A systematic review and meta-analysis on the safety of newly adjuvanted vaccines among older adults

Age-related changes in the immune system and challenges for the development of age-specific vaccines

BACKGROUND

A better understanding of how the immune system evolves with age and how vaccines work in older people has led to increasing focus on the development of vaccines aimed specifically at older age groups. We discuss strategies used to improve vaccine immunogenicity for older adults, focusing on licensed adjuvants.

FINDINGS

With age-related immune decline (immunosenescence), older adults face increased vulnerability to infections and severe complications. Immunosenescence affects T-cell and B-cell populations and innate immunity, leading to reduced chemotaxis, cytotoxicity, and altered cytokine production. This contributes to inflammaging-low-grade, chronic inflammation linked to aging. However, immune responses vary due to genetics and life-long exposures, making chronological age an imperfect indicator of immune health. Vaccination remains key to prevention, yet immune dysfunction complicates vaccine efficacy. Strategies to enhance responses in older adults include mRNA vaccines, high-antigen content vaccines, intradermal administration, and adjuvants. mRNA COVID-19 vaccines generated strong immune responses in older adults, though lower than in younger groups. High-antigen content influenza vaccines have shown superior efficacy compared to standard vaccination. Adjuvants offer a well-established approach to boosting vaccine responses by enhancing innate immunity.

CONCLUSIONS

Of various strategies used to improve immunogenicity of vaccines for older adults, adjuvants have been the most consistently effective and practical. More recently, mRNA vaccines have also shown great promise.

Enhancing vaccine effectiveness in the elderly to counter antibiotic resistance: The potential of adjuvants via pattern recognition receptors

Vaccines are an effective way to prevent the emergence and spread of antibiotic resistance by preventing diseases and establishing herd immunity. However, the reduced effectiveness of vaccines in the elderly due to immunosenescence is one of the significant contributors to the increasing antibiotic resistance. To counteract this decline and enhance vaccine effectiveness in the elderly, adjuvants play a pivotal role. Adjuvants are designed to augment the effectiveness of vaccines by activating the innate immune system, particularly through pattern recognition receptors on antigen-presenting cells. To improve vaccine effectiveness in the elderly using adjuvants, it is imperative to select the appropriate adjuvants based on an understanding of immunosenescence and the mechanisms of adjuvant functions. This review demonstrates the phenomenon of immunosenescence and explores various types of adjuvants, including their mechanisms and their potential in improving vaccine effectiveness for the elderly, thereby contributing to developing more effective vaccines for this vulnerable demographic.

Advanced technologies for the development of infectious disease vaccines

Vaccines play a critical role in the prevention of life-threatening infectious disease. However, the development of effective vaccines against many immune-evading pathogens such as HIV has proven challenging, and existing vaccines against some diseases such as tuberculosis and malaria have limited efficacy. The historically slow rate of vaccine development and limited pan-variant immune responses also limit existing vaccine utility against rapidly emerging and mutating pathogens such as influenza and SARS-CoV-2. Additionally, reactogenic effects can contribute to vaccine hesitancy, further undermining the ability of vaccination campaigns to generate herd immunity. These limitations are fuelling the development of novel vaccine technologies to more effectively combat infectious diseases. Towards this end, advances in vaccine delivery systems, adjuvants, antigens and other technologies are paving the way for the next generation of vaccines. This Review focuses on recent advances in synthetic vaccine systems and their associated challenges, highlighting innovation in the field of nano- and nucleic acid-based vaccines.

Recommendations for Adult Immunization by the Korean Society of Infectious Diseases, 2023: Minor Revisions to the 3rd Edition

The Korean Society of Infectious Diseases has been regularly developing guidelines for adult immunization since 2007. In 2023, the guidelines for the following seven vaccines were revised: influenza, herpes zoster, pneumococcal, tetanus-diphtheria-pertussis (Tdap), human papillomavirus (HPV), meningococcal, and rabies vaccines. For the influenza vaccine, a recommendation for enhanced vaccines for the elderly was added. For the herpes zoster vaccine, a recommendation for the recombinant zoster vaccine was added. For the pneumococcal vaccine, the current status of the 15-valent pneumococcal conjugate vaccine and 20-valent PCV was described. For the Tdap vaccine, the possibility of using Tdap instead of tetanus-diphtheria vaccine was described. For the HPV vaccine, the expansion of the eligible age for vaccination was described. For the meningococcal vaccine, a recommendation for the meningococcal B vaccine was added. For the rabies vaccine, the number of pre-exposure prophylaxis doses was changed. This manuscript documents the summary and rationale of the revisions for the seven vaccines. For the vaccines not mentioned in this manuscript, the recommendations in the 3rd edition of the Vaccinations for Adults textbook shall remain in effect.

Adjuvant system AS01: from mode of action to effective vaccines

INTRODUCTION

The use of novel adjuvants in human vaccines continues to expand as their contribution to preventing disease in challenging populations and caused by complex pathogens is increasingly understood. AS01 is a family of liposome-based vaccine Adjuvant Systems containing two immunostimulants: 3-O-desacyl-4'-monophosphoryl lipid A and the saponin QS-21. AS01-containing vaccines have been approved and administered to millions of individuals worldwide.

AREAS COVERED

Here, we report advances in our understanding of the mode of action of AS01 that contributed to the development of efficacious vaccines preventing disease due to malaria, herpes zoster, and respiratory syncytial virus. AS01 induces early innate immune activation that induces T cell-mediated and antibody-mediated responses with optimized functional characteristics and induction of immune memory. AS01-containing vaccines appear relatively impervious to baseline immune status translating into high efficacy across populations. Currently licensed AS01-containing vaccines have shown acceptable safety profiles in clinical trials and post-marketing settings.

EXPERT OPINION

Initial expectations that adjuvantation with AS01 could support effective vaccine responses and contribute to disease control have been realized. Investigation of the utility of AS01 in vaccines to prevent other challenging diseases, such as tuberculosis, is ongoing, together with efforts to fully define its mechanisms of action in different vaccine settings.

Comparison of Effects of Multiple Adjuvants and Immunization Routes on the Immunogenicity and Protection of HSV-2 gD Subunit Vaccine

Genital herpes caused by herpes simplex virus type 2 (HSV-2) poses a global health issue. HSV-2 infection increases the risk of acquiring HIV infection. Studies have demonstrated that HSV-2 subunit vaccines have potential benefits, but require adjuvants to induce a balanced Th1/Th2 response. To develop a novel, effective vaccine, in this study, a truncated glycoprotein D (aa 1-285) of HSV-2 was formulated with an Al(OH)₃ adjuvant, three squalene adjuvants, MF59, AS03, and AS02, or a mucosal adjuvant, bacterium-like particles (BLPs). The immunogenicity of these subunit vaccines was evaluated in mice. After three immunizations, vaccines formulated with Al(OH)_3, MF59, AS03, and AS02 (intramuscularly) induced higher titers of neutralizing antibody than that formulated without adjuvant, and in particular, mice immunized with the vaccine plus AS02 had the highest neutralizing antibody titers and tended to produce a more balanced immune reaction than others. Intranasal gD2-PA-BLPs also induced excellent IgA levels and a more balanced Th1 and Th2 responses than intranasal gD2. After challenge with a lethal dose of HSV-2, all five adjuvants exhibited a positive effect in improving the survival rate. AS02 and gD2-PA-BLPs enhanced survival by 50% and 25%, respectively, when compared with the vaccine without adjuvant. AS02 was the only adjuvant that resulted in complete vaginal virus clearance and genital lesion healing within eight days. These results demonstrate the potential of using AS02 as a subunit vaccine adjuvant, and BLPs as a mucosal vaccine adjuvant.

Potentials of saponins-based adjuvants for nasal vaccines

Respiratory infections are a major public health concern caused by pathogens that colonize and invade the respiratory mucosal surface. Nasal vaccines have the advantage of providing protection at the primary site of pathogen infection, as they induce higher levels of mucosal secretory IgA antibodies and antigen-specific T and B cell responses. Adjuvants are crucial components of vaccine formulation that enhance the immunogenicity of the antigen to confer long-term and effective protection. Saponins, natural glycosides derived from plants, shown potential as vaccine adjuvants, as they can activate the mammalian immune system. Several licensed human vaccines containing saponins-based adjuvants administrated through intramuscular injection have demonstrated good efficacy and safety. Increasing evidence suggests that saponins can also be used as adjuvants for nasal vaccines, owing to their safety profile and potential to augment immune response. In this review, we will discuss the structure-activity-relationship of saponins, their important role in nasal vaccines, and future prospects for improving their efficacy and application in nasal vaccine for respiratory infection.

Immunogenicity of the hepatitis B vaccine adjuvanted with AS04C in patients with biological therapies

BACKGROUND

Hepatitis B vaccination is necessary for patients with biologic therapies because of the immunomodulatory effect of these drugs. Due to the elevated use of these therapies in the latest years, the research for new vaccination regimens and the improvement of the current ones is essential. New adjuvants like AS04C might be a potential strategy to improve immune response. Hepatitis B vaccine adjuvanted with AS04C has not been studied in this population before. We analyzed the immunogenicity of an adjuvanted hepatitis B vaccine in patients with biologic therapies. Variables that might affect vaccine response were also evaluated.

METHODS

Analytic observational retrospective cohort study performed between January 2016 and September 2018. 301 patients under biological treatment aged from 18 years were included. Patients received 4 doses of hepatitis B adjuvanted vaccine (Fendrix®) in a 0-1-2-6 month immunization schedule. Several sociodemographic, clinical and pharmacological variables were evaluated. The outcome variable was measured as the antibody titers (anti-HBs). The geometric mean of titers (GMT) as a measure for the central tendency was calculated from these values.

RESULTS

The immunization schedule of the hepatitis B vaccine adjuvanted with AS04C demonstrated high levels of seroconversion with 82.1 % (95 % CI, 77.6-86.6) of vaccinated patients seroconverting after primary vaccination and achieving 89.0 % (95 % IC, 85.3-92.7) after the booster doses for non-responders. The use of corticosteroid therapy and high doses of them, age over 60 years and the main diagnosis were associated with lower seroconversion rates and lower anti-HBs titers.

CONCLUSIONS

The hepatitis B vaccine adjuvanted with AS04C (Fendrix®) produces an adequate immune response in patients with autoimmune diseases and immunosuppressive and/or immunomodulating therapies. This immunization schedule is proposed as a very suitable and adapted option for the protection of patients with autoimmune diseases under active biological therapies.

Precision Vaccine Adjuvants for Older Adults: A Scoping Review

Older adults, defined as those ≥60 years of age, are a growing population vulnerable to infections including severe acute respiratory syndrome coronavirus 2. Although immunization is a key to protecting this population, immunosenescence can impair responses to vaccines. Adjuvants can increase the immunogenicity of vaccine antigens but have not been systematically compared in older adults. We conducted a scoping review to assess the comparative effectiveness of adjuvants in aged populations. Adjuvants AS01, MF59, AS03, and CpG-oligodeoxynucleotide, included in licensed vaccines, are effective in older human adults. A growing menu of investigational adjuvants, such as Matrix-M and CpG plus alum, showed promising results in early phase clinical trials and preclinical studies. Most studies assessed only 1 or 2 adjuvants and no study has directly compared >3 adjuvants among older adults. Enhanced preclinical approaches enabling direct comparison of multiple adjuvants including human in vitro modeling and age-specific animal models may derisk and accelerate vaccine development for older adults.

Effect of processed aloe vera gel on immunogenicity in inactivated quadrivalent influenza vaccine and upper respiratory tract infection in healthy adults: A randomized double-blind placebo-controlled trial

BACKGROUND

Aloe vera is a functional food with various pharmacological functions, including an immune-modulating effect. Until now, A. vera has never been studied as an adjuvant in influenza vaccine, and its effects on upper respiratory tract infection (URI) are unknown.

PURPOSE

The objective of our study was to investigate the effect of processed A. vera gel (PAG) on immunogenicity of quadrivalent inactivated influenza vaccine and URI in healthy adults.

STUDY DESIGN

A randomized, double-blind, placebo-controlled clinical trial was performed.

METHODS

This study was conducted in 100 healthy adults at a single center from September 2017 to May 2018. Subjects were randomly divided into a PAG group (n = 50) and a placebo group (n = 50). The enrolled subjects were instructed to ingest the study drug for 8 weeks. The participants received a single dose of quadrivalent inactivated influenza vaccine after taking the study drug for the first 4 weeks of the study. The primary endpoint was seroprotection rate against at least one viral strain at 4 weeks post-vaccination. Other outcomes were seroprotection rate at 24 weeks post-vaccination, seroconversion rate, geometric mean fold increase (GMFI) at 4 and 24 weeks post-vaccination, seroprotection rate ratio and geometric mean titer ratio (GMTR) at 4 weeks post-vaccination between PAG and placebo groups, and incidence, severity, and duration of URI.

RESULTS

The European Committee for proprietary medicinal products (CPMP) evaluation criteria were met at least one in the PAG and placebo groups for all strains. However, there was no significant difference in the seroprotection rate at 4 weeks post-vaccination against all strains in both PAG and placebo groups. Among secondary endpoints, the GMFI at 4 weeks post-vaccination for the A/H3N2 was significantly higher in the PAG than in placebo group. The GMTR as adjuvant effect was 1.382 (95% CI, 1.014-1.1883). Kaplan-Meier curve analysis showed a reduction in incidence of URI (p = 0.035), and a generalized estimating equation model identified a decrease in repeated URI events (odds ratio 0.57; 95% CI, 0.39-0.83; p = 0.003) in the PAG group.

CONCLUSIONS

Oral intake of PAG did not show a significant increase in seroprotection rate from an immunogenicity perspective. However, it reduced the number of URI episodes. A well-designed further study is needed on the effect of PAG's antibody response against A/H3N2 in the future.

Molecular engineering improves antigen quality and enables integrated manufacturing of a trivalent subunit vaccine candidate for rotavirus

BACKGROUND

Vaccines comprising recombinant subunit proteins are well-suited to low-cost and high-volume production for global use. The design of manufacturing processes to produce subunit vaccines depends, however, on the inherent biophysical traits presented by an individual antigen of interest. New candidate antigens typically require developing custom processes for each one and may require unique steps to ensure sufficient yields without product-related variants.

RESULTS

We describe a holistic approach for the molecular design of recombinant protein antigens-considering both their manufacturability and antigenicity-informed by bioinformatic analyses such as RNA-seq, ribosome profiling, and sequence-based prediction tools. We demonstrate this approach by engineering the product sequences of a trivalent non-replicating rotavirus vaccine (NRRV) candidate to improve titers and mitigate product variants caused by N-terminal truncation, hypermannosylation, and aggregation. The three engineered NRRV antigens retained their original antigenicity and immunogenicity, while their improved manufacturability enabled concomitant production and purification of all three serotypes in a single, end-to-end perfusion-based process using the biotechnical yeast Komagataella phaffii.

CONCLUSIONS

This study demonstrates that molecular engineering of subunit antigens using advanced genomic methods can facilitate their manufacturing in continuous production. Such capabilities have potential to lower the cost and volumetric requirements in manufacturing vaccines based on recombinant protein subunits.

Review of COVID-19 Vaccines and Their Evidence in Older Adults

Coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has resulted in a global pandemic and significant loss of life. Older people are vulnerable to SARS-CoV-2 infections and complications; thus, they are a priority group to receive COVID-19 vaccines. This review discusses considerations for COVID-19 vaccines for older adults. The general concepts of vaccine effectiveness in older adults are described, particularly immune senescence and vaccine development approaches to improve immunogenicity. The types of COVID-19 vaccine platforms are also described before reviewing the available, although limited, evidence from phase 3 COVID-19 vaccine trials relevant to older adults. The BNT162b2 vaccine by Pfizer-BioNTech and mRNA-1273 vaccine from Moderna demonstrated high efficacy and immunogenicity, which were also observed in older people. While the ChAdOx1 nCoV-19 vaccine (AZD1222) by AstraZeneca demonstrated some efficacy in older people, the vaccine dose requires clarification through further studies. Finally, the Ad26.COV2.S vaccine by Janssen Pharmaceuticals shows promise as a single-dose vaccine with a potential durability of response.

Comparing the incidence of common adverse events of interest following influenza vaccination in the first season adjuvanted trivalent immunisation was introduced: English sentinel network annual report paper 2018/19 (Preprint)

Background

Vaccination is the most effective form of prevention of seasonal influenza; the United Kingdom has a national influenza vaccination program to cover targeted population groups. Influenza vaccines are known to be associated with some common minor adverse events of interest (AEIs), but it is not known if the adjuvanted trivalent influenza vaccine (aTIV), first offered in the 2018/2019 season, would be associated with more AEIs than other types of vaccines.

Objective

We aim to compare the incidence of AEIs associated with different types of seasonal influenza vaccines offered in the 2018/2019 season.

Methods

We carried out a retrospective cohort study using computerized medical record data from the Royal College of General Practitioners Research and Surveillance Centre sentinel network database. We extracted data on vaccine exposure and consultations for European Medicines Agency–specified AEIs for the 2018/2019 influenza season. We used a self-controlled case series design; computed relative incidence (RI) of AEIs following vaccination; and compared the incidence of AEIs associated with aTIV, the quadrivalent influenza vaccine, and the live attenuated influenza vaccine. We also compared the incidence of AEIs for vaccinations that took place in a practice with those that took place elsewhere.

Results

A total of 1,024,160 individuals received a seasonal influenza vaccine, of which 165,723 individuals reported a total of 283,355 compatible symptoms in the 2018/2019 season. Most AEIs occurred within 7 days following vaccination, with a seasonal effect observed. Using aTIV as the reference group, the quadrivalent influenza vaccine was associated with a higher incidence of AEIs (RI 1.46, 95% CI 1.41-1.52), whereas the live attenuated influenza vaccine was associated with a lower incidence of AEIs (RI 0.79, 95% CI 0.73-0.83). No effect of vaccination setting on the incidence of AEIs was observed.

Conclusions

Routine sentinel network data offer an opportunity to make comparisons between safety profiles of different vaccines. Evidence that supports the safety of newer types of vaccines may be reassuring for patients and could help improve uptake in the future.

Challenges for Clinical Development of Vaccines for Prevention of Hospital-Acquired Bacterial Infections

Increasing antibiotic resistance in bacteria causing endogenous infections has entailed a need for innovative approaches to therapy and prophylaxis of these infections and raised a new interest in vaccines for prevention of colonization and infection by typically antibiotic resistant pathogens. Nevertheless, there has been a long history of failures in late stage clinical development of this type of vaccines, which remains not fully understood. This article provides an overview on present and past vaccine developments targeting nosocomial bacterial pathogens; it further highlights the specific challenges associated with demonstrating clinical efficacy of these vaccines and the facts to be considered in future study designs. Notably, these vaccines are mainly applied to subjects with preexistent immunity to the target pathogen, transient or chronic immunosuppression and ill-defined microbiome status. Unpredictable attack rates and changing epidemiology as well as highly variable genetic and immunological strain characteristics complicate the development. In views of the clinical need, re-thinking of the study designs and expectations seems warranted: first of all, vaccine development needs to be footed on a clear rationale for choosing the immunological mechanism of action and the optimal time point for vaccination, e.g., (1) prevention (or reduction) of colonization vs. prevention of infection and (2) boosting of a preexistent immune response vs. altering the quality of the immune response. Furthermore, there are different, probably redundant, immunological and microbiological defense mechanisms that provide protection from infection. Their interplay is not well-understood but as a consequence their effect might superimpose vaccine-mediated resolution of infection and lead to failure to demonstrate efficacy. This implies that improved characterization of patient subpopulations within the trial population should be obtained by pro- and retrospective analyses of trial data on subject level. Statistical and systems biology approaches could help to define immune and microbiological biomarkers that discern populations that benefit from vaccination from those where vaccines might not be effective.

Toward precision adjuvants: optimizing science and safety

PURPOSE OF REVIEW

The gradual replacement of inactivated whole cell and live attenuated vaccines with subunit vaccines has generally reduced reactogenicity but in many cases also immunogenicity. Although only used when necessary, adjuvants can be key to vaccine dose/antigen-sparing, broadening immune responses to variable antigens, and enhancing immunogenicity in vulnerable populations with distinct immunity. Licensed vaccines contain an increasing variety of adjuvants, with a growing pipeline of adjuvanted vaccines under development.

RECENT FINDINGS

Most adjuvants, including Alum, Toll-like receptor agonists and oil-in-water emulsions, activate innate immunity thereby altering the quantity and quality of an adaptive immune response. Adjuvants activate leukocytes, and induce mediators (e.g., cytokines, chemokines, and prostaglandin-E2) some of which are biomarkers for reactogenicity, that is, induction of local/systemic side effects. Although there have been safety concerns regarding a hypothetical risk of adjuvants inducing auto-immunity, such associations have not been established. As immune responses vary by population (e.g., age and sex), adjuvant research now incorporates principles of precision medicine. Innovations in adjuvant research include use of human in vitro models, immuno-engineering, novel delivery systems, and systems biology to identify biomarkers of safety and adjuvanticity.

SUMMARY

Adjuvants enhance vaccine immunogenicity and can be associated with reactogenicity. Novel multidisciplinary approaches hold promise to accelerate and de-risk targeted adjuvant discovery and development. VIDEO ABSTRACT: http://links.lww.com/MOP/A53.

High Constitutive Interleukin 10 Level Interferes With the Immune Response to Varicella-Zoster Virus in Elderly Recipients of Live Attenuated Zoster Vaccine

INTRODUCTION

Live attenuated zoster vaccine (Zostavax) was used to test the hypothesis that constitutive level of interleukin 10 (IL-10), which may be high in elderly subjects, impairs vaccine efficacy. If constitutive IL-10 impairs vaccine efficacy, the effectiveness of viral vaccines might be improved by transient inhibition of IL-10 before vaccination.

METHODS

Zostavax was given to 26 patients (age, 60-80 years). IL-10 and immunity to varicella zoster virus (VZV) were measured at baseline and after vaccination. Fluorescent antibody to membrane antigen (FAMA) assays and glycoprotein enzyme-linked immunosorbent assays (gpELISAs) were used to assess humoral immunity; anti-varicella virus T-cell responses were studied in a subset of subjects. In a prospective animal model, T-cell responses to chimeric vaccines against lymphocytic choriomeningitis virus (LCMV) were assessed in mice that express or lack IL-10.

RESULTS

FAMA assays revealed significant boosting (by 4-fold) of humoral immunity, which occurred only in subjects (10 of 26) with a low constitutive IL-10 level (ie, <20 pg/mL); moreover, the Zostavax-induced FAMA and gpELISA responses were inversely related to the constitutive IL-10 level. Significant VZV-specific T-cell responses followed vaccination only in subjects with a low constitutive IL-10 level. Vaccine-induced LCMV-specific T-cell responses in mice lacking IL-10 were greater than in wild-type animals.

CONCLUSIONS

A high constitutive IL-10 level adversely affects vaccine efficacy.

Vaccination of Adults in General Medical Practice

In vaccinating adults, clinicians face 2 types of challenges: (1) staying current on recommendations for influenza, pneumococcal, hepatitis A and B, zoster, and other vaccines and (2) addressing systemic barriers to implementing practices that increase vaccination rates. Although adult immunization rates remain suboptimal, there has been much good news in adult vaccination recently. New high-dose and adjuvanted influenza vaccines help improve immune response and may reduce influenza complications in older adults. The new recombinant zoster vaccine offers significantly more efficacy against zoster outbreaks and postherpetic neuralgia than zoster vaccine live. Pertussis vaccine given during the third trimester of pregnancy may prevent between 50% and 90% of pertussis infections in infants. Shorter time for completion (1 vs 6 months) of new, adjuvanted hepatitis B vaccine may increase adherence. Clinicians can address systemic barriers to increasing vaccination rates in their clinics and health care systems by following the Centers for Disease Control and Prevention's Standards for Adult Immunization Practice. Clinicians can help increase vaccination rates by writing standing orders and by advocating for nurses or medical assistants to receive training and protected time for assessing and documenting vaccination histories and administration. Strong recommendations that presume acceptance of vaccination are effective with most patients. Communication techniques similar to motivational interviewing can help with vaccine-hesitant patients. Clinicians, as experts on providing preventive services, can educate community leaders about the benefits of immunization and can inform vaccine experts about challenges of implementing vaccination recommendations in clinical practice and strategies that can work to raise vaccination rates.

The how's and what's of vaccine reactogenicity

Reactogenicity represents the physical manifestation of the inflammatory response to vaccination, and can include injection-site pain, redness, swelling or induration at the injection site, as well as systemic symptoms, such as fever, myalgia, or headache. The experience of symptoms following vaccination can lead to needle fear, long-term negative attitudes and non-compliant behaviours, which undermine the public health impact of vaccination. This review presents current knowledge on the potential causes of reactogenicity, and how host characteristics, vaccine administration and composition factors can influence the development and perception of reactogenicity. The intent is to provide an overview of reactogenicity after vaccination to help the vaccine community, including healthcare professionals, in maintaining confidence in vaccines by promoting vaccination, setting expectations for vaccinees about what might occur after vaccination and reducing anxiety by managing the vaccination setting.

Burden, effectiveness and safety of influenza vaccines in elderly, paediatric and pregnant populations

Vaccination is the most practical means available for preventing influenza. Influenza vaccines require frequent updates to keep pace with antigenic drift of the virus, and the effectiveness, and sometimes the safety, of the vaccine can therefore vary from season to season. Three key populations that the World Health Organization recommends should be prioritized for influenza vaccination are pregnant women, children younger than 5 years of age and the elderly. This review discusses the burden of influenza and the safety and effectiveness profile of influenza vaccines recommended for these groups.