Vaccine Development Process Map

Prioritisation of Vaccine Development decision making guide

This guide is split into three sections, Technical feasibility, Public health value and Time scale and cost of Development. To guide you there are criterion under each main heading which are split into how feasible or how much of a priority that criterion is. Each is coded red for low, yellow for medium and green for high feasibility/priority.

To see how this guide was applied to current vaccines select one of the pathogens below to show selections made.

More information and notes can be found by selecting the notepen notepen icon.

Coxiella burnetii

Technical feasibility

Provenance of pathogen

Coxiella burnetii is the causative agent of Q fever. The primary reservoirs are ruminants such as cattle, sheep and goats. Infections in humans is often asymptomatic but acute or chronic disease can occur. In pregnant women the disease can cause still births, abortions and premature births. Human infection is mostly through the aerosol route, via the inhalation of soils contaminated with fluids from an infected animal. Epidemiology and disease presentation are described. In this category, vaccine production against this organism should be considered highly feasible.

Similarity to known pathogen

Coxiella burnetii is a Gram negative obligate intracellular pathogen. It belongs to the γ subdivision of the proteobacteria. It is a member of the Rickettsiae family including Ehrlichia and Rickettsiae and Orientia, found in ticks, lice, fleas, mites and mammals and all are considered potential zoonotic pathogens.

Can the pathogen be cultured in a laboratory

Coxiella burnetii has been considered difficult to culture for several years due to an absolute requirement for growth within eukaryotic cells. This has significantly hampered the development of genetic tools for manipulating the organism. However, a medium that supports axenic growth has recently been developed, making laboratory culture of this bacterium more amenable. Medium/High feasibility.

Complexity and size of pathogen

The genome of Coxiella burnetii is about 2.2 Mb containing approximately 2,400 genes. This genome size is relatively small when compared to other bacterial genomes sequenced to date.

Antigenic diversity

To score as highly feasible. The organism should have little genetic diversity with low mutation rate. Alternatively, large amounts of genomic data should be available.

Studies indicate that there is a lack of broad genetic variance in Coxiella burnetii. This fits with the organism’s obligate intracellular lifestyle that limits opportunities for genetic exchange. It seems that the organism is in fact undergoing reductive evolution and undergoing genome downsizing to potentially further specialise for its intracellular lifestyle. Several Coxiella burnetii genome sequences are available although the first sequence from a human isolated strain was only published in 2015.

In this category a Coxiella burnetii vaccine scores as highly feasible.

Biomarkers for safety/efficacy

Several human vaccine trials have been carried out against Coxiella burnetii, therefore markers for vaccine safety and efficacy are established. In addition, studies have been published reporting that antibody responses have been characterised in vaccinated as well as acute and chronic Q fever sufferers.

Host-immune response

In order for a vaccine to be assembled against a particular organism, there should be reported cases of natural immunity that is both protective and durable. The pathogen must not be immunomodulatory and neutralising antibodies must be protective.

Coxiella burnetii infection in humans causes Q fever, this is typified by symptoms such as pneumonia, fever, headache and myalgia. In most cases patients recover and are immune to further infections by Coxiella burnetii. B cells have been demonstrated to play a critical role in vaccine-induced immunity to Coxiella burnetii by producing protective antibodies. The exact mechanism however, of protective immunity to Coxiella burnetii is not well understood. Overall a vaccine to prevent Q fever can be rated as Highly feasible based on these findings.

Available model organisms, including human challenge models

Several animal models for Coxiella burnetii infection have been utilised ranging from mice to non-human primates to both evaluate and characterise the organism and vaccines.

Criterion Low feasibility Medium feasibility High feasibility
Provenance of pathogen No understanding of provenance Some understanding of provenance, with limited understanding of epidemiology Known disease, with well understood epidemiology notepen
Similarity to known pathogen Dissimilar, at least in initial analysis, to any known pathogen From a known family of pathogens Closely related to a well characterized pathogen notepen
Can the pathogen be cultured in a laboratory Very difficult to culture Possible to culture, but lengthy and difficult process notepen Can be cultured
Complexity and size of pathogen Large and complex pathogen Medium sized pathogen Small and simple pathogen notepen
Antigenic  diversity High genetic diversity, with high mutation rate and lack of annotated genomic data Some genetic diversity with moderate mutation rate Little genetic diversity, with low mutation rate. Large amounts of well annotated genomic data available notepen
Biomarkers for safety/efficacy No understanding of biomarkers for safety or efficacy Some understanding of biomarkers that may relate to safety/efficacy Clear understanding of biomarkers for both safety and efficacy notepen
Host-immune response No known cases of natural immunity, and pathogen is immune modulatory Some cases of natural immunity, but unclear whether this is durable and protective. Pathogen is generally perceived as not being immune modulatory Cases of natural immunity which are both durable and protective, pathogen is not immune modulatory, and neutralising antibodies are protective notepen
Available model organisms, including human challenge models Lack of suitable animal model, and/or suitable human challenge model  Suitable animal model and/or suitable human challenge model may require some development Suitable animal model, and/or suitable human challenge model is available  notepen

Public health value

Infectivity or rate of spread of pathogen

For a pathogen to be considered high priority in this category it should be poorly transmitted with very slow rate of spread and low attack rate.

The largest ever reported outbreak of Q fever occurred in the Netherlands between 2007-2010 and resulted in more than 3,500 Q fever cases. It should be noted that this organism is considered a zoonotic pathogen with global distribution. Combine this with the high potential for aerosol spread due to the very low infectious dose (10 or fewer organisms) required to potentially cause illness. Reports of high attack rates have been published so the organism could be considered low priority.

In this category notice that under low priority are organisms that have rapid spread and attack rates, one must point out that this is indicated with the caveat that such organisms should be considered low priority unless there is potential to prevent a pandemic by vaccinating populations outside of the affected country. Potential Q fever pandemics could be prevented by such means, therefore the pathogen should actually be classified as high priority.

Case fatality rate/disability burden

Q fever presents itself as a flu-like illness. At times pneumonia and hepatitis can present. A minority of patients are unable to clear the bacteria and develop a chronic infection that often presents as endocarditis (60-70% of chronic infections). The CDC estimates that the rate of hospitalisation among Q fever cases is around 50%. The estimated case fatality rate is less than 2 % of hospitalised patients. Chronic Q fever occurs in about 5% of acutely infected patients and the case fatality rate in untreated patients with endocartidis ranges from 25-60%. Patients with endocariditis require at least 18 months of antibiotic treatment for a successful outcome.

10 to 25% of acutely infected patients suffer from post-Q fever fatigue syndrome. This is characterised by pain in muscles and joints, severe headaches, night sweats and fatigue.

In this category Coxiella burnetii vaccine development should be considered as medium priority.

Infectivity before symptom onset

Person to person transmission of Coxiella burnetii is very rare. In fact this appears as controversial. Developing a vaccine to prevent Q fever should be considered as low priority. However, the risk of infection with this pathogen is not from person to person transmission but from infected animals. Considering this caveat, one should re-categorise the need to develop a vaccine as high priority.

Incubation period:

Incubation periods between 2-3 weeks are routinely reported for acute Q fever.

Chronic infection however may manifest between 6 weeks and several years subsequent to acute Q fever.

Due to this wide range of incubation periods, Coxiella burnetii could be categorised as medium/high priority.

Environmental factors

These cannot be modulated in the case of Coxiella burnetii and as such vaccine development should be considered as high priority.

Geographical spread

Coxiella burnetii is a globally distributed zoonotic pathogen and clearly there is potential for a large disseminated outbreak.

Target population

Coxiella burnetii is considered a potential biological warfare agent. The low aerosol infectious dose and varied animal reservoir does indicate that there is potential for infection irrespective of gender/age/health status. Based on these indication, a Coxiella burnetii vaccine should be considered as high priority. Under normal conditions, the most at risk populations is composed of those individuals who have regular contact with cattle, sheep, maintaining livestock, working in abattoirs or in rural areas.

Availability of potential alternatives to vaccination

Doxycycline is the treatment of choice for acute Q fever. Usual dosage indicated is 100 mg taken orally twice daily for 15-21 days. Chronic Q fever is much more difficult to treat and the recommended treatment is a combination of doxycycline and quinolone antibiotics often prescribed for years. Recently, doxycycline resistant clinical isolates have been described, and independent studies have described DNA gyrase mutants that render strains resistant to quinolones. As such vaccine development should be considered as high priority.

Criterion Low priority Medium priority High priority
Infectivity or rate of spread of pathogen notepen Rapid spread with high attack rate Moderate rate of spread and attack rate Pathogen is poorly transmitted, spread is very slow, and attack rate is low
Case fatality rate/disability burden Low case fatality rate/ disability burden Moderate case fatality rate/disability burden notepen High case fatality rate/disability burden
Infectivity before symptom onset Not infectious before the onset of symptoms May be infectious before the onset of disease Highly infectious before disease onset notepen
Environmental factors Environmental factors are easily modulated Moderately difficult to address environmental factors Environmental factors cannot be modulated notepen
Geographical spread Small isolated pockets of disease Moderately spread Large disseminated disease outbreak notepen
Target population Lack of clarity on target population, with the level of prevention that is acceptable/desirable unclear Some clarity on target population and level of prevention desirable Clarity on target population and level of prevention desirable notepen
Availability of potential  alternatives to vaccination There are good alternatives to vaccination currently available which can be rapidly deployed to control the disease outbreak Effective alternatives to vaccination could be rapidly developed Effective alternatives to vaccination are not currently available and are not on the horizon notepen

Time scale and cost of development

Available vaccine candidate(s)

There is no globally approved vaccine against Coxiella burnetii.

Criterion Low priority Medium priority High priority
Available vaccine candidate(s) No vaccine in development and route map for getting to Phase I trials not yet developed Promising candidates exist, and means of rapidly developing to Phase I can be identified Suitable vaccine may be in late stages of development notepen