Release date:2023/1/17 17:19:45

Nasal spray vaccines are a promising route of vaccination and offer unique advantages, especially in the prevention of infectious diseases transmitted via the respiratory tract. Compared to injectable vaccines, nasal spray vaccines also have the advantage of being less invasive and easier to store and distribute.


The nasal spray vaccine for influenza has been used stably for more than a decade, and the first nasal spray COVID-19 vaccine has been approved for emergency use in China and India. Here, we focus on the influencing factors and current status of the nasal spray vaccine development.

Physiological Structure and Immunogenicity of the Nasal Cavity

The nasal cavity refers to the interior of the nose or the structure that opens exteriorly at the nostrils. It is the entrance to the inhaled air and is the first of a series of structures that make up the respiratory system. The nasal cavity is completely lined by the nasal mucosa, one of the anatomical structures that form the physical barrier to the body's immune system. These barriers provide mechanical protection against the invasion of infectious and allergic pathogens.


Vaccines are also foreign antigens, and the nasal cavity activates immune mechanisms when exposed to foreign antigens (vaccines). Upon entering the nasal cavity, the antigen is trapped on the mucosal epithelium and the microfold cells (M cells) of the lymphoid follicular epithelium then absorb the antigen particles. Subsequently, the antigen is moved to the basal end of the cell and passed on to antigen-presenting cells (APCs), such as dendritic cells (DCs) and macrophages. Thereafter, DC cells migrate through afferent lymphatic vessels to nearby draining lymph nodes where antigen is presented to naive T and B cells via the MHC-II complex.

Nasal-associated lymphoid tissues (NALTs) are an important component of mucosal immunity in the respiratory tract. nALTs have a high distribution of M cells and are the main site of uptake of macromolecular drugs and particles in the nasal cavity, as well as the main site of antigen delivery in the nasal immune response. NALTs have antigen-specific effector B and T cells that differentiate into plasma cells that produce aggregated IgA and IgG and eventually differentiate into sIgA, triggering an immune response that intercepts antigens and pathogens. Mucosal immunity also has a unique set of mechanisms for co-immunity that induces an immune response in distal mucosa, such as the digestive and genital tract mucosa, but usually the intestinal immunity activated by nasal spray vaccines is less effective.

Similar to nasal administration, nasal spray vaccines need to overcome multiple constraints, such as the effect of nasal mucosal cilia clearance, the problem of short residence time in the nasal cavity, and the obstruction of antigens by the mucus and epithelial layers of the nasal mucosal site. The solution of these problems often also requires the assistance of immune adjuvants and penetration enhancers.

Key Technical Factors in the Development of Nasal Spray Vaccines

Most of the currently marketed nasal vaccines are live attenuated influenza virus vaccines. We now present several key factors that should be considered when researching and developing nasal spray vaccines, mainly from the perspective of the immune process.

1. First Step of Drug Delivery - Dosage Forms and Delivery Equipment

Successful nasal delivery first requires the cooperation of a suitable device. Although the nasal cavity has a large mucosal surface area, intranasal delivery of vaccines is limited by nasal anatomy and aerodynamics, where drugs with large particle sizes are usually deposited in the anterior nose and consequently expelled or wiped off, while small particle sizes (i.e., <10 μm) may bypass the nose and enter the lungs. Thus, a suitable device is needed to disperse the intranasal vaccine formulation into appropriate particle sizes for delivery to the posterior region of the nose, and achieving a balance of particle sizes is critical to increasing antigen exposure to the nasal mucosa. FluMist vaccines currently is delivered using the AccuSpray nasal delivery system. In addition, MAD Nasal from Teleflex, ViaNase from Kurve, PuffHaler from Aktiv-Dry, and Solovent from BD all offer nasal mucosal nebulization solutions.

To date, all approved nasal spray vaccines have been in liquid form because of the high solubility and potency of liquid vaccines. However, liquid formulations are fluid and any liquid that exceeds the nasal volume will be drained from the nasal cavity, and only highly soluble or low dose antigens can be delivered intranasally via liquid formulations. The application of dry powder formulations, on the other hand, requires a prolonged residence time in conjunction with mucoadhesive polymers such as starch and chitosan to improve antigen availability to the nasal lymphatic tissue.

2. Prolonging The Residence Time Of Vaccine – Mucoadhesives 

Mucoadhesives are commonly used in the development of nasal spray vaccines. Once the mucoadhesive agent in the vaccine comes into contact with the mucus of the nasal epithelium, the polymer hydrates, swells and binds to the mucus, prolonging the residence time of the vaccine in the nasal mucosa. In addition, mucoadhesives also temporarily slow mucus cilia clearance and do not inhibit antigen release from the vaccine. Commonly used mucoadhesive polymers include e.g. chitosan, starch, etc.

3. Promoting Transmembrane Penetration of Vaccines - Permeation Enhancers 

The nasal epithelial layer is covered by a layer of mucus, and nasal spray vaccines/antigens need to complete the penetration of the mucus layer and epithelial cells. Firstly, it is necessary to penetrate the mucus layer. Polyethylene glycol (PEG) can be used as a mucus layer penetration enhancer, while mannitol can dilute the mucus. Therefore, the use of PEG, mannitol or other mucus penetration enhancers in the formulation can help improve the penetration of vaccines/antigens into the mucus layer.

The transport of antigen across the epithelial cell barrier is a critical step in the induction of immunity. Antigens can penetrate the epithelial layer through cells or across cells, and permeation enhancers such as chitosan and bacterial toxins are often used in this process to increase the permeability of antigens to the mucosa. Both chitosan and bacterial toxins can disrupt epithelial junctions and enhance paracellular motility. Specifically, chitosan promotes transcellular uptake of antigens by M cells in the nasal mucosa and intestinal mucosa. In contrast, enterotoxins disrupt the mucosal epithelium and enhance antigen uptake by DC cells, leading to upregulation of CXCR4 and CCR7, thereby allowing DC cells to migrate to lymph nodes.

4. Reducing Potential Intracranial Transport – Nose-to-Brain Transport Inhibitors

An important safety concern regarding nasal spray vaccines is the potential for transport of vaccine antigens or adjuvants from the olfactory epithelium to the central nervous system (CNS), although researchers analyzing 460 adverse events associated with FluMist found only one case of encephalitis and laboratory confirmation that it was caused by an enterovirus. However, the nasal mucosa provides a direct entry point between the external environment and the central nervous system ( nose-to-brain pathway), and compounds can enter the cerebrospinal fluid through the nerves associated with the olfactory area. Therefore, neurophilicity needs to be evaluated in nasal spray vaccine development.

5. Enhancing the Immunogenicity of Antigens - Vaccine Adjuvants

Adjuvants that target APC antigens in the process of immunization can be useful as immunostimulants. Commonly used immune adjuvants are insoluble aluminum salts and TLR agonists.

Insoluble aluminum salts are classical FDA-approved immune adjuvants. Several aluminum salts are currently used in vaccines approved in the United States, such as Alhydrogel (aluminum hydroxide), Adju-Phos (aluminum phosphate), and amorphous aluminum phosphate sulfate (AAPS). The immunostimulatory effects of aluminum salts arise from a variety of mechanisms, including slowing the spread of antigen from the site of administration, increasing inflammatory cell accumulation, activating complement, and inducing the differentiation of monocytes into DCs as well as uptake of antigen, antigen delivery, and activation of CD4+ T cells by DCs.

TLR agonists can act as adjuvants for mucosal immunity; specifically, TLR agonists function as pathogen-associated molecular patterns (PAMPs) and act by binding to pathogen recognition receptors (PRRs) on DC cells. Commonly used are TLR2/6 agonists, TLR3 agonists, TLR3 agonists.

Current Development Status of Nasal Spray Vaccine

1. Approved Nasal Spray Vaccines

FluMist® (MedImmune, LLC) is the first live attenuated influenza virus intranasal vaccine that was successfully approved and commercialized in the US and Europe (as Fluenz®).  It is a vaccine that is sprayed into the nose to help protect against influenza. It can be used in people 2 through 49 years old. 

Nasovac-S is a live attenuated nasal spray vaccine produced by the Serum Institute of India for the prevention of influenza A (H1N1).

The main nasal spray vaccines currently undergoing clinical trials include influenza vaccines (H5N1, H1N1, etc.), human parainfluenza (types 2 and 3), respiratory syncytial virus (RSV), streptococcus pneumoniae, and mycobacterium tuberculosis. Research is also underway on nasal spray vaccines against gonorrhea and chlamydia using antigens from one specific mucosal region to initiate common mucosal immune system properties that can induce responses in different mucosal regions.

2. Safety and Weak Immunogenicity of Nasal Spray Vaccines

Intranasal influenza vaccines are generally considered safe and effective, but there have been examples of withdrawals due to associated adverse events, with the withdrawal of Nasalglu produced by Berna Biotech in 2001 due to induced Bell's palsy. There is also evidence that live attenuated influenza vaccines (LAIVs) can cause encephalitis through the olfactory nerve into the brain (nasal-to-brain pathway). Although these are theoretically sound studies, they should not be ignored in practice.

More important to note, however, is the immunogenicity of nasal spray vaccines. Although the ability of the nasal spray vaccine to induce systemic and mucosal immunity would theoretically lead to greater protective immunity, the efficacy of the nasal spray vaccine would be limited by the short residence time in the nose and the movement of enzymes, mucus, and nasal hairs in the nasal cavity.


Nasal spray vaccines offer many advantages such as ease of administration and the potential to induce systemic and mucosal immunity, which has great potential especially in today's epidemic of respiratory infectious diseases. However, nasal spray vaccines are a multidisciplinary field that integrates formulation, device, and clinical research, and the challenges of developing a new nasal spray vaccine are numerous.

Biopharma PEG is a leading supplier of high-quality PEG derivatives. We can provide PEG derivatives from lab to large scale in GMP and non-GMP grade. PEG derivatives not listed in our catalog can be provided by custom synthesis. 

[1] Alu A, Chen L, Lei H, et al. Intranasal COVID-19 vaccines: From bench to bed.[J]. EBioMedicine, 2022,76:103841.
[2] Lobaina Mato Y. Nasal route for vaccine and drug delivery: Features and current opportunities.[J]. International journal of pharmaceutics, 2019,572:118813.

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