Nasal Vaccine

15.5.1 Nasal drops

Nasal drops are convenient and the most simple method for delivery of nasal vaccines. The nasal drops are administered using a nasal dropper or syringes. The major disadvantage of this system is the lack of dose precision¹⁰⁷ and difficulty for the pediatric population. Some studies reported that nasal drops deposit human serum albumin in the nostrils more efficiently than nasal sprays.¹⁰⁸

15.5.2 Nasal powder

Nasal powder formulations are highly stable compared to liquid formulations. Nasal powders can extend the residence time for powder formulations on the nasal mucosa, potentially increasing the local and systemic immune response.¹⁰⁹ However, the production of nasal dry powders is quite complicated with required particle size, particle distribution, and performance characteristics when compared with other dosage forms.

15.5.3 Aerosol

The aerosol route of delivery of vaccines is one of the most preferred for nasal administration compared with other nasal dosage forms and also less reactogenic than the subcutaneous route of administration.¹¹⁰ Aerosol vaccination via the lungs targets an epithelium critical to host defense against inhaled pathogens and provides an exciting opportunity in the development of newer and more effective tuberculosis (TB), measles, and influenza vaccines. An aerosol vaccination usually depends on the target pathogen and the sites of the inductive immunity. The aerosols are available in liquid (solution, suspension, and emulsion) and solid forms. In addition to vaccine antigens, carrier/solvent, emulsifier/surfactants, corrosion inhibitors, and propellant selection and compatability play a critical role in achieving required immunogenicity in infants. Aerosol vaccine immunogenecity achievement is based on antigen particle size for prevention of upper respiratory (eg, Boredetella pertussis, Chlamydia pneumonia) and lower respiratory (eg, Streptococcus pneumoniae, Bacillus anthracis) bacteria and virus disease. Larger particles (∼5 μm) are needed for the aerosol vaccination to prevent upper respiratory tract infection and smaller particles (≤ 3 μm) for lower respiratory tract infection.¹¹¹ The dried forms of vaccines with optimum particle size are traditionally prepared by freeze drying or spray drying. The aerosol form of vaccines was administered to many human subjects for a longer period and found to provide excellent protection for diseases such as influenza A and measles.^112,113 Therefore aerosol immunization may be a promising method of vaccination.

15.5.4 Nasal gel

Nasal gels are generally used for colds, allergies, low humidity, or overuse of decongestant. Nasal vaccine gels are a high-viscosity solution or suspension in which antigenic molecules are dispersed. The advantages of a nasal gel include the reduction of nasal clearance and anterior leakage due to highly viscous formulation, reduction of irritation by using soothing/emollient excipients, and target delivery to mucosa for better absorption.¹¹⁴ In addition, it may potentially enhance the immune response, reduce the antigen and/or adjuvant dose, sustain antigen release, and improve antigen uptake with enhanced antigen stability. Special application techniques are required for the administration of nasal gel vaccines because of their highly viscous formulation and poor spreading abilities. A wide variety of gelling polymers are available for formulation such as pullulan, deaceylated gellan gum, xantham gum, chitosan, and polyethylene glycol, used to encapsulate vaccine/adjuvant formulation as gel particles. Viscosity, sol-gel transition temperature and gelling time, and gel strength and its texture are critical parameters in the development of nasal gel vaccines. Recently, pneumococcal surface protein-A nasal gel vaccine,¹¹⁵ Clostridium botulinum type-A neurotoxin BoHc/A, and tetanus toxoid¹¹⁶ were studied in animal models and enhanced both humoral and cellular immunity. Nasal gel is an alternative and promising novel dosage delivery system to achieve the immune response.

Nasal Influenza Vaccine

In nasal mucosa of unvaccinated adult subjects, antibody-producing PCs with specificity for influenza virus are present (Brokstad et al., 2001), but it remains unknown whether they are induced by previous (subclinical?) infection or vaccination, or simply reflect cross-reactivity of the mucosal IgA system. Notably, parenteral immunization with an inactivated trivalent virus vaccine did not result in a detectable increase of influenza-specific PCs in nasal mucosa (Brokstad et al., 2002), although an IgA response was elicited in tonsils and saliva (Brokstad et al., 1995; El-Madhun et al., 1998). The potential advantage of nasal immunization is illustrated by the protection achieved. Although parenteral vaccination is generally recommended in vulnerable subjects, this approach induces little or no cross-protection. Thus, there is a continuing need for interpandemic manufacturing of the actual vaccines; when a genomic drift occurs in a virus, the vaccine strain must be replaced, and it usually takes at least 6 months before a new vaccine is available.

Conversely, many studies in experimental animals and humans have demonstrated that nasal vaccination gives rise to cross-protection against drifted strains (Brandtzaeg, 2007). With an available live attenuated influenza vaccine for intranasal administration (FluMist^®), good protection was achieved despite the fact that the epidemic strain was not part of the vaccine (Belshe et al., 2000). Also, cross-clade immunity against experimentally applied HIV in mice has been reported after nasal DNA prime followed by nasal peptide boost; the vaccine contained epitopes of clade B, but high and long-lasting serum antibody titers against the neutralizing gp41 ELDKWAS epitopes from both clades A, B, C, and D were observed (Devito et al., 2004).

The efficacy and effectiveness of a trivalent, live attenuated nasal spray influenza vaccine (CAIV-T) have been documented both in healthy children and in adults (Glezen, 2002). Although nasal vaccination also efficiently induces systemic immunity, a combination of intranasal and parenteral immunization may be preferable for optimal protection when an inactivated influenza vaccine is used (Keitel et al., 2001). Alternatively, the effect of subunit vaccines applied topically can be enhanced by incorporation into liposomes or with the addition of a nontoxic mucosal adjuvant (Eurocine^®). Adjuvantation of nasal vaccines with mucoadhesive polymers such as chitosan derivatives has been promising in mouse experiments (Hagenaars et al., 2010), particularly when combined with antigen-loaded nanoparticles (Slütter et al., 2010).

Alternative Approaches

A dense population of putative APCs with a macrophage or DC phenotype exists in and below the normal surface epithelium of human nasal mucosa (Jahnsen et al., 2004). The above results suggest that to stimulate a regional immune response, a vaccine should be targeted both against these cells—which may migrate to the cervical lymph nodes—and against the crypts with M cells characteristic of NALT structures, probably the adenoids in particular (Figure 14). Such local B-cell induction apparently imprints the necessary homing properties of the primed cells to extravasate efficiently in airway mucosa and associated glands and give rise to secretory immunity at these regional effector sites (Johansen et al., 2005; Quiding-Järbrink et al., 1997). As discussed previously, the NALT-derived plasmablasts may to some extent reach the uterine cervix mucosa but do not express sufficient gut-homing molecules to enter consistently the intestinal lamina propria, particularly not in the small bowel.

The amount of antigen reaching the lymphoid tissue of Waldeyer’s ring and cervical lymph nodes after parenteral immunization is clearly insufficient to induce a protective nasal immune response, although some SIgA antibodies may occur in nasopharyngeal secretions. This most likely reflects local production in the adenoids where, as pointed out earlier, epithelial expression of pIgR/SC exists, in contrast to the palatine tonsils (Figures 11 and 12(a,b)). There is considerable communication in terms of memory/effector B-cell distribution between the mucosal and the systemic immune systems, particularly so in cervical lymph nodes and Waldeyer’s lymphoid ring because of shared homing molecules as discussed in a previous section (Figure 14).

The initial optimism regarding E. coli heat-labile enterotoxin as an adjuvant in humans (de Bernardi di Valserra et al., 2002) vanished with the occurrence of Bell’s palsy after nasal application of an adjuvanted inactivated influenza vaccine (Nasalflu^®) (Mutsch et al., 2004). This problem apparently reflects the possibility for toxins to enter the central nervous system from the olfactory bulb or cause temporary irritation and swelling of nerves going through bony canals to the brain. Other adjuvants such as the hydrophobic outer-membrane protein preparations (proteosomes) from N. meningitidis may be an efficient and safe alternative (Berstad et al., 2000; Plante et al., 2001; Treanor et al., 2006). In mice, the uptake of proteosomes can be enhanced by incorporation of the TLR2 ligand PorB (Chabot et al., 2007), but it remains to be shown whether TLRs are expressed on M cells or other parts of the follicle-associated epithelium in human NALT. Finally, virus-derived particles may function without adjuvants as demonstrated for a trivalent inactivated whole-cell influenza vaccine (Greenbaum et al., 2002)—probably because of enhanced targeting to M cells and DCs. However, a more recent clinical trial reported superior efficacy of the live attenuated influenza vaccine in children 12–59 months of age—for both antigenically well-matched and drifted viruses (Belshe et al., 2007).

Together, the cytoarchitecture and immunological armamentarium of Waldeyer’s ring, particularly the adenoids, constitute an intriguing basis for the current interest in exploiting the nasal route for vaccine administration to combat a variety of diseases (Vajdy and Singh, 2006). The adjuventation and delivery systems of inactivated nasal vaccines should be as tissue-compatible as possible. Many approaches are explored and several have been tested in phase I clinical trials (Jabbal-Gill, 2010). Side effects must be carefully monitored, but nasal vaccine administration seems to be much less risky than pulmonary delivery by aerosol technology (Lu and Hickey, 2007). As noted previously, it remains to be seen if sublingual vaccine administration—with the advantage of being a very safe approach—might become a practical alternative to NALT or pulmonary immunization (Czerkinsky et al., 2011).

CHALLENGE #8

New methods to deliver vaccines.

Despite its relative rusticity, the oldest human vaccine, vaccinia, has been one of the easiest to use. It does not require injections because it is given into the skin, it is rather stable, and it is efficacious after only a single administration. Such properties represent a remarkable advantage for a health tool to be used in the most difficult conditions, and they have probably contributed to the success of smallpox eradication. Although it requires a logistically demanding cold chain and repeated administration, the second easiest vaccine to deliver happens to be the oral polio vaccine, and again this is facilitating a move toward massive global use, which should eventually lead to elimination of the disease.

Vaccine delivery systems are important determinants of the effectiveness of vaccination strategies. In developing countries, there is a considerable comparative advantage for vaccines that would not require injections, and thus avoid the risk of contamination. It is estimated that, in the year 2000, close to one-third of all injections carried out in Africa were not done within the desirable safety standards. Thus, the risk of bacterial contamination or blood-borne disease transmission could not be fully excluded. Syringes that cannot be reused and vaccines that can be given orally, such as OPV, completely avoid the injection-associated risk. They are particularly well-accepted and well-suited for vaccination campaigns. Vaccines that are relatively heat-stable, e.g., DTP, and do not require a strict cold chain system also bear an intrinsic advantage.

It is a real challenge to ensure that the delivery issue be considered for vaccines under development. Some of the new emerging products are of special interest, such as nasal vaccines that use live vectors or subunit formulations with appropriate adjuvants, as well as DNA vaccines that can be administered using the gene gun technology.

CHALLENGE #9

Appropriate vaccines for the elderly, newborns, and adolescents. Vaccination in the context of an increasing prevalence of immunodeficiency.

We have learned a great deal about how to deliver vaccines to young children to protect them against childhood infectious diseases. This has required responding to extraordinary logistical challenges in every country, developing ways of integrating immunization programs into public health and primary care programs, and maintaining a global cold chain to ensure the immunologic integrity, quality, and safety of vaccines. The new challenges will be how to develop comparably responsive immunization systems to reach new populations. One is the elderly, who present immunological challenges at two levels: how to immunize individuals whose immune system is often wearing out, and how to reach them with vaccines. In the United States from 1995 to 1998, it is estimated that 26,000 people over 60 years of age died annually from two vaccine-preventable diseases: influenza and pneumococcal pneumonia [17, 18]. The death or disability of anyone who could have been protected by an existing vaccine is a tragedy. Economic analyses indicate that these vaccines are highly cost-effective, yet even in the United States there is no organized system or program for adult immunization. It will be a challenge to set up immunization for adults as a national priority in most countries. The public health leaders will have to inform and motivate the public and give incentives to healthcare professionals, hospitals, nursing homes, and public health systems to immunize the elderly against the infectious diseases that put them most at risk.

At the other end of the spectrum is the immunological challenge of engendering strong and protective immune responses in newborns. That is a time in which the immune system is not yet fully developed, such that many carbohydrates and even some protein antigens fail to engender adequate protective immunity. We have learned by conjugating carbohydrates to common protein antigens, as in the case of Hib and pneumococcal vaccines, that T cells can be engaged to recognize the protein epitopes so as to provide helper activity that augments the quantity and quality of B-cell responses to carbohydrates. Here is a case in which new “carrier” proteins and new kinds of immunological adjuvants need to be developed. They could augment immune responses in new-borns, decrease the number of booster shots, and decrease the time required to achieve protective levels of immune responses. This will be relevant to any new vaccine in which carbohydrate or lipid antigens are essential targets of immune responses as, for example, in vaccines against streptococcal, staphylococcal, and salmonella infections.

Finally, the HIV–AIDS epidemic, which is increasing dramatically in many developing countries and is the major cause of death among infectious diseases, is paralleled by coepidemics of tuberculosis and hepatitis C. They affect young adults primarily, and these and other sexually transmitted infections require new vaccines and an entirely new vaccine delivery strategy. For adolescents in schools, there is the opportunity to set up school immunization programs. For example, the increase in measles and atypical measles in previously vaccinated young people has led to a revaccination and “booster” program for young teenagers in schools throughout the United States. Yet in developing countries, it is difficult to add further responsibilities to overburdened school systems where teachers are overworked. In many resource-poor countries, a large percentage of young people are not in schools and therefore are difficult to access. New social institutions with the ability to provide reproductive counseling and immunization of adolescents and young people will need to be created. Because of the urgency of the threat of HIV–AIDS, it is essential now to initiate some imaginative experiments on reaching young people in this age group.

Immunization of immunodeficient individuals poses special problems. First is the risk of adverse events, particularly if live attenuated vaccines in immunocompetent individuals are unable to be controlled and cause disease. We know that children suffering from serious immunodeficiency diseases frequently suffer fatal infections from OPV and measles, yet the experience in adults is less clear. Because of the long latency in HIV before the symptoms of AIDS develop, there is the possibility of providing significant levels of protection prior to major immunodeficiency. In several studies of BCG immunization, the incidence of adverse effects in HIV-seropositive children was no greater than in healthy children. Thus, at the first level, the risks from immunization, even from live attenuated vaccines, are not entirely clear.

Second, to ensure safety, it will be advantageous to immunize with either effective subunit vaccines or live attenuated vaccines that have been sufficiently genetically modified to ensure that they cannot cause disease even in immunodeficient individuals. At a third level, even if one can safely vaccinate immunodeficient individuals, there is the question of what the implications would be if the level of immunity falls short of that seen in the general population. How will that affect the transmission and persistence of infections? These are important questions for which we need more information from studies in animal models, from epidemiological analyses of experiences in individuals who were later found to develop immunodeficiency, and from studies in highly endemic populations.

Ultimately, there may be ethical issues raised similar to those raised by the rotavirus vaccine. In this case, although the vaccine provided a major reduction in death from the infection, which kills 800,000 young children worldwide annually, it had a serious adverse effect, intussusception or strangulation of the intestine, in a small number of children. The safety concern required that the vaccine be removed from the market in the United States. The public health argument would be that many more lives could have been saved than the small fraction adversely affected had the vaccine been used in high endemic countries, although the vaccine would have caused some deaths. It is conceivable that there will be effective vaccines that will raise similar ethical concerns due to adverse effects in immunodeficient individuals.

Influenza

Numerous studies have indicated that current parenteral vaccines against influenza are effective in reducing morbidity and mortality associated with infection in the elderly (Nichol et al., 1994; Nordin et al., 2001). Moreover, challenge studies in healthy adults have demonstrated the efficacy of parenteral influenza immunization against infection (Couch et al., 1981), and there is evidence that vaccination of healthy working-age adults may also be cost-effective (Nichol et al., 1995).

While current parenteral influenza vaccines are licensed on the basis of their ability to stimulate serum neutralizing antibodies, experimental studies in humans and animals suggest that mucosal antibody and local cellular responses may also play a role in mediating protection (Renegar and Small, 1991; Powers et al., 1996; Clements et al., 1986). The extent to which parenteral influenza vaccines induce immune responses at the mucosae is unclear. While parenteral immunization with conventional inactivated influenza vaccine has been reported to produce antibody responses in mucosal secretions (Brokstad et al., 1995; Moldoveanu et al., 1995), such antibody may be serum-derived. In this regard, Brokstad et al. (2002) reported that no significant increase in anti-flu antibody-secreting cells was observed in the nasal mucosae of human subjects immunized with the parenteral influenza vaccine.

It should be pointed out that some studies indicate that a combination of parenteral immunization with the current split subunit vaccine, together with a live-attenuated nasal vaccine, may provide better mucosal immune responses than either vaccine, although no determination of correlation with efficacy was undertaken in these studies (Gorse et al., 1996). There appears to be a need to increase the efficacy of influenza vaccination with respect to reducing the incidence of clinical disease associated with influenza (Demicheli et al., 2001). Nasally administered influenza vaccines have matured in recent years, with a live attenuated vaccine reaching the markets and several nasal subunit vaccines in clinical development. Such vaccines have the potential for increased efficacy and ease of use.

Respiratory syncytial virus (RSV)

While a licensed vaccine against RSV has not yet been developed, it is interesting that passive immunization with high-titered RSV immune globulin is effective in preventing RSV disease and infection of the lower respiratory tract in infants (Groothuis et al., 1993). This is not surprising since, as described above, the lower respiratory tract is well endowed with IgG. Additional transudation of antibody from serum early after the infectious challenge might also amplify the role of IgG antibody in neutralizing the virus and preventing its entry and/or replication in the respiratory tract. Passive immunization is believed to be useful in providing protection only for short periods in infants at high risk, such as those about to undergo cardiac surgery or infants born prematurely. These findings suggest that a parenteral vaccine that induces high levels of serum neutralizing antibody should also be sufficient to prevent RSV infection in individuals at risk, such as infants and children and possibly the elderly. As mentioned previously, parenteral immunization may induce local IgA antibody as well as IgG antibody, but it is not clear to what extent secretory IgA (S-IgA) antibodies are required for optimal protection against RSV. In the case of RSV, the choice of parenteral versus mucosal vaccine for infants will also take into account the potential of each to induce enhanced disease following natural infection, as was observed with an experimental vaccine evaluated in the 1960s (Kim et al., 1969).

Cytomegalovirus (CMV)

Postnatal infection of infants and/or mothers with cytomegalovirus is thought to occur via the nasal/oral route. While both cell-mediated and humoral immunity are important for immunity to CMV, efforts to develop a parenteral vaccine have been stimulated by the fact that naturally acquired maternal antibody appears to be protective against damaging congenital infection (Fowler et al., 1992), and passive immunization of renal transplant patients with immune globulin also reduced the severity of disease caused by CMV (Snydman et al., 1990). A study of individuals immunized with either of two candidate vaccines provided further support for the notion that parenteral immunization can generate antibody responses in mucosal secretions. Both live attenuated (Towne strain) and an adjuvanted subunit (gB protein in MF59) candidate vaccine induced antibody responses in mucosal secretions as well as in serum. The greatest responses were observed in individuals who had received two immunizations of the adjuvanted subunit vaccine. The quantity of IgG and IgA antibody measured in parotid saliva and nasal wash correlated positively with the quantity of antibody measured for each respective isotype in serum, suggesting that in this case, transudation from serum to these mucosal secretions could account for the appearance of IgG and IgA antibody following parenteral immunization (Wang et al., 1996). In the case of CMV, parenteral immunization might be expected to prevent disease caused by systemically disseminated virus and possibly by preventing infection at the mucosae. Clinical trials will be required to establish these points.

Rubella

Rubella virus infection is transmitted via the nasopharynx, where it replicates. Approximately 2 weeks following infection, a prolonged viremia develops. Protection against disease is thought to be mediated by serum antibody (Davis et al., 1971; Matter et al., 1997). Following natural infection, reinfection may occur if a seropositive individual is exposed to rubella, its incidence depending on the size of the challenge, the level of serum antibody, and probably the presence of secretory antibody, as discussed below.

Studies of a live attenuated rubella vaccine (strain RA27/3), which is capable of replicating in the nasopharynx, indicated that protective immunity could be induced whether the vaccine was given by the nasal route or by the parenteral route. In these studies, protection was scored by the lack of a secondary antibody response following challenge with wild-type virus (Ogra et al., 1971; Fogel et al., 1978). In contrast, another rubella vaccine (HPV-77) did not prevent reinfection. Analysis of the antibody responses induced by these two vaccines indicated that the RA27/3 strain induced both serum and nasal antibody, while the HPV-77 strain induced only serum antibody (Banatvala et al., 1979). These data suggested that resistance to reinfection correlated, in part, with the presence of mucosal antibody responses, and these could be induced by both parenteral and intranasal administration (Plotkin et al., 1973).