Structural damages in adsorbed vaccines affected by freezing

Water-Soluble and Freezable Aluminum Salt Vaccine Adjuvant

Particulate aluminum salts have long occupied a central place worldwide as inexpensive immunostimulatory adjuvants that enable induction of protective immunity for vaccines. Despite their huge benefits and safety, the particulate structures of aluminum salts require transportation and storage at temperatures between 2 °C and 8 °C, and they all have exquisite sensitivity to damage caused by freezing. Here, we propose to solve the critical freezing vulnerability of particulate aluminum salt adjuvants by introducing soluble aluminum salts as adjuvants. The solubility properties of fresh and frozen aluminum chloride and aluminum triacetate, each buffered optimally with sodium acetate, were demonstrated with visual observations and with UV-vis scattering analyses. Two proteins, A244 gp120 and CRM197, adjuvanted either with soluble aluminum chloride or soluble aluminum triacetate, each buffered by sodium acetate at pH 6.5-7.4, elicited murine immune responses that were equivalent to those obtained with Alhydrogel®, a commercial particulate aluminum hydroxide adjuvant. The discovery of the adjuvanticity of soluble aluminum salts might require the creation of a new adjuvant mechanism for aluminum salts in general. However, soluble aluminum salts might provide a practical substitute for particulate aluminum salts as vaccine adjuvants, thereby avoiding the risk of inactivation of vaccines due to accidental freezing of aluminum salt particles.

Using freeze-preventive cold boxes in rural Nepal: A study of equipment performance, acceptability, system fit, and cost

We conducted a field evaluation using qualitative and quantitative methods to assess freeze prevention of vaccines transported and stored in a recently developed, World Health Organization-prequalified freeze-preventive cold box (FPCB) as compared to currently used standard cold boxes (SCBs). The study assessed the FPCB's practical use, health worker acceptance, health system fit (including cost considerations), and challenges faced by health workers in variable conditions and geographical settings. The evaluation took place in five health facilities across hilly and plains districts of Nepal in two phases: Phase 1 involved FPCBs in simulated use alongside SCBs. In Phase 2, actual vaccines were used in the FPCBs. The study gathered quantitative data from logbooks and electronic temperature monitors placed inside and outside the cold boxes. Qualitative data were collected from health workers, cold chain personnel, and immunization program managers involved in the vaccine cold chain at multiple levels. No damage, durability issues, or freezing incidents were observed when using FPCBs, but two incidents of freezing occurred when using SCBs. FPCBs also took longer to cool down than SCBs. Participants mostly found the FPCB to be safe and user friendly for vaccine transportation and short-term storage. Advantages of the FPCB as compared to the SCB include its ability to minimize vaccine wastage, to keep freeze-sensitive vaccines safe (the average value of freeze-sensitive vaccines transported per shipment was $1,704), and to ease preparation through elimination of the need to condition ice packs. Procurement price ranges for FPCBs overlap those for SCBs. Disadvantages of the FPCB include its greater size and weight, which require more personnel and vehicles during transportation. This suggests that lighter and smaller FPCBs would be more effective and acceptable for the Nepal immunization program and other, similar immunization programs conducted globally.

A Single Dose, Thermostable, Trivalent Human Papillomavirus Vaccine Formulated Using Atomic Layer Deposition

Formulations of human papillomavirus (HPV) 16, 18, and 31 L1 capsomere protein antigens were spray dried to obtain glassy microspheres that were then coated by atomic layer deposition (ALD) with nanometer-thin protective layers of alumina. Spray-drying was used to formulate human papillomavirus (HPV) 16, 18, and 31 L1 capsomere protein antigens within glassy microspheres to which nanoscopic protective layers of alumina were applied using ALD. Suspensions of alumina-coated, capsomere-containing microparticles were administered in a single dose to mice. ALD-deposited alumina coatings provided thermostability and a delayed in vivo release of capsomere antigens, incorporating both a prime and a boost dose in one injection. Total serotype-specific antibody titers as well as neutralizing titers determined from pseudovirus infectivity assays were unaffected by incubation of the ALD-coated vaccines for at 4, 50, or 70 °C for three months prior to administration. In addition, even after incubation for three months at 70 °C, single doses of ALD-coated vaccines produced both higher total antibody responses and higher neutralizing responses than control immunizations that used two doses of conventional liquid formulations stored at 4 °C.

Effects of aluminum-salt, CpG and emulsion adjuvants on the stability and immunogenicity of a virus-like particle displaying the SARS-CoV-2 receptor-binding domain (RBD)

Second-generation COVID-19 vaccines with improved immunogenicity (e.g., breadth, duration) and availability (e.g., lower costs, refrigerator stable) are needed to enhance global coverage. In this work, we formulated a clinical-stage SARS-CoV-2 receptor-binding domain (RBD) virus-like particle (VLP) vaccine candidate (IVX-411) with widely available adjuvants. Specifically, we assessed the in vitro storage stability and in vivo mouse immunogenicity of IVX-411 formulated with aluminum-salt adjuvants (Alhydrogel™, AH and Adjuphos™, AP), without or with the TLR-9 agonist CpG-1018™ (CpG), and compared these profiles to IVX-411 adjuvanted with an oil-in-water nano-emulsion (AddaVax™, AV). Although IVX-411 bound both AH and AP, lower binding strength of antigen to AP was observed by Langmuir binding isotherms. Interestingly, AH- and AP-adsorbed IVX-411 had similar storage stability profiles as measured by antigen-binding assays (competitive ELISAs), but the latter displayed higher pseudovirus neutralizing titers (pNT) in mice, at levels comparable to titers elicited by AV-adjuvanted IVX-411. CpG addition to alum (AP or AH) resulted in a marginal trend of improved pNTs in stressed samples only, yet did not impact the storage stability profiles of IVX-411. In contrast, previous work with AH-formulations of a monomeric RBD antigen showed greatly improved immunogenicity and decreased stability upon CpG addition to alum. At elevated temperatures (25, 37°C), IVX-411 formulated with AH or AP displayed decreased in vitro stability compared to AV-formulated IVX-411and this rank-ordering correlated with in vivo performance (mouse pNT values). This case study highlights the importance of characterizing antigen-adjuvant interactions to develop low cost, aluminum-salt adjuvanted recombinant subunit vaccine candidates.

Assessing Antigen-Adjuvant Complex Stability Against Physical Stresses By wNMR

This study applies an emerging analytical technology, wNMR (water proton nuclear magnetic resonance), to assess the stability of aluminum adjuvants and antigen-adjuvant complexes against physical stresses, including gravitation, flow and freeze/thaw. Results from wNMR are verified by conventional analytical technologies, including static light scattering and microfluidic imaging. The results show that wNMR can quickly and noninvasively determine whether an aluminum adjuvant or antigen-adjuvant complex sample has been altered by physical stresses.

New formulation of a recombinant anthrax vaccine stabilised with structurally modified plant viruses

Anthrax is a disease caused by Bacillus anthracis. The most promising approach to the development of anthrax vaccine is use of the anthrax protective antigen (PA). At the same time, recombinant PA is a very unstable protein. Previously, the authors have designed a stable modified recombinant anthrax protective antigen with inactivated proteolytic sites and substituted deamidation sites (rPA83m). As a second approach to recombinant PA stabilisation, plant virus spherical particles (SPs) were used as a stabiliser. The combination of these two approaches was shown to be the most effective. Here, the authors report the results of a detailed study of the stability, immunogenicity and protectiveness of rPA83m + SPs compositions. These compositions were shown to be stable, provided high anti-rPA83m antibody titres in guinea pigs and were able to protect them from a fully virulent 81/1 Bacillus anthracis strain. Given these facts, the formulation of rPA83m + SPs compositions is considered to be a prospective anthrax vaccine candidate.

Mechanistic elucidation of freezing-induced surface decomposition of aluminum oxyhydroxide adjuvant

The freezing-induced aggregation of aluminum-based (Alum) adjuvants has been considered as the most important cause of reduced vaccine potency. However, the intrinsic properties that determine the functionality of Alum after freezing have not been elucidated. In this study, we used engineered aluminum oxyhydroxide nanoparticles (AlOOH NPs) and demonstrated that cryogenic freezing led to the mechanical pressure-mediated reduction of surface hydroxyl. The sugar-based surfactant, octyl glucoside (OG), was demonstrated to shield AlOOH NPs from the freezing-induced loss of hydroxyl content and the aggregation through the reduction of recrystallization-induced mechanical stress. As a result, the antigenic adsorption property of frozen AlOOH NPs could be effectively protected. When hepatitis B surface antigen (HBsAg) was adjuvanted with OG-protected frozen AlOOH NPs in mice, the loss of immunogenicity was inhibited. These findings provide insights into the freezing-induced surface decomposition of Alum and can be translated to design of protectants to improve the stability of vaccines.

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The freezing stress led to the destruction of surface hydroxyl group on AlOOH NPs

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Octyl glucoside protected AlOOH NPs from freezing-induced surface decomposition

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Octyl glucoside protected vaccines from freezing-induced loss of immunogenicity

Evaluation of precipitation time of the aluminum salts adsorbed potentially frozen vaccines used in the Polish National Immunization Schedule for their pre-qualification before the administration

Purpose

Vaccines adsorbed on aluminum adjuvants irreversibly lose potency after freezing and their safety is affected. To prevent the administration of such vaccines, the World Health Organization developed the Shake Test designed to determine whether adsorbed vaccines have been frozen or not. However, the Shake Test is difficult and time-consuming when routinely conducted at the place of vaccination. In this study, a modified shake test for prequalification of potentially frozen vaccines was elaborated.

Materials and Methods

Vaccines used in the Polish Immunization Schedule were investigated and the analysis includes an assessment of precipitation time and the influence of the container type, amount and type of aluminum compound, and a volume of vaccine dose on the precipitation time.

Results

Significant differences between the precipitation time of frozen and non-frozen vaccines routinely used in the Polish Immunization Schedule were observed. The precipitation time of all non-frozen vaccines was above 30 minutes. The longest precipitation time of frozen vaccines was 10 minutes.

Conclusion

The finding of the study can be used in practice by the personnel administering vaccines to patients. Step-by-step recommendations for the preparation of the test have been proposed in the article.

Diphtheria-tetanus-pertussis vaccine: past, current & future

The diphtheria-tetanus-pertussis (DTP) vaccine can prevent diphtheria, tetanus and pertussis. The component antigens of the DTP vaccine had long been monovalent vaccines. The pertussis vaccine was licensed in 1914. The same year, the mixtures of diphtheria toxin and antitoxin were put into use. In 1926, alum-precipitated diphtheria toxoid was registered, and in 1937 adsorbed tetanus toxoid was put on the market. The development of numerous effective DTP vaccines quickly stimulated efforts to combine DTP with other routine vaccines for infants. This overview covers the most important information regarding the invention of DTP vaccines, their modifications and the needs that should be focused on in the future.

RG1-VLP and Other L2-Based, Broad-Spectrum HPV Vaccine Candidates

Licensed human papillomavirus (HPV) vaccines contain virus-like particles (VLPs) self-assembled from L1 major-capsid proteins that are remarkably effective prophylactic immunogens. However, the induced type-restricted immune response limits coverage to the included vaccine types, and costly multiplex formulations, restrictive storage and distribution conditions drive the need for next generation HPV vaccines. Vaccine candidates based upon the minor structural protein L2 are particularly promising because conserved N-terminal epitopes induce broadly cross-type neutralizing and protective antibodies. Several strategies to increase the immunological potency of such epitopes are being investigated, including concatemeric multimers, fusion to toll-like receptors ligands or T cell epitopes, as well as immunodominant presentation by different nanoparticle or VLP structures. Several promising L2-based vaccine candidates have reached or will soon enter first-in-man clinical studies. RG1-VLP present the HPV16L2 amino-acid 17–36 conserved neutralization epitope “RG1” repetitively and closely spaced on an immunodominant surface loop of HPV16 L1-VLP and small animal immunizations provide cross-protection against challenge with all medically-significant high-risk and several low-risk HPV types. With a successful current good manufacturing practice (cGMP) campaign and this promising breadth of activity, even encompassing cross-neutralization of several cutaneous HPV types, RG1-VLP are ready for a first-in-human clinical study. This review aims to provide a general overview of these candidates with a special focus on the RG1-VLP vaccine and its road to the clinic.

Monitoring of the sedimentation kinetics of vaccine adjuvants using water proton NMR relaxation

Suspensions of solid particles find applications in many areas-mining, waste treatment, and in pharmaceutical formulations. Pharmaceutical suspensions include aluminum-adjuvanted vaccines are widely administered to millions of people worldwide annually. Hence, the stability parameters of such suspensions, for example, sedimentation rate and the compactness of the formed sediments, are of great interest to achieve the most optimal and stable formulations. Unlike currently used analytical techniques involving visual observations and/or monitoring of several optical properties using specialized glassware, water proton nuclear magnetic resonance (wNMR) used in this work allows one to analyze samples in their original sealed container regardless of its opacity and/or labeling. It was demonstrated that the water proton transverse relaxation rate could be used to monitor in real time the sedimentation process of two widely used aluminum adjuvants-Alhydrogel® and Adju-Phos®. Using wNMR, we obtained valuable information on the sedimentation rate, dynamics of the supernatant and sediment formation, and the sedimentation volume ratio (SVR) reflecting the compactness of the formed sediment. Results on SVR from wNMR were verified by caliper measurements. Verification of the sedimentation rate results from wNMR by other analytical techniques is challenging due to differences in the measured attributes and even units of the reported rate. Nonetheless, our results demonstrate the practical applicability of wNMR as an analytical tool to study pharmaceutical suspensions, for example, aluminum-adjuvanted vaccines, to provide higher quality and more efficient vaccines. Such analyses could be carried out in the original container of a suspension drug product to study its colloidal stability and to monitor its quality over time without compromising product integrity.

Effect of freezing on recombinant hepatitis E vaccine

Studies have revealed that vaccines are more often exposed to sub-zero temperatures during cold chain transportation than what was previously known. Such exposure might be detrimental to the potency of temperature-sensitive vaccines. The aim of this study was to evaluate the impact of exposure to freezing on the physicochemical properties and biological activities of recombinant hepatitis E (rHE) vaccine. Changes in rHE vaccine due to freezing temperatures were analyzed with regard to sedimentation rate, antigenicity, and antibody affinity and potency. The freezing temperature of rHE was measured, then rHE vaccine was exposed to freezing temperatures below -10°C.Significant increase of sedimentation rate was noted, according to shake test and massed precipitates. In addition, the binding affinity of rHE vaccine to six specific monoclonal antibodies was significantly reduced and the in vivo potency for eliciting a protective IgG response was also partially lost, especially for anti-HEV neutralizing antibodies. Altogether, our work indicates that exposure of rHE vaccine to a temperature below -10°C results in the loss of structural integrity and biological potency of rHE vaccine.

Comparative immunogenicity and efficacy of thermostable (lyophilized) and liquid formulation of anthrax vaccine candidate AV7909

The anthrax vaccine candidate AV7909 is being developed as a next-generation vaccine for a post-exposure prophylaxis (PEP) indication against anthrax. AV7909 consists of the anthrax vaccine adsorbed (AVA) (Emergent BioSolutions Inc., Lansing, MI) bulk drug substance adjuvanted with the immunostimulatory oligodeoxynucleotide (ODN) compound, CPG 7909. The addition of CPG 7909 to AVA enhances both the magnitude and the kinetics of antibody responses in animals and human subjects, making AV7909 a suitable next-generation vaccine for use in a PEP setting. Emergent has produced a thermostable (lyophilized) formulation of AV7909 vaccine utilizing drying technology. The purpose of the study described here was to assess the immunogenicity and efficacy of the lyophilized formulation of the AV7909 vaccine candidate as compared with the liquid formulation in the guinea pig general-use prophylaxis (GUP) model. The study also provides initial information on the relationship between the immune response induced by the thermostable formulation of the vaccine, as measured by the toxin neutralization assay (TNA), and animal survival following lethal anthrax aerosol challenge. Results demonstrated that there were no significant differences in the immunogenicity or efficacy of lyophilized AV7909 against lethal anthrax spore aerosol challenge in the guinea pig model as compared to liquid AV7909. For both vaccine formulations, logistic regression modeling showed that the probability of survival increased as the pre-challenge antibody levels increased.

On-farm storage of livestock vaccines may be a risk to vaccine efficacy: a study of the performance of on-farm refrigerators to maintain the correct storage temperature

BACKGROUND

Livestock vaccines (LV) are often stored on-farm, in a refrigerator (fridge), prior to use and little is documented about the storage conditions during this period. As the quality of a vaccine can be impaired by storage at an incorrect temperature, the present study aimed to evaluate the on-farm performance of farm fridges to maintain the correct storage temperature. From January to August 2014, temperature data loggers were placed on selected farms fridges used to store LV (n = 20) in South-West England.

RESULTS

Temperature recording data was available from 17 of the 20 farms. Fifty-nine percent of farm fridges had at least one temperature recording above 8 °C, 53% had at least one recording below 2 °C and 41% at or below 0 °C. Internal fridge temperatures attained 24 °C and dropped to - 12 °C as an absolute maximum and minimum respectively. Fridges tested spent an average of 16% of the total time recorded above 8 °C. Time of the year significantly influenced the percentage of time above 8 °C. External and internal temperatures were found to be positively correlated (p < 0.001). Statistical significant differences in internal and external temperatures were found between March and August.

CONCLUSIONS

The majority of fridges in this study would have failed to keep any stored LV within the recommended storage temperature range. If LV are going to be stored on-farm prior to use, then urgent improvements in this part of the cold-chain are required in order to insure vaccine efficacy is not compromised.

Safety of vaccines that have been kept outside of recommended temperatures: Reports to the Vaccine Adverse Event Reporting System (VAERS), 2008-2012

BACKGROUND

Vaccines should be stored and handled according to manufacturer specifications. Inadequate cold chain management can affect potency; but, limited data exist on adverse events (AE) following administration of vaccines kept outside of recommended temperatures.

OBJECTIVE

To describe reports to the Vaccine Adverse Event Reporting System (VAERS) involving vaccines inappropriately stored outside of recommended temperatures and/or exposed to temperatures outside of manufacturer specifications for inappropriate amounts of time.

METHODS

We searched the VAERS database (analytic period 2008-2012) for reports describing vaccines kept outside of recommended temperatures. We analyzed reports by vaccine type, length outside of recommended temperature and type of temperature excursion, AE following receipt of potentially compromised vaccine, and reasons for cold chain breakdown.

RESULTS

We identified 476 reports of vaccines kept outside of recommended temperatures; 77% described cluster incidents involving multiple patients. The most commonly reported vaccines were quadrivalent human papillomavirus (n = 146, 30%), 23-valent pneumococcal polysaccharide (n = 51, 11%), and measles, mumps, and rubella (n = 45, 9%). Length of time vaccines were kept outside of recommended temperatures ranged from 15 mins to 6 months (median 51 h). Most (n = 458, 96%) reports involved patients who were administered potentially compromised vaccines; AE were reported in 32 (7%), with local reactions (n = 21) most frequent. Two reports described multiple patients contracting diseases they were vaccinated against, indicating possible influenza vaccine failure. Lack of vigilance, inadequate training, and equipment failure were reasons cited for cold chain management breakdowns.

CONCLUSIONS

Our review does not indicate any substantial direct health risk from administration of vaccines kept outside of recommended temperatures. However, there are potential costs and risks, including vaccine wastage, possible decreased protection, and patient and parent inconvenience related to revaccination. Maintaining high vigilance, proper staff training, regular equipment maintenance, and having adequate auxiliary power are important components of comprehensive vaccine cold chain management.

Good vaccination practice: it all starts with a good vaccine storage temperature

Background

Recent introduction of strategies to reduce antibiotic use in food animal production implies an increased use of vaccines in order to prevent the economic impact of several important diseases in swine. Good Vaccination Practice (GVP) is an overall approach on the swine farm aiming to obtain maximal efficacy of vaccination through good storage, preparation and finally correct application to the target animals. In order to have a better insight into GVP on swine farms and the vaccine storage conditions, a survey on vaccination practices was performed on a farmers’ fair and temperatures in the vaccine storage refrigerators were measured during farm visits over a period of 1 year.

Results

The survey revealed that knowledge on GVP, such as vaccine storage and handling, needle management and injection location could be improved. Less than 10% had a thermometer in their vaccine storage refrigerator on the moment of the visit. Temperature measurement revealed that only 71% of the measured refrigerators were in line with the recommended temperature range of +2 °C to +8 °C. Both below +2 °C and above +8 °C temperatures were registered during all seasons of the year. Compliance was lower during summer with an average temperature of 9.2 °C while only 43% of the measured temperatures were within the recommended range.

Conclusions

The present study clearly showed the need for continuous education on GVP for swine veterinarians, swine farmers and their farm personnel in general and vaccine storage management in particular. In veterinary medicine, the correct storage of vaccines is crucial since both too low and too high temperatures can provoke damage to specific vaccine types. Adjuvanted killed or subunit vaccines can be damaged (e.g. structure of aluminiumhydroxide in adjuvans) by too low temperatures (below 0 °C), whereas lyophilized live vaccines are susceptible (e.g. loss of vaccine potency) to heat damage by temperatures above +8 °C. In conclusion, knowledge and awareness of GVP and vaccine storage conditions are crucial under practical field conditions in swine herds. Focus on a correct on-farm vaccine storage is part of the responsible veterinarians’ guidance in order to obtain the required vaccine efficacy.

Adjuvant formulations for virus-like particle (VLP) based vaccines

The development of virus-like particle (VLP) technology has had an enormous impact on modern vaccinology. In order to optimize the efficacy and safety of VLP-based vaccines, adjuvants are included in most vaccine formulations. To date, most licensed VLP-based vaccines utilize the classic aluminum adjuvant compositions. Certain challenging pathogens and weak immune responder subjects may require further optimization of the adjuvant formulation to maximize the magnitude and duration of the protective immunity. Indeed, novel classes of adjuvants such as liposomes, agonists of pathogen recognition receptors, polymeric particles, emulsions, cytokines and bacterial toxins, can be used to further improve the immunostimulatory activity of a VLP-based vaccine. This review describes the current advances in adjuvant technology for VLP-based vaccines directed at viral diseases, and discusses the basic principles for designing adjuvant formulations for enhancing the vaccine immunogenicity.

Mineral Adjuvants∗∗The present chapter is an updated version of the chapter “Mineral Adjuvants,” published in Immunopotentiators in Modern Vaccines, p. 217–233. Ed. Virgil Schijns & Derek O'Hagan, Elsevier Science Publishers (2005)

Mineral adjuvants comprise aluminum hydroxide and phosphate adjuvants as well as calcium phosphate adjuvants. In particular, the aluminum salts have achieved an undisputed status as the most commonly used adjuvants in human and veterinary vaccines. Calcium phosphate adjuvant, later discovered by Edgar Relyveld, constitutes a very interesting alternative and has also been applied both in human and veterinary vaccines. New analytical tools applied in adjuvant research are about to take us to the next level of understanding mineral adjuvants. These tools have been used to characterize mineral adjuvants, but so far, in particular, aluminum-based adjuvants in terms of surface marker expression profiles, isotypic profiles, and cytokine profiles. In the past 10 years, the discovery of adjuvant-mediated induction of the NALP3 inflammasome and its impact on the secretion of interleukin (IL)-1β and IL-18 as proinflammatory mediators in the early phases of immune response has been described as an important mechanism for the function of these adjuvants.

Formulation and stabilization of recombinant protein based virus-like particle vaccines

Vaccine formulation development has traditionally focused on improving antigen storage stability and compatibility with conventional adjuvants. More recently, it has also provided an opportunity to modify the interaction and presentation of an antigen/adjuvant to the immune system to better stimulate the desired immune responses for maximal efficacy. In the last decade, there has been a paradigm shift in vaccine antigen and formulation design involving an improved physical understanding of antigens and a better understanding of the immune system. In addition, the discovery of novel adjuvants and delivery systems promises to further improve the design of new, more effective vaccines. Here we describe some of the fundamental aspects of formulation design applicable to virus-like-particle based vaccine antigens (VLPs). Case studies are presented for commercially approved VLP vaccines as well as some investigational VLP vaccine candidates. An emphasis is placed on the biophysical analysis of vaccines to facilitate formulation and stabilization of these particulate antigens.

Development of a highly thermostable, adjuvanted human papillomavirus vaccine

A major impediment to economical, worldwide vaccine distribution is the requirement for a "cold chain" to preserve antigenicity. We addressed this problem using a model human papillomavirus (HPV) vaccine stabilized by immobilizing HPV16 L1 capsomeres, i.e., pentameric subunits of the virus capsid, within organic glasses formed by lyophilization. Lyophilized glass and liquid vaccine formulations were incubated at 50°C for 12weeks, and then analyzed for retention of capsomere conformational integrity and the ability to elicit neutralizing antibody responses after immunization of BALB/c mice. Capsomeres in glassy-state vaccines retained tertiary and quaternary structure, and critical conformational epitopes. Moreover, glassy formulations adjuvanted with aluminum hydroxide or aluminum hydroxide and glycopyranoside lipid A were not only as immunogenic as the commercially available HPV vaccine Cervarix®, but also retained complete neutralizing immunogenicity after high-temperature storage. The thermal stability of such adjuvanted vaccine powder preparations may thus eliminate the need for the cold chain.

Glassy-state stabilization of a dominant negative inhibitor anthrax vaccine containing aluminum hydroxide and glycopyranoside lipid A adjuvants

During transport and storage, vaccines may be exposed to temperatures outside of the range recommended for storage, potentially causing efficacy losses. To better understand and prevent such losses, dominant negative inhibitor (DNI), a recombinant protein antigen for a candidate vaccine against anthrax, was formulated as a liquid and as a glassy lyophilized powder with the adjuvants aluminum hydroxide and glycopyranoside lipid A (GLA). Freeze-thawing of the liquid vaccine caused the adjuvants to aggregate and decreased its immunogenicity in mice. Immunogenicity of liquid vaccines also decreased when stored at 40°C for 8 weeks, as measured by decreases in neutralizing antibody titers in vaccinated mice. Concomitant with efficacy losses at elevated temperatures, changes in DNI structure were detected by fluorescence spectroscopy and increased deamidation was observed by capillary isoelectric focusing (cIEF) after only 1 week of storage of the liquid formulation at 40°C. In contrast, upon lyophilization, no additional deamidation after 4 weeks at 40°C and no detectable changes in DNI structure or reduction in immunogenicity after 16 weeks at 40°C were observed. Vaccines containing aluminum hydroxide and GLA elicited higher immune responses than vaccines adjuvanted with only aluminum hydroxide, with more mice responding to a single dose.

Tools and approaches to ensure quality of vaccines throughout the cold chain

The Expanded Program on Immunization was designed 40 years ago for two types of vaccines: those that are heat stable but freeze sensitive and those that are stable to freezing but heat labile. A cold chain was developed for transport and storage of such vaccines and established in all countries, despite limited access to resources and electricity in the poorest areas. However, cold chain problems occur in all countries. Recent changes to vaccines and vaccine handling include development and introduction of new vaccines with a wide range of characteristics, improvement of heat stability of several basic vaccines, observation of vaccine freezing as a real threat, development of regulatory pathways for both vaccine development and the supply chain, and emergence of new temperature monitoring devices that can pinpoint and avoid problems. With such tools, public health groups have now encouraged development of vaccines labeled for use in flexible cold chains and these tools should be considered for future systems.

Vaccine instability in the cold chain: mechanisms, analysis and formulation strategies

Instability of vaccines often emerges as a key challenge during clinical development (lab to clinic) as well as commercial distribution (factory to patient). To yield stable, efficacious vaccine dosage forms for human use, successful formulation strategies must address a combination of interrelated topics including stabilization of antigens, selection of appropriate adjuvants, and development of stability-indicating analytical methods. This review covers key concepts in understanding the causes and mechanisms of vaccine instability including (1) the complex and delicate nature of antigen structures (e.g., viruses, proteins, carbohydrates, protein-carbohydrate conjugates, etc.), (2) use of adjuvants to further enhance immune responses, (3) development of physicochemical and biological assays to assess vaccine integrity and potency, and (4) stabilization strategies to protect vaccine antigens and adjuvants (and their interactions) during storage. Despite these challenges, vaccines can usually be sufficiently stabilized for use as medicines through a combination of formulation approaches combined with maintenance of an efficient cold chain (manufacturing, distribution, storage and administration). Several illustrative case studies are described regarding mechanisms of vaccine instability along with formulation approaches for stabilization within the vaccine cold chain. These include live, attenuated (measles, polio) and inactivated (influenza, polio) viral vaccines as well as recombinant protein (hepatitis B) vaccines.

Freeze-thaw stress of Alhydrogel ® alone is sufficient to reduce the immunogenicity of a recombinant hepatitis B vaccine containing native antigen

Preventing losses in vaccine potency due to accidental freezing has recently become a topic of interest for improving vaccines. All vaccines with aluminum-containing adjuvants are susceptible to such potency losses. Recent studies have described excipients that protect the antigen from freeze-induced inactivation, prevent adjuvant agglomeration and retain potency. Although these strategies have demonstrated success, they do not provide a mechanistic understanding of freeze-thaw (FT) induced potency losses. In the current study, we investigated how adjuvant frozen in the absence of antigen affects vaccine immunogenicity and whether preventing damage to the freeze-sensitive recombinant hepatitis B surface antigen (rHBsAg) was sufficient for maintaining vaccine potency. The final vaccine formulation or Alhydrogel(®) alone was subjected to three FT-cycles. The vaccines were characterized for antigen adsorption, rHBsAg tertiary structure, particle size and charge, adjuvant elemental content and in-vivo potency. Particle agglomeration of either vaccine particles or adjuvant was observed following FT-stress. In vivo studies demonstrated no statistical differences in IgG responses between vaccines with FT-stressed adjuvant and no adjuvant. Adsorption of rHBsAg was achieved; regardless of adjuvant treatment, suggesting that the similar responses were not due to soluble antigen in the frozen adjuvant-containing formulations. All vaccines with adjuvant, including the non-frozen controls, yielded similar, blue-shifted fluorescence emission spectra. Immune response differences could not be traced to differences in the tertiary structure of the antigen in the formulations. Zeta potential measurements and elemental content analyses suggest that FT-stress resulted in a significant chemical alteration of the adjuvant surface. This data provides evidence that protecting a freeze-labile antigen from subzero exposure is insufficient to maintain vaccine potency. Future studies should focus on adjuvant protection. To our knowledge, this is the first study to systematically investigate how FT-stress to adjuvant alone affects immunogenicity. It provides definitive evidence that this damage is sufficient to reduce vaccine potency.