Duration of Virus Shedding After Trivalent Intranasal Live Attenuated Influenza Vaccination in Adults

Performance evaluation of the Panbio COVID-19/Flu A&B Panel for detection of SARS-CoV-2, influenza A, and influenza B antigens using mid-turbinate nasal swabs

The Panbio COVID-19/Flu A&B Panel (Abbott) is an in vitro diagnostic rapid test designed for the qualitative detection of nucleocapsid proteins SARS-CoV-2 and nucleoprotein influenza A and B antigens in nasal mid-turbinate (NMT) swab specimens from symptomatic individuals meeting COVID-19 and influenza clinical and/or epidemiological criteria. This study, the largest global one to date using fresh samples, aimed to assess the diagnostic sensitivity and specificity of the Panbio COVID-19/Flu A&B Panel in freshly collected NMT swab specimens from individuals suspected of respiratory viral infection consistent with COVID-19 and/or influenza within the first 5 days of symptom onset compared with results obtained with the cobas SARS-CoV-2 and influenza A/B qualitative assay (cobas 6800/8800 systems), which were tested using nasopharyngeal swab samples. A total of 512 evaluable subjects were enrolled in the COVID-19 cohort across 18 sites, and 1,148 evaluable subjects were enrolled in the influenza cohort across 22 sites in the Asia-Pacific, Europe, and the USA. The Panbio COVID-19/Flu A&B Panel demonstrated a sensitivity of 80.4% and a specificity of 99.7% for COVID-19. For influenza A, the sensitivity and specificity rates were 80.6% and 99.3%, respectively. Likewise, for influenza B, the sensitivity and specificity rates were 80.8% and 99.4%, respectively. In conclusion, the Panbio COVID-19/Flu A&B Panel emerges as a suitable rapid test for detecting COVID-19 and influenza in symptomatic subjects across diverse global populations, exhibiting high sensitivity. The assay achieved a sensitivity of 94.4% in samples with Ct ≤24 for COVID-19 and 92.6% in samples with Ct ≤30 for influenza A and B.

IMPORTANCE

The Panbio COVID-19/Flu A&B Panel is a suitable rapid test for detecting COVID-19 and influenza in symptomatic subjects across diverse global populations, exhibiting high sensitivity. The assay achieved a sensitivity of 94.0% in samples with Ct ≤24 for COVID-19 and 92.6% in samples with Ct ≤30 for influenza A and B.

Next generation live-attenuated influenza vaccine platforms

INTRODUCTION

Influenza virus is a major cause of seasonal epidemics and intermittent pandemics. Despite the current molecular biology and vaccine development, influenza virus infection is a significant burden. Vaccines are considered an essential countermeasure for effective control and prevention of influenza virus infection. Even though current influenza virus vaccines provide efficient protection against seasonal influenza outbreaks, the efficacy of these vaccines is not suitable due to antigenic changes of the viruses.

AREAS COVERED

This review focuses on different live-attenuated platforms for influenza virus vaccine development and proposes essential considerations for a rational universal influenza virus vaccine design.

EXPERT OPINION

Despite the recent efforts for universal influenza virus vaccines, there is a lack of broadly reactive antibodies' induction that can confer broad and long-lasting protection. Various strategies using live-attenuated influenza virus vaccines (LAIVs) are investigated to induce broadly reactive, durable, and cross-protective immune responses. LAIVs based on NS segment truncation prevent influenza virus infection and have shown to be effective vaccine candidates among other vaccine platforms. Although many approaches have been used for LAIVs generation, there is still a need to focus on the LAIVs development platforms to generate a universal influenza virus vaccine candidate.

Pre-existing influenza-specific nasal IgA or nasal viral infection does not affect live attenuated influenza vaccine immunogenicity in children

The United Kingdom has a national immunization programme which includes annual influenza vaccination in school-aged children, using live attenuated influenza vaccine (LAIV). LAIV is given annually, and it is unclear whether repeat administration can affect immunogenicity. Because LAIV is delivered intranasally, pre-existing local antibody might be important. In this study, we analysed banked samples from a study performed during the 2017/18 influenza season to investigate the role of pre-existing influenza-specific nasal immunoglobulin (Ig)A in children aged 6-14 years. Nasopharyngeal swabs were collected prior to LAIV immunization to measure pre-existing IgA levels and test for concurrent upper respiratory tract viral infections (URTI). Oral fluid samples were taken at baseline and 21-28 days after LAIV to measure IgG as a surrogate of immunogenicity. Antibody levels at baseline were compared with a pre-existing data set of LAIV shedding from the same individuals, measured by reverse transcription-polymerase chain reaction. There was detectable nasal IgA specific to all four strains in the vaccine at baseline. However, baseline nasal IgA did not correlate with the fold change in IgG response to the vaccine. Baseline nasal IgA also did not have an impact upon whether vaccine virus RNA was detectable after immunization. There was no difference in fold change of antibody between individuals with and without an URTI at the time of immunization. Overall, we observed no effect of pre-existing influenza-specific nasal antibody levels on immunogenicity, supporting annual immunization with LAIV in children.

Pneumococcal colonization impairs mucosal immune responses to live attenuated influenza vaccine

Influenza virus infections affect millions of people annually, and current available vaccines provide varying rates of protection. However, the way in which the nasal microbiota, particularly established pneumococcal colonization, shape the response to influenza vaccination is not yet fully understood. In this study, we inoculated healthy adults with live Streptococcuspneumoniae and vaccinated them 3 days later with either tetravalent-inactivated influenza vaccine (TIV) or live attenuated influenza vaccine (LAIV). Vaccine-induced immune responses were assessed in nose, blood, and lung. Nasal pneumococcal colonization had no impact upon TIV-induced antibody responses to influenza, which manifested in all compartments. However, experimentally induced pneumococcal colonization dampened LAIV-mediated mucosal antibody responses, primarily IgA in the nose and IgG in the lung. Pulmonary influenza-specific cellular responses were more apparent in the LAIV group compared with either the TIV or an unvaccinated group. These results indicate that TIV and LAIV elicit differential immunity to adults and that LAIV immunogenicity is diminished by the nasal presence of S. pneumoniae. Therefore, nasopharyngeal pneumococcal colonization may affect LAIV efficacy.

Influenza A virus infection-induced macroautophagy facilitates MHC class II-restricted endogenous presentation of an immunodominant viral epitope

CD4⁺ T cells recognize peptides presented by major histocompatibility complex class II molecules (MHC-II). These peptides are generally derived from exogenous antigens. Macroautophagy has been reported to promote endogenous antigen presentation in viral infections. However, whether influenza A virus (IAV) infection-induced macroautophagy also leads to endogenous antigen presentation through MHC-II is still debated. In this study, we show that IAV infection leads to endogenous presentation of an immunodominant viral epitope NP_311-325 by MHC-II to CD4⁺ T cells. Mechanistically, such MHC-II-restricted endogenous IAV antigen presentation requires de novo protein synthesis as it is inhibited by the protein synthesis inhibitor cycloheximide, and a functional ER-Golgi network as it is totally blocked by Brefeldin A. These results indicate that MHC-II-restricted endogenous IAV antigen presentation is dependent on de novo antigen and/or MHC-II synthesis, and transportation through the ER-Golgi network. Furthermore, such endogenous IAV antigen presentation by MHC-II is enhanced by TAP deficiency, indicating some antigenic peptides are of cytosolic origin. Most importantly, the bulk of such MHC-II-restricted endogenous IAV antigen presentation is blocked by autophagy inhibitors (3-MA and E64d) and deletion of autophagy-related genes, such as Beclin1 and Atg7. We have further demonstrated that in dendritic cells, IAV infection prevents autophagosome-lysosome fusion and promotes autophagosome fusion with MHC class II compartment (MIIC), which likely promotes endogenous IAV antigen presentation by MHC-II. Our results provide strong evidence that IAV infection-induced autophagosome formation facilitates endogenous IAV antigen presentation by MHC-II to CD4⁺ T cells. The implication for influenza vaccine design is discussed.

Impact of influenza vaccine-modified infectivity on attack rate, case fatality ratio and mortality

Generally, vaccines are designed to provide protection against infection (susceptibility), disease (symptoms and transmissibility), and/or complications. In a recent study of influenza vaccination, it was observed that vaccinated yet infected individuals experienced increased transmission levels. In this paper, using a mathematical model of infection and transmission, we study the impact of vaccine-modified effects, including susceptibility and infectivity, on important epidemiological outcomes of an immunization program. The balance between vaccine-modified susceptibility, infectivity and recovery needed in preventing an influenza outbreak, or in mitigating the health outcomes of the outbreak is studied using the SIRV-type of disease transmission model. We also investigate the impact of influenza vaccination program on the infection risk of vaccinated and non-vaccinated individuals.

Novel Approaches for The Development of Live Attenuated Influenza Vaccines

Influenza virus still represents a considerable threat to global public health, despite the advances in the development and wide use of influenza vaccines. Vaccination with traditional inactivate influenza vaccines (IIV) or live-attenuated influenza vaccines (LAIV) remains the main strategy in the control of annual seasonal epidemics, but it does not offer protection against new influenza viruses with pandemic potential, those that have shifted. Moreover, the continual antigenic drift of seasonal circulating influenza viruses, causing an antigenic mismatch that requires yearly reformulation of seasonal influenza vaccines, seriously compromises vaccine efficacy. Therefore, the quick optimization of vaccine production for seasonal influenza and the development of new vaccine approaches for pandemic viruses is still a challenge for the prevention of influenza infections. Moreover, recent reports have questioned the effectiveness of the current LAIV because of limited protection, mainly against the influenza A virus (IAV) component of the vaccine. Although the reasons for the poor protection efficacy of the LAIV have not yet been elucidated, researchers are encouraged to develop new vaccination approaches that overcome the limitations that are associated with the current LAIV. The discovery and implementation of plasmid-based reverse genetics has been a key advance in the rapid generation of recombinant attenuated influenza viruses that can be used for the development of new and most effective LAIV. In this review, we provide an update regarding the progress that has been made during the last five years in the development of new LAIV and the innovative ways that are being explored as alternatives to the currently licensed LAIV. The safety, immunogenicity, and protection efficacy profile of these new LAIVs reveal their possible implementation in combating influenza infections. However, efforts by vaccine companies and government agencies will be needed for controlled testing and approving, respectively, these new vaccine methodologies for the control of influenza infections.

Influenza Virus Detection Following Administration of Live-Attenuated Intranasal Influenza Vaccine in Children With Cystic Fibrosis and Their Healthy Siblings

Background.  We aimed to explore the detection profile of influenza viruses following live-attenuated intranasal influenza vaccination (LAIV) in children aged 2-19 years with and without cystic fibrosis (CF). Methods.  Before the 2013-2014 influenza season, flocked nasal swabs were obtained before vaccination and 4 times in the week of follow-up from 76 participants (n_CF: 57; n_healthy: 19). Influenza was detected by reverse transcription polymerase chain reaction (RT-PCR) assays. A Bayesian hierarchical logistic regression model was used to estimate the effect of CF status and age on influenza detection. Results.  Overall, 69% of the study cohort shed influenza RNA during follow-up. The mean duration of RT-PCR detection was 2.09 days (95% credible interval [CrI]: 1.73-2.48). The odds of influenza RNA detection on day 1 following vaccination decreased with age in years (odds ratio [OR]: 0.82 per year; 95% CrI: 0.70-0.95), and subjects with CF had higher odds of influenza RNA detection on day 1 of follow-up (OR: 5.09; 95% CrI: 1.02-29.9). Conclusion.  Despite the small sample size, our results indicate that LAIV vaccine strains are detectable during the week after LAIV, mainly in younger individuals and vaccinees with CF. It remains unclear whether recommendations for avoiding contact with severely immunocompromised patients should differ for these groups.

Prevention and Control of Seasonal Influenza with Vaccines

This report updates the 2015-16 recommendations of the Advisory Committee on Immunization Practices (ACIP) regarding the use of seasonal influenza vaccines (Grohskopf LA, Sokolow LZ, Olsen SJ, Bresee JS, Broder KR, Karron RA. Prevention and control of influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices, United States, 2015-16 influenza season. MMWR Morb Mortal Wkly Rep 2015;64:818-25). Routine annual influenza vaccination is recommended for all persons aged ≥6 months who do not have contraindications. For the 2016-17 influenza season, inactivated influenza vaccines (IIVs) will be available in both trivalent (IIV3) and quadrivalent (IIV4) formulations. Recombinant influenza vaccine (RIV) will be available in a trivalent formulation (RIV3). In light of concerns regarding low effectiveness against influenza A(H1N1)pdm09 in the United States during the 2013-14 and 2015-16 seasons, for the 2016-17 season, ACIP makes the interim recommendation that live attenuated influenza vaccine (LAIV4) should not be used. Vaccine virus strains included in the 2016-17 U.S. trivalent influenza vaccines will be an A/California/7/2009 (H1N1)-like virus, an A/Hong Kong/4801/2014 (H3N2)-like virus, and a B/Brisbane/60/2008-like virus (Victoria lineage). Quadrivalent vaccines will include an additional influenza B virus strain, a B/Phuket/3073/2013-like virus (Yamagata lineage).Recommendations for use of different vaccine types and specific populations are discussed. A licensed, age-appropriate vaccine should be used. No preferential recommendation is made for one influenza vaccine product over another for persons for whom more than one licensed, recommended product is otherwise appropriate. This information is intended for vaccination providers, immunization program personnel, and public health personnel. Information in this report reflects discussions during public meetings of ACIP held on October 21, 2015; February 24, 2016; and June 22, 2016. These recommendations apply to all licensed influenza vaccines used within Food and Drug Administration-licensed indications, including those licensed after the publication date of this report. Updates and other information are available at CDC's influenza website (http://www.cdc.gov/flu). Vaccination and health care providers should check CDC's influenza website periodically for additional information.

Influenza Vaccination of Healthcare Workers and Vaccine Allocation for Healthcare Workers During Vaccine Shortages

Influenza causes substantial morbidity and mortality annually, particularly in high-risk groups such as the elderly, young children, immunosuppressed individuals, and individuals with chronic illnesses. Healthcare-associated transmission of influenza contributes to this burden but is often under-recognized except in the setting of large outbreaks. The Centers for Disease Control and Prevention has recommended annual influenza vaccination for healthcare workers (HCWs) with direct patient contact since 1984 and for all HCWs since 1993. The rationale for these recommendations is to reduce the chance that HCWs serve as vectors for healthcare-associated influenza due to their close contact with high-risk patients and to enhance both HCW and patient safety. Despite these recommendations as well as the effectiveness of interventions designed to increase HCW vaccination rates, the percentage of HCWs vaccinated annually remains unacceptably low. Ironically, at the same time that campaigns have sought to increase HCW vaccination rates, vaccine shortages, such as the shortage during the 2004-2005 influenza season, present challenges regarding allocation of available vaccine supplies to both patients and HCWs. This two-part document outlines the position of the Society for Healthcare Epidemiology of America on influenza vaccination for HCWs and provides guidance for the allocation of influenza vaccine to HCWs during a vaccine shortage based on influenza transmission routes and the essential need for a practical and adaptive strategy for allocation. These recommendations apply to all types of healthcare facilities, including acute care hospitals, long-term-care facilities, and ambulatory care settings.

Influenza Immunization for All Health Care Personnel: Keep It Mandatory

The purpose of this statement is to reaffirm the American Academy of Pediatrics' support for a mandatory influenza immunization policy for all health care personnel. With an increasing number of organizations requiring influenza vaccination, coverage among health care personnel has risen to 75% in the 2013 to 2014 influenza season but still remains below the Healthy People 2020 objective of 90%. Mandatory influenza immunization for all health care personnel is ethical, just, and necessary to improve patient safety. It is a crucial step in efforts to reduce health care-associated influenza infections.

Safety, immunogenicity and shedding of LAIV4 in HIV-infected and uninfected children

OBJECTIVES

HIV-infected children have poor responses to inactivated influenza vaccines. Live vaccines (LAIVs) are highly efficacious in children, but they are not used in HIV-infected children du e to limited information. We investigated the safety, immunogenicity and viral shedding of LAIV4 in HIV-infected compared with uninfected children.

DESIGN

Forty-six HIV-infected and 56 uninfected children 2 to 25 years old, who had been previously vaccinated against influenza, consented to receive a single dose of LAIV4. All grade adverse events (AEs) were recorded in the first month post-vaccination and serious AEs (SAEs) throughout the influenza season. Nasopharyngeal swabs for influenza PCR and IgA ELISA and blood for hemagglutination inhibition antibody (HAI) measurements were collected at entry, 2-5, 7-10 and 21-28 days post-vaccination.

RESULTS

The HIV-infected subjects had median CD4+ cells of 649 cells/μL and plasma HIV RNA of 20 copies/mL. AEs were similar in the two groups. There were no vaccine-related SAEs. Shedding of ≥1 vaccine virus was detected in 67% HIV-infected and 50% uninfected participants (p=0.14). HAI titers did not appreciably change, but mucosal IgA antibodies significantly increased post-vaccination in both groups. High baseline HAI and IgA antibody concentrations were associated with decreased viral shedding in controls, but not in HIV-infected subjects. Similar proportions of HIV-infected vaccinees and controls reported influenza-like illnesses (12% and 6%) throughout the season.

CONCLUSIONS

LAIV4 was equally safe and immunogenic and caused similar viral shedding in HIV-infected and uninfected children. A correlate of protection against vaccine viral shedding was not identified in HIV-infected participants, although both circulating and mucosal antibodies correlated with protection in controls.

2013 IDSA clinical practice guideline for vaccination of the immunocompromised host

An international panel of experts prepared an evidenced-based guideline for vaccination of immunocompromised adults and children. These guidelines are intended for use by primary care and subspecialty providers who care for immunocompromised patients. Evidence was often limited. Areas that warrant future investigation are highlighted.

Vaccinations for healthcare personnel: update on influenza, hepatitis B, and pertussis

PURPOSE OF REVIEW

Healthcare personnel (HCP) are at risk for exposure to and transmission of potentially life-threatening vaccine preventable diseases to patients and colleagues. The Centers for Disease Control and Advisory Committee on Immunization Practices (ACIP) recommend routine influenza immunization and maintenance of immunity to hepatitis B and pertussis, among others. In this article, we aim to review recently approved influenza vaccines, as well as address some of the issues regarding hepatitis B and pertussis vaccinations in HCP.

RECENT FINDINGS

Several new formulations of influenza vaccines are now available, including quadrivalent vaccines and non-egg-based vaccines; their use in HCP requires further study. An alarming rise in pertussis rates has led to a revision of ACIP guidelines recommending vaccination for women during each pregnancy. Persistent lack of immunity to hepatitis B after vaccine series remains a problem for many HCP.

SUMMARY

Inactivated trivalent influenza vaccines remain the safest and most widely studied influenza vaccinations for healthcare workers. A pertussis booster in the form of Tdap is now recommended for most HCP. More studies are needed regarding the issue of nonresponders in HCP who receive the three-dose hepatitis B vaccine series, as there are some promising strategies available that may boost immune responses.

Comparative study of influenza virus replication in MDCK cells and in primary cells derived from adenoids and airway epithelium

Although clinical trials with human subjects are essential for determination of safety, infectivity, and immunogenicity, it is desirable to know in advance the infectiousness of potential candidate live attenuated influenza vaccine strains for human use. We compared the replication kinetics of wild-type and live attenuated influenza viruses, including H1N1, H3N2, H9N2, and B strains, in Madin-Darby canine kidney (MDCK) cells, primary epithelial cells derived from human adenoids, and human bronchial epithelium (NHBE cells). Our data showed that despite the fact that all tissue culture models lack a functional adaptive immune system, differentiated cultures of human epithelium exhibited the greatest restriction for all H1N1, H3N2, and B vaccine viruses studied among three cell types tested and the best correlation with their levels of attenuation seen in clinical trials with humans. In contrast, the data obtained with MDCK cells were the least predictive of restricted viral replication of live attenuated vaccine viruses in humans. We were able to detect a statistically significant difference between the replication abilities of the U.S. (A/Ann Arbor/6/60) and Russian (A/Leningrad/134/17/57) cold-adapted vaccine donor strains in NHBE cultures. Since live attenuated pandemic influenza vaccines may potentially express a hemagglutinin and neuraminidase from a non-human influenza virus, we assessed which of the three cell cultures could be used to optimally evaluate the infectivity and cellular tropism of viruses derived from different hosts. Among the three cell types tested, NHBE cultures most adequately reflected the infectivity and cellular tropism of influenza virus strains with different receptor specificities. NHBE cultures could be considered for use as a screening step for evaluating the restricted replication of influenza vaccine candidates.

Live attenuated influenza vaccine (FluMist®; Fluenz™): a review of its use in the prevention of seasonal influenza in children and adults

Live attenuated influenza vaccine (LAIV) is an intranasally administered trivalent, seasonal influenza vaccine that contains three live influenza viruses (two type A [H1N1 and H3N2 subtypes] and one type B). LAIV was effective in protecting against culture-confirmed influenza caused by antigenically matched and/or distinct viral strains in children aged ≤71 months enrolled in three phase III trials. LAIV was superior to trivalent inactivated influenza vaccine (TIV) in protecting against influenza caused by antigenically-matching viral strains in a multinational phase III trial in children aged 6-59 months. LAIV was also significantly more effective than TIV in decreasing the incidence of culture-confirmed influenza illness in two open-label studies (in children with recurrent respiratory tract illnesses aged 6-71 months and in children and adolescents with asthma aged 6-17 years). LAIV did not differ significantly from placebo in preventing febrile illnesses in adults (primary endpoint) enrolled in a phase III trial. However, LAIV significantly reduced the incidence of febrile upper respiratory tract illnesses (URTI), severe febrile illnesses, febrile URTI-related work absenteeism and healthcare provider use. In another well designed trial in adults, LAIV significantly reduced the incidence of symptomatic, laboratory-confirmed influenza compared with placebo (but not intramuscular TIV). LAIV was generally well tolerated in most age groups, with the majority of adverse events being mild to moderate in severity, and runny nose/nasal congestion being the most common. In a large phase III trial, LAIV, compared with TIV, was associated with an increased incidence of medically significant wheezing in vaccine-naive children aged <24 months and an increased incidence of hospitalization in children aged 6-11 months; LAIV is not approved for use in children <24 months. LAIV was not always associated with high rates of seroconversion/seroresponse, particularly in older children and adults, or in subjects with detectable levels of haemagglutination-inhibiting antibodies at baseline. However, LAIV did elicit mucosal (nasal) IgA antibody responses and strong cell-mediated immunity responses. Only one confirmed case of LAIV virus transmission to a placebo recipient (who did not become ill) occurred in a transmission study conducted in young children. The immunogenic response to LAIV in young healthy children was not affected by concomitant administration with other commonly administered childhood vaccines. In conclusion, intranasal LAIV seasonal influenza vaccine is effective and well tolerated in children, adolescents and adults. LAIV was more effective than TIV in children, although this advantage was not seen in adults. In the US, LAIV is indicated for the active immunization of healthy subjects aged 2-49 years against influenza disease caused by virus subtypes A and type B contained in the vaccine.

Transocular entry of seasonal influenza-attenuated virus aerosols and the efficacy of n95 respirators, surgical masks, and eye protection in humans

BACKGROUND

The efficacy of barrier precautions to prevent influenza transmission is unknown.

METHODS

Twenty-eight participants were exposed to monodispersed live attenuated influenza vaccine (LAIV) particles (4.9 μm) in 6 groups: group 1, no precautions; group 2, ocular exposure only; group 3, surgical mask without eye protection; group 4, surgical mask with eye protection; group 5, fit-tested N95 respirator without eye protection; and group 6, fit-tested N95 respirator with eye protection. Influenza was detected by reverse-transcription polymerase chain reaction (RT-PCR) and culture in nasal washes. Exact 95% confidence intervals (CIs) were calculated.

RESULTS

Influenza was detected in 4 of 4 participants in group 1 (95% CI, 0-.60), 3 of 4 in group 2 (95% CI, .006-.806]), 5 of 5 in group 3 (95% CI, 0-.522), 5 of 5 in group 4, (95% CI, 0-.522), 3 of 5 in group 5 (95% CI, .053-.853), and 1 of 5 in group 6 (95% CI, .05-.72). RT-PCR revealed significant differences between group 1 and all other groups except group 3.

CONCLUSIONS

Transocular transmission of LAIV occured in most participants suggesting the necessity of eye protection. An N95 respirator provided the best guard further enhanced by eye protection.

Shedding of Ann Arbor strain live attenuated influenza vaccine virus in children 6-59 months of age

BACKGROUND

A trivalent, Ann Arbor strain, live attenuated influenza vaccine (LAIV) is approved for use in children 24 months of age and older in a number of countries. The incidence, duration, and other parameters of viral shedding after vaccination with LAIV have not been fully described in children ≤ 5 years of age.

METHODS

An open-label, single-arm, multicenter, phase 2 study assessed viral shedding and safety in 200 children 6-59 months of age after a single, intranasal dose of LAIV in 2006. Participants were enrolled into 2 age groups: 6-23 months (n=100) and 24-59 months (n=100) of age. Viral shedding, reactogenicity, and adverse events were assessed for 28 days postvaccination. Serious adverse events and significant new medical conditions were monitored for 180 days postvaccination.

RESULTS

Viral shedding was detected by culture in 79% (95% CI, 73-84) of vaccine recipients and occurred more frequently in children 6-23 months of age (89%) compared with children 24-59 months of age (69%). In total, 157 subjects shed vaccine, which was confirmed by RT-PCR as A/H1N1 for 128 subjects, A/H3N2 for 72 subjects, and B for 74 subjects. The incidence of shedding was highest on day 2 (59% in the 6-23 month age group; 41% in the 24-59 month age group) and most shedding occurred 1-11 days postvaccination; shedding after 11 days was infrequent and occurred almost exclusively in children 6-23 months of age. Mean titers of shed vaccine virus peaked on day 2 and were generally <10(3.0) median tissue culture infective dose/mL for both groups. Reactogenicity events peaked on day 2; runny/stuffy nose was reported most frequently (63% of all subjects).

CONCLUSION

Most children 6-59 months of age vaccinated with Ann Arbor strain LAIV shed ≥ 1 vaccine virus within 11 days of vaccination. Shedding was less common in children 24-59 months of age, a population for whom LAIV is approved for use. Titers of shed vaccine were low, which may explain why secondary transmission of LAIV was observed very infrequently in a previous controlled study conducted with young children in a daycare setting.

Influenza vaccines: from surveillance through production to protection

Influenza is an important contributor to population and individual morbidity and mortality. The current influenza pandemic with novel H1N1 has highlighted the need for health care professionals to better understand the processes involved in creating influenza vaccines, both for pandemic as well as for seasonal influenza. This review presents an overview of influenza-related topics to help meet this need and includes a discussion of the burden of disease, virology, epidemiology, viral surveillance, and vaccine strain selection. We then present an overview of influenza vaccine-related topics, including vaccine production, vaccine efficacy and effectiveness, influenza vaccine misperceptions, and populations that are recommended to receive vaccination. English-language articles in PubMed published between January 1, 1970, and October 7, 2009, were searched using key words human influenza, influenza vaccines, influenza A, and influenza B.

Influenza vaccination with a live attenuated vaccine

Influenza is a highly contagious, acute respiratory illness with a long history of outbreaks dating back several centuries. Although immunization is an effective means of protection against influenza, vaccination rates have been suboptimal, especially among certain high-risk groups, including children and health care personnel. This article reviews basic information about influenza and immunization, discusses the relevance of children as vectors of disease, and highlights current information on FluMist, an intranasally administered, live attenuated influenza vaccine, including studies of its use compared with trivalent inactivated vaccine and in children.

Kinetics of viral shedding and immune responses in adults following administration of cold-adapted influenza vaccine

The optimal type and timing of specimens to study the immune responses to cold-adapted influenza vaccine (CAIV) and shedding of vaccine virus are not well established. Healthy adults were vaccinated with CAIV (n=10) or trivalent influenza vaccine (TIV) (n=5). Shedding of vaccine strain influenza B was detected by culture in 6 of 10 CAIV recipients; influenza A was also detected in one of these subjects. Viral shedding by quantitative RT-PCR was detected in 9 of 10 subjects. We detected a > or = 2-fold increase in influenza-specific IgA in nasal wash in 80-100% of CAIV recipients following vaccination, but specific IgG increased in neither nasal wash nor saliva. Recipients of TIV had significant increases in specific serum IgG antibodies. Recipients of both CAIV and TIV had significant increases in IFNgamma-secreting peripheral blood mononuclear cells (PBMCs). PBMCs from subjects receiving CAIV showed a higher proportion of functional, tissue-tropic T-cells (CD4+CD69+CD18+MIP1alpha+) specific for homotypic and heterosubtypic strains of influenza by flow cytometry.

Flu myths: dispelling the myths associated with live attenuated influenza vaccine

Live attenuated influenza vaccine (LAIV), commercially available since 2003, has not gained widespread acceptance among prescribers. This underuse can be traced to several misperceptions and fears regarding LAIV. This review examines both the facts (safety, immunogenicity, and effectiveness) and the most pervasive myths about LAIV. Live attenuated influenza vaccine is a safe, highly immunogenic, and effective vaccine. It is well tolerated; only mild and transient upper respiratory infection symptoms occur with LAIV vs placebo, even in higher-risk patients with asthma or the early stages of human immunodeficiency virus. It is immunogenic, especially in induction of mucosal immunity. In certain populations, LAIV is as effective as, and in some cases more effective than, inactivated influenza in preventing influenza infection. It appears to be more effective in preventing influenza infection than trivalent inactivated influenza vaccine when the vaccine virus strain does not closely match that of the circulating wild-type virus. Many myths and misperceptions about the vaccine exist, foremost among them the myth of genetic reversion. Independent mutation in 4 gene segments would be required for reversion of the vaccine strain of influenza virus to a wild type, an unlikely and as yet unobserved event. Although shedding of vaccine virus is common, transmission of vaccine virus has been documented only in a single person, who remained asymptomatic. In the age groups for which it is indicated, LAIV is a safe and effective vaccine to prevent influenza infection.

Special immunization considerations of the preterm infant

More changes to the American Academy of Pediatrics Recommended Immunization Schedule have occurred in the past 3 years than in the previous decade. Selection of the optimal immunization regimen is essential to forestall immunization delay. New complications to the schedule pose challenges for the care of preterm infants who are at increased risk of mortality and morbidity from vaccine-preventable diseases. This article reviews the relevant data regarding immunization of preterm infants and suggests strategies for prevention of immunization delay. Protection of preterm infants, especially for pertussis and influenza, involves not just assessing a child's vaccination status but those of other close contacts and household members.

Duration of influenza A virus shedding in hospitalized patients and implications for infection control

OBJECTIVE

To assess the duration of shedding of influenza A virus detected by polymerase chain reaction (PCR) and cell culture among patients hospitalized with influenza A virus infection.

SETTING

Mayo Clinic (Rochester, Minnesota) hospitals that cater to both the community and referral populations.

METHODS

Patients 18 years old and older who were hospitalized between December 1, 2004, and March 15, 2005, with a laboratory-confirmed (ie, PCR-based) diagnosis of influenza A virus infection were consecutively enrolled. Additional throat swab specimens were collected at 2, 3, 5, and 7 days after the initial specimen (if the patient was still hospitalized). All specimens were tested by PCR and culture (both conventional tube culture and shell vial assay). Information on demographic characteristics, date of symptom onset, comorbidities, immunosuppression, influenza vaccination status, and receipt of antiviral treatment was obtained by interview and medical record review. Patients were excluded if informed consent could not be obtained or if the date of symptom onset could not be ascertained.

RESULTS

Of 149 patients hospitalized with influenza A virus infection, 50 patients were enrolled in the study. Most patients were older (median age, 76 years), and almost all (96%) had underlying chronic medical conditions. Of 41 patients included in the final analysis, influenza A virus was detected in 22 (54%) by PCR and in 12 (29%) by culture methods at or beyond 7 days after symptom onset. All 12 patients identified by culture also had PCR results positive for influenza A virus.

CONCLUSION

Hospitalized patients with influenza A virus infection can shed detectable virus beyond the 5- to 7-day period traditionally considered the duration of infectivity. Additional research is needed to assess whether prolonging the duration of patient isolation is warranted to prevent nosocomial outbreaks during the influenza season.

Mass distribution of free, intranasally administered influenza vaccine in a public school system

OBJECTIVE

School-based influenza vaccination programs are a potentially important method of protecting the community against influenza. We evaluated the feasibility and success of a large, school-based influenza vaccination campaign.

METHODS

On-site administration of intranasally administered, live attenuated influenza vaccine was offered to all students and staff members in a large, metropolitan public school system in October to December 2005. We evaluated vaccine coverage levels, resources expended, and physician and parent attitudes and knowledge.

RESULTS

Of 53,420 public school students, 24,198 were vaccinated with live attenuated influenza vaccine. Of 5841 school staff members, 3626 were vaccinated with live attenuated influenza vaccine or inactivated influenza vaccine. The proportions of students vaccinated were 56% among elementary schools, 45% among middle schools, and 30% among high schools. Schools with larger proportions of black or low-income families had lower vaccine coverage levels. The health department and school system expended 6900 person-hours during the campaign, and various health department clinics were closed for a total of 84 half-days. Community physicians were supportive of the campaign and frequently advised participation for eligible patients. Some physicians had misunderstandings about live attenuated influenza vaccine contraindications. Concern about adverse effects, having asthma, negative physician advice, and nonparticipation in any vaccination program were common reasons for students not participating.

CONCLUSIONS

This influenza vaccination campaign in a large public school system achieved relatively high vaccine coverage levels but required a substantial resource commitment from the local health department. This evaluation has critical implications for the ongoing debate regarding immunization policies for school-aged children and preparedness plans for pandemic influenza.

Risk of transmission associated with live attenuated vaccines given to healthy persons caring for or residing with an immunocompromised patient

OBJECTIVE

Persons who receive live attenuated vaccine may occasionally transmit the vaccine strain to others. The risk of such transmission is a concern, especially for persons who provide care to immunocompromised patients (ie, family and healthcare workers [HCWs]). Since the Advisory Committee on Immunization Practices released guidelines 10 years ago, several new live attenuated products have been introduced, and additional information on older vaccines has become available. To better define the risk of transmission associated with live vaccines, we reviewed the currently available literature.

RESULTS

A review of the medical literature revealed no major risk of transmission associated with any live attenuated vaccine. A theoretical risk continues to exist for the live attenuated intranasal influenza vaccine and the smallpox vaccine.

CONCLUSIONS

The available data support routine vaccination with live attenuated vaccines for all household contacts of immunocompromised patients and for HCWs caring for such patients. The benefit for immunocompromised patients of providing herd immunity against this group of potentially devastating pathogens outweighs the risk, if any, of secondary transmission.

Diagnostic discrimination of live attenuated influenza vaccine strains and community-acquired pathogenic strains in clinical samples

Live vaccines can generate false-positive results on common influenza assays including reverse transcriptase-PCR (RT-PCR), culture and antigen tests. This threatens the integrity of epidemiological data and may misdirect treatment and control efforts. We report the development of RT-PCR tests that distinguish live FluMist vaccine (FMV) strains from circulating influenza strains in clinical samples. Primers were validated using influenza-positive samples from unvaccinated patients, packaged FMV, and one PCR-positive asymptomatic vaccine. Furthermore, the assay was used to experimentally test our lab's collection of influenza-positive samples from the 2004-05 and 2005-06 influenza seasons and several 2005 preseason isolates to determine the rate of vaccine-derived false-positive results under differing epidemiological conditions. Analytical and clinical validations show that the assay is both sensitive and specific. Experimental results demonstrate that 51 out of 51 influenza-positive samples collected during influenza season from ill, previously-vaccinated military personnel represent real infections with circulating strains. Finally, the assay shows that four preseason influenza-positive samples were false positives resulting from vaccine shedding. The vaccine-discriminatory RT-PCR methods described here provide the first test designed to distinguish FMV strains from circulating strains. The results show that the test is effective, and demonstrate the importance of such tests in the age of live vaccines.