Ebola virus vaccine: Canadian Immunization Guide
For health professionals
New chapter: September 2023
This new chapter was developed based on the following statements:
- March 2023: Ebola Disease Prevention, Monitoring and Surveillance Recommendations from the Committee to Advise on Tropical Medicine and Travel (CATMAT)
- February 2020: Interim Statement on the Use of the rVSVΔGZEBOV-GP Vaccine for the Prevention of Ebola Virus Disease
This information is captured in the table of updates.
On this page
- Key information
- Preparations authorized for use in Canada
- Immunogenicity, efficacy and effectiveness
- Recommendations for use
- Vaccination of specific populations
- Serologic testing
- Administration practices
- Storage requirements
- Safety and adverse events
- Other considerations
- Chapter creation process
- Selected references
- Ebola disease is a rare, severe, acute viral illness caused by viruses within the genus Orthoebolavirus (formerly Ebolavirus). There are four orthoebolaviruses that can cause Ebola disease in humans. Ebola virus (EBOV) (Orthoebolavirus zairense formerly Zaire ebolavirus) causes Ebola virus disease (EVD). EBOV is considered the most virulent of all orthoebolaviruses, having the highest case fatality rate and being responsible for the majority of outbreaks to date.
- EVD usually begins with a sudden onset of flu-like symptoms, such as fever, myalgia, severe headache, and malaise, typically followed by worsening gastrointestinal symptoms and hemorrhaging. The EVD case fatality rate ranges from 25 to 90%.
- Ebola Zaire vaccine, Ervebo® (EZV) is recommended for individuals 18 years of age or older for protection against EVD.
- While Ervebo® is now authorized in Canada, it is not currently available or recommended for Canadians as part of routine immunization or for vaccination prior to travel.
- The vaccine should be offered as post-exposure prophylaxis to persons who have been exposed to EBOV in Canada.
- The provision of vaccination against EVD to Canadian humanitarian workers who travel to EBOV affected areas to provide care to confirmed EVD cases or their contacts or engage in safe burials, is the responsibility of the organization delivering these services.
- EZV is not indicated against the other types of orthoebolaviruses or related filoviruses. Due to their antigenic differences, the vaccine is not expected to provide adequate protection.
- Primary immunization is achieved with one dose of EZV
- Used as post-exposure prophylaxis, EZV should be given within 72 hours of exposure but may be given up to 10 days post-exposure.
- EZV is available via the National Emergency Strategic Stockpile (NESS).
- Vaccination with EZV currently offers the best available protection against EVD.
- EZV has shown few serious adverse events and has been demonstrated to be immunogenic in non-pregnant immunocompetent adults.
- The vaccine has been shown to be efficacious in preventing EVD in community outbreaks.
Ebola disease is a rare, severe, acute viral illness caused by ribonucleic acid viruses within the genus Orthoebolavirus (formerly Ebolavirus) which belongs to the Filoviridae family. Six orthoebolavirus species have been established, of which four contain viruses known to cause human disease: Ebola virus (Orthoebolavirus zairense), Sudan virus (Orthoebolavirus sudanense), Taï Forest virus (Orthoebolavirus taiense) and Bundibugyo virus (Orthoebolavirus bundibugyoense).
Ebola virus disease (EVD) is caused by the EBOV (Orthoebolavirus zairense formerly Zaire ebolavirus), and is considered the most virulent orthoebolavirus, having the highest case fatality rate and being responsible for the majority of outbreaks to date.
For more information about the EBOV, refer to the Pathogen Safety Data Sheet.
The natural reservoir for orthoebolaviruses is not fully understood, but fruit bats are believed to be the natural host of EBOV.
EBOV is transmitted to humans through handling, preparing or ingesting infected animals (for example, bats, wild game), or from person to person via contact with the blood and body fluids (for example, emesis [vomit], urine, stool, sweat, breast milk secretions, saliva, semen), or from tissue of an infected person directly or indirectly through contact with contaminated objects. Infectiousness starts from the time of symptom onset and the risk of transmission is highest when viral load is greatest.
Risk factors and exposure definition
In Canada, the risk of exposure to EBOV is very low. Specific occupational groups like laboratory and health care workers are at higher risk of exposure due to their work particularly if there are breaches in recommended infection prevention and control measures or unprotected blood or body fluid exposures.
Globally, activities associated with a higher risk of exposure to the virus include:
- provision of care to EVD cases who are ill, without proper and consistent use of appropriate personal protective equipment or in the event of blood or body fluid exposure (such as needlestick injuries)
- unprotected sexual contact with an EVD case who is acutely ill, or during their recovery
- pregnancy (from mother to child)
- participation in unsafe burial practices, including the preparation of the deceased for burial
- handling and/or consumption of wild animals hunted or gathered for food (bushmeat) from affected areas
Spectrum of clinical illness
EVD has an incubation period of 2–21 days, with most cases experiencing onset of symptoms around 4–10 days after exposure. Disease usually begins with a sudden onset of flu-like symptoms, such as fever, myalgia, severe headache, and malaise, typically followed by worsening gastrointestinal symptoms and fluid loss. Diarrhea and vomiting can be profuse in later stages of the illness. The disease can progress to severe volume depletion, electrolyte abnormalities, wasting, and shock. Haemorrhage is a late manifestation and, in recent outbreaks, occurs in fewer than half of cases, usually from the gastrointestinal tract or other mucosa. Case fatality in humans ranges from 25–90%.
Following clinical recovery of a patient, EBOV can remain in immunologically privileged body sites where it is protected from the individual's immune system. Immunologically privileged sites include the testes, eyes, placenta, and the central nervous system. Follow-up of a cohort of EVD survivors in Liberia has demonstrated persistence of the virus in semen for up to 40 months with a range of 233 to 1178 days and a median of 551 days. Relapse of viremia can also occur.
Full recovery occurs over a long period of time and can be associated with long-term sequelae such as myelitis, recurrent hepatitis, psychosis and uveitis.
Incidence and prevalence
Sustained chains of transmission of the viruses causing EVD are typically restricted to areas of sub-Saharan Africa, with epidemic disease occurring in parts of Central Africa, West Africa and East Africa. While possible, the risk of EVD transmission outside of an outbreak area, by travellers is very low. More recent outbreaks have had significantly altered epidemiology due to the use of EVD vaccines for healthcare workers and close contacts of EBOV-infected patients. EVD is a nationally and internationally notifiable disease.
Information about countries with risk of EBOV transmission and countries requiring EBOV vaccination is available through the World Health Organization. Outbreaks are reported in the WHO Outbreak News.
Preparation authorized for use in Canada
In Canada, EZV is available through the National Emergency Strategic Stockpile (NESS) for the management of exposures to cases detected in Canada and management of potential outbreaks. Access to the vaccine and information on who is eligible to receive EZV for management of exposures or outbreaks within Canada would be determined in consultation with the relevant public health authorities. The provision of vaccination against EVD to Canadians travelling for international aid work remains the responsibility of the organization delivering services. Individuals travelling to EVD-affected areas through humanitarian organizations should enquire with their host organization about the availability of EBOV vaccination.
Ebola Zaire vaccine
- ERVEBO®: live, attenuated, Ebola Zaire vaccine, Merck Canada Inc. (EZV)
The EZV vaccine is a live-attenuated, recombinant vesicular stomatitis virus (rVSV)-based vaccine against Ebola virus. The vaccine contains a gene for the Ebola virus glycoprotein that replaces the gene for the native rVSV glycoprotein. This vaccine is not indicated for use against the other orthoebolaviruses, such as Sudan virus or Bundibugyo virus, or related filoviruses, such as Marburg virus.
Preparations authorized for use in Canada may not be currently available for sale. Refer to Health Canada’s Drug Product Database (DPD) for its drug status. Definitions of drug status can be found under DPD Terminology.
For complete prescribing information, consult the product leaflet or information contained within Health Canada's authorized product monograph available through the Drug Product Database.
Refer to Table 1 in Contents of immunizing agents authorized for use in Canada in Part 1 for a list of all vaccines authorized for use in Canada and their contents.
Immunogenicity, efficacy and effectiveness
It is important to note that no immunological correlate of protection has been established for EVD, so it is difficult to interpret immunogenicity findings in the context of disease prevention. Studies assessing antibody responses to EZV showed that vaccine recipients had developed EBOV glycoprotein-specific immunoglobulin G (IgG) and neutralizing antibodies that peak at 1 month and may persist for 1 to 2 years post-immunization. However, the data on antibody persistence is limited and its interpretation has been mixed.
Efficacy and effectiveness
Vaccine protection was only assessed in the context of outbreak settings (ring vaccination) and post-exposure prophylaxis of laboratory and healthcare workers with all showing nearly 100% effectiveness. Uncertainties remain regarding the level, duration and type of protection given the limitations of available evidence.
Recommendations for use
Children and adolescents
A single dose of EZV may be considered for use in infants, children and adolescents who have been exposed to EBOV in Canada.
Refer to Post-exposure immunization for more information.
A single dose of EZV is recommended for non-pregnant and immunocompetent individuals following exposure to EBOV in Canada. EZV may also be considered for use in immunocompromised individuals or pregnant individuals following occupational exposure in laboratory or healthcare settings in Canada. EZV may also be used for pre-exposure immunization in certain circumstances.
Pre-exposure prophylaxis against EVD may be considered for non-pregnant and immunocompetent adults in exceptional situations when a dedicated team of healthcare workers is anticipated to provide direct care for a person with confirmed, symptomatic EVD.
EZV should be given as expeditiously as possible, targeting within 72 hours of exposure for susceptible, asymptomatic exposed individuals but may be considered up to 10 days post-exposure, as the incubation period can range from 2 to 21 days and vaccination within 10 days of exposure may confer protection. For previously immunized individuals, EZV may be considered if the vaccine was received more than 18 months prior to the current exposure.
Booster doses and re-immunization
Studies are underway to determine the need to offer a booster dose and an appropriate interval for booster dosing. Expert clinical opinion should be sought when deciding whether to re-vaccinate an individual who has previously received another vaccine for EBOV.
Vaccination of specific populations
Pregnancy and breastfeeding
There are limited safety data from the use of EZV in pregnant and breastfeeding people, or in people who became pregnant after receiving the vaccine. The safety of EZV has not been established in pregnant or breastfeeding people. Nevertheless, given the seriousness of EVD, the vaccine may be considered for pregnant individuals who have had an exposure to EBOV, occupational or otherwise, in Canada.
Pregnancy should be avoided for 2 months following vaccination. Women of child-bearing potential should use an effective contraceptive method.
Refer to Vaccine virus shedding for information regarding precautions related to breastfeeding following EZV vaccination. Refer to Immunization in pregnancy and breastfeeding in Part 3 for additional general information.
There are limited data on safety and efficacy of EZV in immunocompromised individuals. However, EZV may be considered as postexposure prophylaxis following exposure, occupational or otherwise, to EBOV in Canada. In other circumstances, as a precautionary measure, the use of EZV should be avoided in individuals with known immunocompromised conditions or who are receiving immunosuppressive therapy.
Refer to Immunization of immunocompromised persons in Part 3 for additional information.
The vaccine may be offered to some humanitarian workers deploying to an EVD-affected area (such as, to those that may provide care to confirmed EVD cases or their contacts, including contacts of a deceased case), or to those that may be engaged in safe burials, and to other healthcare or frontline workers in affected areas and areas at high risk of spread.
For other travellers, even in endemic EBOV areas, EBOV poses negligible risk. A greater risk exists for travellers who meet the exposure definition. EZV is not currently available or recommended for Canadians as part of routine immunizations or vaccinations prior to travel. Individuals travelling to EVD-affected areas through humanitarian organizations should enquire with their host organization about the availability of EZV.
For more information on EBOV and travellers, refer to the Committee to Advise on Tropical Medicine and Travel’s, Ebola disease prevention, monitoring and surveillance recommendations. Refer to Immunization of Travellers in Part 3 for additional general information.
EZV may be considered as pre-exposure prophylaxis against EBOV for non-pregnant, immunocompetent adults in exceptional situations when a dedicated team of healthcare workers is anticipated to provide direct care for a confirmed case with symptomatic EBOV infection, if vaccine is available.
EZV should be offered as post-exposure prophylaxis against EBOV for non-pregnant, immunocompetent adults who have had an occupational exposure in Canadian healthcare or laboratory settings; and EZV may also be considered as post-exposure prophylaxis for pregnant or immunocompromised individuals who have had an occupational exposure to EBOV in Canadian healthcare or laboratory settings.
Serologic testing is not recommended before or after receiving EZV Vaccine.
Dose and route of administration
Each dose is 1 mL. EZV vaccine should be administered intramuscularly.
Refer to Vaccine administration practices in Part 1 for additional information.
Concurrent administration with other vaccines
There are no data on concurrent administration of EZV with other vaccines. The vaccine should not be given concurrently with other live or inactivated vaccines due to the potential for immune interference and the need to be able to monitor for potential symptoms of EVD and EZV adverse events without potential confounding from other vaccine adverse events.
Vaccination with EZV does not eliminate the need for healthcare workers to adhere to strict precautions with regards to the use of personal protective equipment in caring for patients with suspected or confirmed EBOV infection.
EZV is stored frozen at -80°C to -60°C and should be removed from the freezer and thawed in less than 4 hours until no visible ice is present. For complete information on storage, handling and disposal, consult the Health Canada authorized product monograph available through the Drug Product Database.
Refer to Storage and handling of immunizing agents in Part 1 for additional general information.
Safety and adverse events
Common and very common adverse events
The most frequently reported adverse events were injection site pain (69.6%), fever (23.2%), headache (22.3%), malaise, and myalgia. These adverse events were generally transient and mild-to-moderate in intensity. The onset of systemic symptoms typically occurred within three days after vaccination.
Several studies found arthralgia and arthritis of mild to moderate intensity were reported at a low frequency, and usually resolved within 6 days of onset. Non-vesicular rash and vasculitis, mild-to-moderate in intensity, and of short duration were also reported. A small proportion of vaccine recipients may develop a vesicular rash. These vesicles should be covered until healed to minimize the possibility of vaccine virus transmission to other humans or animals.
Uncommon, rare and very rare adverse events
Serious adverse events were infrequently reported and included fever and anaphylaxis. The probability of detection of very rare adverse events in clinical trials and early follow up studies is low given sample sizes; therefore, ongoing pharmacovigilance is essential.
Other safety issues
Transient, asymptomatic, decreases in leukocytes were seen in some vaccine recipients within 2 days post-vaccination.
Guidance on reporting Adverse Events Following Immunization (AEFI)
To ensure the ongoing safety of vaccines in Canada, reporting of AEFIs by vaccine providers and other clinicians is critical, and in some jurisdictions, reporting is mandatory under the law.
Vaccine providers are asked to report AEFIs through local public health officials and to check for specific AEFI reporting requirements in their province or territory. In general, any serious or unexpected adverse event felt to be temporally related to vaccination should be reported.
Refer to Vaccine safety and pharmacovigilance and Adverse events following immunization (AEFI) in Part 2 for additional information on vaccine safety and for definitions of AEFIs, and reporting of AEFI to public health.
Contraindications and precautions
EZV is contraindicated in patients who are hypersensitive to this vaccine or to any ingredient in the formulation, including any non-medicinal ingredient, rice protein, or component of the container.
Vaccination should be postponed in subjects experiencing moderate or severe febrile illness. The presence of a minor infection should not result in deferral of vaccination. Vaccine recipients should avoid donating blood for 6 weeks post-immunization.
Vaccine virus shedding
Transmission of rVSV has not been reported to date, but studies have shown some vaccine recipients had measurable shedding of rVSV in urine and saliva. Low-level transient rVSV viremia that has been observed in some vaccine recipients has not been detected at more than 14 days post immunization.
Although the risk of transmitting the EZV virus from person-to-person appears to be extremely low, vaccine recipients should be informed that EZV is comprised of a live, attenuated recombinant virus, rVSV, that has the theoretical potential to be transmitted to contacts of the vaccinated individual.
As a precaution, individuals vaccinated with EZV should avoid close contact, including exposure to blood and body fluids, with immunocompromised individuals, pregnant or breastfeeding women, and infants for at least six weeks following vaccination, unless those individuals also have an indication for EZV.
It is not known if the vaccine virus is secreted in human breast milk and there is no data available regarding the effects of vaccinating breastfeeding women on their infants. As a precaution, women should avoid breastfeeding, and their infants should not have contact with maternal blood and body fluids, where feasible, for at least six weeks following vaccination, unless vaccination with EZV is also indicated for the infant.
Transmission of the vaccine virus to livestock through close contact is a theoretical possibility. Vaccine recipients should try to avoid exposing livestock to their blood or body fluids for 6 weeks post-immunization.
Vaccine recipients who develop a vesicular rash should cover vesicles until healed to minimize the possibility of vaccine virus transmission to other humans or animals. Contaminated bandages should be disposed of properly.
For more additional general information, refer to Contraindications and precautions in Part 2.
No drug interaction studies have been performed.
Blood products, human immunoglobulin and timing of immunization
As EZV is a live, attenuated vaccine, immune globulin (IG), blood or plasma transfusions should not be given concurrently with EZV. Administration of immune globulins, blood or plasma transfusions administered 3 months before or up to 1 month after EZV administration may interfere with the expected immune response. Refer to Blood Products, Human Immunoglobulin and Timing of Immunizationin Part 1 for additional information.
Monoclonal antibody treatments designed to treat EVD have a high affinity for the EBOV glycoprotein, which is expressed by both EBOV and the vaccine vector, and they inhibit EBOV infection by inactivating the virus glycoprotein. The potential for monoclonal antibody treatments that target the EBOV glycoprotein to interfere with EZV is unknown, but administration of monoclonal antibody treatments concurrent with the administration of EZV may in theory result in decreased effectiveness of EZV and/or the monoclonal antibody treatment because the monoclonal antibodies may inactivate the vaccine virus before the body has had time to elicit a protective immune response. In the post-exposure setting, expert clinical opinion should be sought when deciding whether monoclonal antibody treatment, EZV, or a combination of the two is the most appropriate response, taking into account the specifics of the exposure event.
Chapter creation process
This new chapter was developed based on the Interim Statement on the Use of the rVSVΔGZEBOV-GP Vaccine for the Prevention of Ebola Virus Disease from the National Advisory Committee on Immunization (NACI). In addition, it incorporates key information from the Committee to Advise on Tropical Medicine and Travel’s statement on Ebola disease prevention, monitoring and surveillance recommendations.
This chapter was prepared by S Pierre and F Crane and reviewed by C Jensen, O Baclic, A Killikelly, L Banadyga and R Harrison. We acknowledge the work of the NACI EVD Working Group which developed the NACI statement upon which the chapter is based: Y-G Bui, M Libman, S Vaughan, R Harrison, S Deeks, C Quach; along with the Statement authors: L Zhao, A Killikelly, M Tunis, M Patel, G Poliquin, S Deeks and C Quach.
Committee to Advise on Tropical Medicine and Travel. Statement for travellers and yellow fever. Ebola Disease Prevention, Monitoring and Surveillance Recommendations. Ottawa: Public Health Agency of Canada; March 17, 2023. https://www.canada.ca/en/public-health/services/catmat/ebola-virus-disease-preventive-measures-monitoring-surveillance-travellers.html
Biedenkopf, N., Bukreyev, A., Chandran, K. et al. Renaming of genera Ebolavirus and Marburgvirus to Orthoebolavirus and Orthomarburgvirus, respectively, and introduction of binomial species names within family Filoviridae. Arch Virol 168, 220 (2023). https://doi.org/10.1007/s00705-023-05834-2
Ebolaviruses: Infectious substances Pathogen Safety Data Sheet. Ottawa: Public Health Agency of Canada; March 2, 2023. https://www.canada.ca/en/public-health/services/laboratory-biosafety-biosecurity/pathogen-safety-data-sheets-risk-assessment/ebolavirus.html
Merck Canada Inc. Product Monograph - ERVEBO®. November 9, 2022. https://pdf.hres.ca/dpd_pm/00068254.PDF
National Advisory Committee on Immunization. Interim Statement on the Use of the rVSVΔG-ZEBOV-GP Vaccine for the Prevention of Ebola Virus Disease. February 2020. https://www.canada.ca/en/public-health/services/publications/vaccines-immunization/interim-statement-vaccine-prevention-ebola-virus-disease.html
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