinin (HA) and are most effective when there is sufficient antigenic relatedness between the vaccine strain and the HA of the circulating wild-type virus. Vaccine strategies against influenza may benefit from inclusion of other viral antigens in addition to HA. Epidemiologic evidence and studies in animals and humans indicate that anti-neuraminidase (NA) immunity will provide protection against severe illness or death in the event of a significant antigenic change in the HA component of the vaccine. However, there is little NA immunity induced by trivalent inactivated vaccine and live-attenuated influenza vaccine. The quantity of NA in influenza vaccines is not standardized and varies significantly among manufacturers, production lots and tested strains. The activity and stability of the NA enzyme is influenced by concentration of divalent cations. If immunity against NA is desirable, a better understanding of how the enzymatic properties affect the immunogenicity is needed.

Influenza: a unique problem in vaccination

The genetic attributes of the influenza virus lead to unique problems in vaccination. First, a highly mutable RNA genome, resulting in sequential antigenic variation, could potentially manifest as a vaccine failure or epidemic influenza. Second, a segmented genome that engenders the virus with the capacity for genetic reassortment and the introduction of new antigens into a host population could possibly result in a pandemic. The core problem in combating influenza is the need for continual vaccine revision and induction of broader heterovariant immunity. Current vaccines – the conventional inactivated vaccine and the live attenuated vaccine – rely on technology of strain selection and production methods that is decades old. The immunity induced by these vaccines is dominated by the response to hemagglutinin (HA) and, therefore, the vaccines are most effective when there is sufficient antigenic relatedness between the vaccine strain HA and the circulating wild-type virus HA. Consequently, these vaccines are susceptible to failure when an antigenically distinct virus emerges after the selection of the vaccine candidate strain. New vaccine strategies need to include immunization with other viral antigens in addition to HA, thereby broadening the immune response against influenza. Inclusion of the more slowly evolving neuraminidase and/or M2e in a vaccine against influenza could reduce the vulnerability to antigenic changes, and conserved antigens from internal proteins – nucleoprotein and M1 – delivered to induce T-cell helper and cytotoxic T cells, could ensure the presence of activated T cells that facilitate clearance of pandemic strains. Alternative production technologies, such as recombinant baculovirus and yeast, and different delivery methods, such as virus-like particles, should be explored to decrease vaccine production times and reduce reliance on embryonated eggs.

Immunization against influenza A virus: Comparison of conventional inactivated, live-attenuated and recombinant baculovirus produced purified hemagglutinin and neuraminidase vaccines in a murine model system

To simulate the 2003-2004 influenza season and compare available vaccination methods, immunologically naive mice were immunized with: influenza A virus hemagglutinin (rHA) and neuraminidase (rNA) from A/Panama/2007/99 H3N2 or A/Fujian/411/2002 H3N2 expressed by recombinant baculovirus, chromatographically purified, either as single antigens (rHA or rNA) or in combination (rHArNA); conventional inactivated monovalent (CIV) vaccines from each heterotypic strain; or a live-attenuated influenza (LAV) vaccine derived from the A/Panama/2007/99 strain. HA containing vaccines were highly immunogenic for the HA antigen, with no statistically significant differences among groups in the amount of homotypic anti-HA antibody induced. Little cross-reactive anti-HA antibody was induced by any vaccine, including LAV. Statistically, the greatest amount of anti-NA antibody was induced by the purified NA alone or in combination with purified HA; the least amount of anti-NA antibody was found in mice immunized with LAV or CIV. Immunization with vaccines immunogenic for both HA and NA resulted in an immune response to both surface glycoproteins that suppressed homotypic, closely related heterotypic infection and had a greater reduction in mPVT following an infectious challenge by a distantly related heterotypic strain. These studies suggest that vaccines immunogenic for both HA and NA offer an increased level of protection from influenza.

Recommendations for influenza immunization of children

Epidemiologic studies indicate that children of all ages with certain chronic conditions and otherwise healthy children younger than 24 months of age are hospitalized for influenza infection and its complications at high rates similar to those experienced by the elderly. Annual influenza immunization is recommended for all children with high-risk conditions who are 6 months of age and older. Young, healthy children are at high risk of hospitalization for influenza infection; therefore, the American Academy of Pediatrics recommends influenza immunization for healthy children 6 through 24 months of age, for household contacts and out-of-home caregivers of all children younger than 24 months of age, and for health care professionals. To protect these children more fully against the complications of influenza, increased efforts are needed to identify all high-risk children and inform their parents when annual immunization is due. The purposes of this statement are to update recommendations for routine use of influenza vaccine in children and to review the indications for use of trivalent inactivated influenza vaccine and live-attenuated influenza vaccine.

Safety of cold-adapted live attenuated influenza vaccine in a large cohort of children and adolescents

OBJECTIVE

To determine the safety of cold-adapted trivalent intranasal influenza virus vaccine (CAIV) in children and adolescents.

STUDY DESIGN

A randomized, double blind, placebo-controlled safety trial in healthy children age 12 months to 17 years given CAIV (FluMist; MedImmune Vaccines, Inc.) or placebo (randomization, 2:1). Children <9 years of age received a second dose of CAIV or placebo 28 to 42 days after the first dose. Enrolled children were then followed for 42 days after each vaccination for all medically attended events. Prespecified outcomes included 4 prespecified diagnostic groups and 170 observed individual diagnostic categories. The relative risk and the 2-sided 90% confidence interval were calculated for each diagnostic group and individual category by clinical setting, dose and age. More than 1500 relative risk analyses were performed.

RESULTS

A total of 9689 evaluable children were enrolled in the study. Of the 4 prespecified diagnostic categories (acute respiratory tract events, systemic bacterial infection, acute gastrointestinal tract events and rare events potentially associated with wild-type influenza), none was associated with vaccine. Of the biologically plausible individual diagnostic categories, 3, acute gastrointestinal events, acute respiratory events and abdominal pain, had different analyses that demonstrated increased and decreased relative risks, making their association with the vaccine unlikely. For reactive airway disease a significant increased relative risk was observed in children 18 to 35 months of age with a relative risk of 4.06 (90% confidence interval, 1.29 to 17.86) in this age group. The individual diagnostic categories of upper respiratory infection, musculoskeletal pain, otitis media with effusion and adenitis/adenopathy had at least one analysis that achieved a significant increased risk ratio. All of these events were infrequent.

CONCLUSION

CAIV was generally safe in children and adolescents. The observation of an increased risk of asthma/reactive airway disease in children <36 months of age is of potential concern. Further studies are planned to evaluate the risk of asthma/reactive airway disease after vaccine.

Bronchodilator effect of an inhaled combination therapy with salmeterol + fluticasone and formoterol + budesonide in patients with COPD

In the present trial, we compared the broncholytic efficacy of the combination therapy with 50 microg salmeterol + 250 microg fluticasone and 12 microg formoterol + 400 microg budesonide, both in a single inhaler device, in 16 patients with moderate-to-severe COPD. The study was performed using a single-blind crossover randomized study. Lung function, pulse oximetry (SpO2) and heart rate were monitored before and 15, 30, 60, 120, 180, 240, 300, 360, 480, 600, and 720 min after bronchodilator inhalation. Both combinations were effective in reducing airflow obstruction. FEV1 AUC(0-12 h) was 2.83 l (95% CI: 2.13-3.54) after salmeterol/fluticasone and 2.57 l (95% CI: 1.97-3.2) after formoterol/budesonide. Formoterol/budesonide elicited the mean maximum improvement in FEV1 above baseline after 120 min (0.29 l; 95% CI: 0.21-0.37) and salmeterol/fluticasone after 300 min (0.32 l; 95% CI: 0.23-0.41). At 720 min, the increase in FEV1 over baseline values was 0.10 l (95% CI: 0.07-0.12) after salmeterol/fluticasone and 0.10 l (95% CI: 0.07-0.13) after formoterol/budesonide. The mean peak increase in heart rate occurred 300 min after formoterol/budesonide (1.5 b/min; 95% CI--2.3 to 5.3) and 360 min after salmeterol/fluticasone (2.6 b/min; 95% CI--1.9 to 7.0). SpO2 did not change. All differences between salmeterol/fluticasone and formoterol/budesonide were not significant (P > 0.05) except those in FEV1 at 120 and 360 min. The results indicate that an inhaled combination therapy with a long-acting beta2-agonist and an inhaled corticosteroid appears to be effective in improving airway limitation after acute administration in patients suffering from COPD.

Technical report: Reduction of the influenza burden in children

Epidemiologic studies have shown that children of all ages with certain chronic conditions, such as asthma, and otherwise healthy children younger than 24 months (6 through 23 months) are hospitalized for influenza and its complications at high rates similar to those experienced by the elderly. Annual influenza immunization is already recommended for all children 6 months and older with high-risk conditions. By contrast, influenza immunization has not been recommended for healthy young children. To protect children against the complications of influenza, increased efforts are needed to identify and recall high-risk children. In addition, immunization of children between 6 through 23 months of age and their close contacts is now encouraged to the extent feasible. Children younger than 6 months may be protected by immunization of their household contacts and out-of-home caregivers. The ultimate goal is universal immunization of children 6 to 24 months of age. Issues that need to be addressed before institution of routine immunization of healthy young children include education of physicians and parents about the morbidity caused by influenza, adequate vaccine supply, and appropriate reimbursement of practitioners for influenza immunization. This report contains a summary of the influenza virus, protective immunity, disease burden in children, diagnosis, vaccines, and antiviral agents.

Formoterol therapy for chronic obstructive pulmonary disease: a review of the literature

Numerous clinical trials have investigated the use of formoterol, a long-acting beta2-agonist, for the treatment of chronic obstructive pulmonary disease (COPD). Formoterol provides bronchodilation as rapidly as albuterol, yet its efficacy and duration of action are similar to those of salmeterol. It demonstrates better spirometric efficacy than either ipratropium or theophylline alone, and its efficacy improves when administered in combination with ipratropium. Formoterol improves patients' quality of life and has a good safety profile. It is better tolerated than theophylline and has a similar tolerability to albuterol, salmeterol, and ipratropium. In short, formoterol is a bronchodilator with rapid onset of action and prolonged duration of action with a favorable efficacy, safety, and tolerability profile when used in patients with COPD. It provides a valid therapeutic option in the pharmacologic treatment of this disease.

Live attenuated vaccines against influenza; an historical review

Live attenuated vaccines administered directly to the respiratory tract offer the promise of providing more effective immunity against influenza than subunit or split inactivated vaccines. Evidence has accumulated in recent years that immunological responses relevant to both the prevention of and recovery from influenza are best induced by natural infection. The ease with which the genes of influenza viruses reassort when two or more viruses infect a single cell has been exploited as a means of rapidly producing attenuated vaccines. Donor strains that have been shown by extensive testing to be fully attenuated are used to co-infect cells with contemporary epidemic strains to produce reassortants with the required degree of avirulence and the surface antigens of the epidemic strain. Reassortants prepared from cold-adapted mutants of both influenza A and B viruses have been widely shown from clinical trials in both the United States and Russia over many years to be well tolerated in both adults and children and to be highly efficacious.

Long-acting beta2 agonists in the management of stable chronic obstructive pulmonary disease

Long-acting beta2 agonist bronchodilators (e.g. formoterol, salmeterol) are a new interesting therapeutic option for patients with chronic obstructive pulmonary disease (COPD). In the short term, both salmeterol and formoterol appear to be more effective than short-acting beta2 agonists, and in patients with stable COPD they are more effective than anticholinergic agents and theophylline. Regular treatment of patients with COPD with long-acting beta2 agonists can induce an improvement in the respiratory function and certain aspects of quality of life. Moreover, salmeterol seems to be better than ipratropium and theophylline in improving lung function at the recommended doses after a long term treatment. Use of combination therapy of a long-acting inhaled beta2 agonist and an anticholinergic agent or theophylline in patients with COPD has not been sufficiently studied. Combination of usual doses of ipratropium or oxitropium with usual doses of salmeterol or formoterol does not appear to improve pulmonary function, but this lack of improvement with the combination should not, in itself, prevent implementation of further therapeutic steps in patients responsive to an anticholinergic agent and/or salmeterol or formoterol administered singly. Neither formoterol nor salmeterol elicit significant cardiovascular effects in healthy individuals and patients with reversible airway obstruction. However, adverse cardiac events might occur in patients with COPD with pre-existing cardiac arrhythmias and hypoxaemia if they use long-acting 12 agonists, although the recommended single dose of salmeterol 50 microg or formoterol 12 microg ensures a relatively higher safety margin than formoterol 24 microg. The bronchodilatory effect of long-acting beta2 agonists seems to be fairly stable after regular treatment with these bronchodilators. Moreover, pre-treatment with a conventional dose of formoterol or salmeterol does not preclude the possibility of inducing further bronchodilation with salbutamol in patients with partially reversible COPD. All these findings support the use of long-acting beta2 agonist bronchodilators as first-line bronchodilator therapy for the long term treatment of airflow obstruction in patients with COPD. However, since physicians must always choose a drug that is highly efficacious, well tolerated and inexpensive, the cost-effectiveness analysis in relation to other bronchodilators will determine the proper place of long-acting beta2 agonists in the long term therapy of stable COPD.

Promises and challenges of live-attenuated intranasal influenza vaccines across the age spectrum: a review

Despite the availability of inactivated influenza vaccines, influenza continues to cause considerable mortality in the elderly, and morbidity in all age groups. Cold-adapted, live-attenuated, intranasally administered influenza vaccines, first developed in the 1960s, have been tested in more than 10,000 volunteers and have been shown to be safe, well-tolerated, and immunogenic. Recent trials suggest that efficacy in children may be superior to that of inactivated vaccines, and efficacy in healthy adults may be similar to that of inactivated vaccines, although there are limited data comparing the two vaccines directly. Advantages of the live-attenuated vaccines include acceptability, ease of administration, and the potential for mass immunization. The possibility of substantially higher vaccination rates across all age groups brings promise for the development of herd immunity and greatly improved control of influenza in the future.

Efficacy of vaccination with live attenuated, cold-adapted, trivalent, intranasal influenza virus vaccine against a variant (A/Sydney) not contained in the vaccine

OBJECTIVE

To determine the safety, immunogenicity, and efficacy of revaccination of children with live attenuated influenza vaccine.

STUDY DESIGN

A 2-year multicenter, double-blind, placebo-controlled, efficacy field trial of live attenuated, cold-adapted trivalent influenza vaccine administered by nasal spray to children. This report summarizes year 2 results, a year in which the epidemic strain of influenza A/Sydney was not well matched to the vaccine strains. Each year, vaccine strains were antigenically equivalent to the contemporary inactivated influenza vaccine. In year 2, a single intranasal revaccination was administered. Active surveillance for influenza was conducted during the influenza season by means of viral cultures. Influenza cases were defined as illnesses with wild-type influenza virus isolated from respiratory secretions.

RESULTS

In year 2, 1358 (85%) children, 26 to 85 months of age, returned for revaccination. The intranasal vaccine was easily accepted, well tolerated, and immunogenic. Revaccination resulted in 82% to 100% of the vaccinated children in a subset studied for immunogenicity being seropositive as compared with 26% to 65% of placebo recipients, depending on the influenza strain tested. No serious adverse events were associated with the vaccine. In addition to the strains in the vaccine, antibody was induced to the variant strain A/Sydney/H3N2. In year 2, influenza A/Sydney/H3N2, a variant not contained in the vaccine, caused 66 of 70 cases of influenza A; nonetheless, intranasal vaccine was 86% efficacious in preventing A/Sydney influenza. Eight cases of lower respiratory tract disease were associated with A/Sydney influenza; all cases were in the placebo group.

CONCLUSIONS

This live attenuated, cold-adapted influenza vaccine was safe, immunogenic, and efficacious against influenza A/H3N2 (including a variant, A/Sydney, not contained in the vaccine) and influenza B. The characteristics of this vaccine make it suitable for routine use in children to prevent influenza.

Incremental benefit of adding oxitropium bromide to formoterol in patients with stable COPD

The effects of the long-acting beta(2)-agonist formoterol, the anticholinergic drug oxitropium bromide, and their combination were compared in 16 patients with partially reversible stable COPD. On each of 4 study days patients inhaled both drugs separated by 180 min in alternate sequence, with formoterol being administered in two doses (formoterol 12 microg + oxitropium bromide 200 microg; oxitropium bromide 200 microg + formoterol 12 microg; formoterol 24 microg + oxitropium bromide 200 microg; oxitropium bromide 200 microg + formoterol 24 microg). FEV(1)and FVC were measured baseline and after 30, 60, 120, 180, 210, 240, 300 and 360 min. In terms of onset of action, formoterol performed better than oxitropium bromide. Within the first 180 min after inhalation formoterol 24 microg was the most effective drug (maximal change in FEV(1): formoterol 24 microg = 25.6%, formoterol 12 microg = 21.1%, oxitropium bromide = 18.2%). Increased bronchodilation was obtained when the second drug was added, the sequence formoterol 24 microg + oxitropium bromide being the most effective (maximal change in FEV(1)over baseline: formoterol 24 microg + oxitropium bromide 28.8%, oxitropium bromide + formoterol 24 microg 20.9%, formoterol 12 microg + oxitropium bromide 26.6%, oxitropium bromide + formoterol 12 microg 22.5%). Significant improvement in pulmonary function may be achieved by giving two different bronchodilators in stable COPD patients. The sequence formoterol 24 microg + oxitropium bromide 200 microg seems to be the most effective.

The efficacy of live attenuated, cold-adapted, trivalent, intranasal influenzavirus vaccine in children

BACKGROUND

Influenzavirus vaccine is used infrequently in healthy children, even though the rates of influenza in this group are high. We conducted a multicenter, double-blind, placebo-controlled trial of a live attenuated, cold-adapted, trivalent influenzavirus vaccine in children 15 to 71 months old.

METHODS

Two hundred eighty-eight children were assigned to receive one dose of vaccine or placebo given by intranasal spray, and 1314 were assigned to receive two doses approximately 60 days apart. The strains included in the vaccine were antigenically equivalent to those in the inactivated influenzavirus vaccine in use at the time. The subjects were monitored with viral cultures for influenza during the subsequent influenza season. A case of influenza was defined as an illness associated with the isolation of wild-type influenzavirus from respiratory secretions.

RESULTS

The intranasal vaccine was accepted and well tolerated. Among children who were initially seronegative, antibody titers increased by a factor of four in 61 to 96 percent, depending on the influenza strain. Culture-positive influenza was significantly less common in the vaccine group (14 cases among 1070 subjects) than the placebo group (95 cases among 532 subjects). The vaccine efficacy was 93 percent (95 percent confidence interval, 88 to 96 percent) against culture-confirmed influenza. Both the one-dose regimen (89 percent efficacy) and the two-dose regimen (94 percent efficacy) were efficacious, and the vaccine was efficacious against both strains of influenza circulating in 1996-1997, A(H3N2) and B. The vaccinated children had significantly fewer febrile illnesses, including 30 percent fewer episodes of febrile otitis media (95 percent confidence interval, 18 to 45 percent; P<0.001).

CONCLUSIONS

A live attenuated, cold-adapted influenzavirus vaccine was safe, immunogenic, and effective against influenza A(H3N2) and B in healthy children.