CPHA Canvax

COVID-19 Vaccine Questions and Answers for Healthcare Providers

Sonali Kochhar, MD1,  Eve Dubé, PhD2, Janice Graham, PhD3, Youngmee Jee MD, PhD4, Ziad A. Memish, MD5, Lisa Menning6, Hanna Nohynek, MD, PhD7,  Daniel Salmon, PhD8; Karina Top, MD, MS9, Noni E MacDonald, MD10

Affiliations and Conflict of Interest (COI)

  1. Clinical Associate Professor, Department of Global Health, University of Washington, Seattle; Medical Director, Global Healthcare Consulting
    COI - Nothing to declare

  2. Senior researcher at Quebec National Institute of Public Health; Invited Professor in Anthropology, Laval University, Canada
    COI - Nothing to declare

  3. University Research Professor and Professor of Pediatrics (Infectious Diseases) and Anthropology, Dalhousie University, Canada
    COI - Nothing to declare

  4. Visiting Professor, GSPA, Seoul National University; Special Representative for Health Diplomacy, Korea Foundation
    COI - Nothing to declare

  5. Senior Infectious Disease Consultant, Director Research and Innovation Center, King Saud Medical City, Ministry of Health, Riyadh, Saudi Arabia
    COI- Nothing to declare

  6. Technical Officer, WHO HQ Department of Immunization, Vaccines, and Biologicals, Geneva
    COI - Nothing to declare

  7. Chief Physician, Deputy Head of Unit, Finnish Institute for Health and Welfare THL, Finland
    COI - My institute THL has got a strategy of public private partnership; neither myself nor my unit receives such private funds/grants.

  8. Director and Professor, Institute for Vaccine Safety, Johns Hopkins University School of Public Health, United States
    COI - Consulting and/or grants with Merck, Jenssen and Walgreens.

  9. Associate Professor of Pediatrics and Community Health & Epidemiology, Dalhousie University, Canada
    COI - In the past 3 years I have received consultancy fees from Pfizer and grants from GSK to my institution for projects unrelated to this work.

  10. Professor Paediatrics, Dalhousie University, IWK Health Centre, Canada
    COI- Nothing to declare

The CONSIDER Working Group 

In recognition of the critical importance of COVID-19 vaccines and the need to understand their safety, the CONSIDER (COvid-19 vacciNe Safety questIons anD hEalthcare pRoviders) Working Group (WG) was created in September 2020.

The CONSIDER WG aims to provide clear, comprehensive answers to questions pertaining to COVID-19 vaccine safety prior to, and during the vaccines roll out to
1) facilitate scientific discussion between stakeholders, including front line health workers with potential vaccine recipients and
2) increase comprehension and transparency of information to facilitate acceptance and uptake.

There are likely to be concerns associated with COVID-19 vaccines given the accelerated pace of vaccine development, mistrust of the pandemic response by governments and growing suspicion regarding vaccines in some population groups.1-4 As for all new vaccines, there is the possibility that rare adverse reactions will not be identified in clinical trials and only found once a large number of people are vaccinated.  Additionally, when vaccinating large number of people, some of them will have adverse health outcomes shortly after vaccination by chance alone.  COVID-19 vaccine safety concerns need to be urgently addressed. The CONSIDER group was developed to provide responses to common COVID-19 vaccine safety questions that are understandable and accessible to key stakeholders.

Each answer is written by an expert member of the WG and reviewed by two or more other members.

Science is evolving rapidly. As more questions come to the group’s attention or more information becomes available (from COVID-19 vaccine clinical trials and early experience with vaccine introduction in countries), the answers will be updated and new answers will be posted. The questions and answers are hosted on this page and are cross-referenced on other sites.

The information provided on this page is written by an international group of experts in immunization and is applicable globally, including in the Canadian context.

Below is the latest version of the answers.  This webpage will be updated as new answers are added. 


  1. Schaffer DeRoo S, Pudalov NJ, Fu LY. Planning for a COVID-19 Vaccination Program. JAMA. 2020; 323(24):2458-2459. doi:10.1001/jama.2020.8711
  2. Lancet COVID-19 Commissioners, Task Force Chairs, and Commission Secretariat. Lancet COVID-19 Commission Statement on the occasion of the 75th session of the UN General Assembly. Lancet. 2020:S0140-6736(20)31927-9. doi: 10.1016/S0140-6736(20)31927-9.
  3. Kochhar S, Salmon DA. Planning for COVID-19 vaccines safety surveillance. Vaccine. 2020 Sep 11;38(40):6194-6198. doi: 10.1016/j.vaccine.2020.07.013
  4. MacDonald NE, Dube E. Vaccine safety concerns: Should we be changing the way we support immunization? EClinicalMedicine. 2020 Jun; 23:100402. doi: 10.1016/j.eclinm.2020.100402.
Multiple Languages | Share your Questions | Suggested Edits for Answered Questions 

COVID-19 Vaccine Safety Q & A

Clinical Trials Related

1. How is vaccine safety determined prior to vaccine use? 

Eve Dubé and Q&A Team

Unlike drugs that are given to ill people for cure, vaccines are given to healthy people to prevent disease. Thus, vaccines usually require higher proof of safety than therapeutic drugs before being used. Vaccine development undergoes a rigorous set of carefully implemented scientific and ethical processes and procedures to ensure safety and efficacy of vaccines before they are given to a large number of people (see MacDonald and Law1 on the Canadian vaccine safety system, very similar approaches are used in many other countries).
First, vaccine safety and immunogenicity (i.e., ability of the vaccine to produce an immune response) are assessed in pre-clinical studies using tissue-culture, cell-culture or animal models (e.g., tests with mice, ferrets or monkeys). If pre-clinical studies are successful (both safety and immunogenicity), clinical studies with humans are conducted. At each stage, the data of the studies and trials are assessed by government regulators to give permission to move to the next stage.

Phase I trials involve a small group of adults (generally between 20-100 healthy volunteers) and aim to assess the safety of the vaccine and the type and extent of immune response. If no issues are identified during Phase I, the experimental vaccine progresses to Phase II trials involving several hundreds of individuals. The goal of Phase II trials is to assess the vaccine’s safety, immunogenicity, dosing, and schedule. If successful, larger Phase III trials are conducted with thousands to tens of thousands of people to assess efficacy and further study safety. These are randomized and double-blind trials where the candidate vaccine is being tested against a comparison or placebo (usually an inert substance, such as a saline injection). Phase III Trials allow for the detection of rare side effects that are too infrequent to be identified in Phase I or Phase II Trials (e.g., occur in less than 1 to 10/10,000).2
The information on vaccine safety and efficacy from these trials is then assessed by government regulators who are independent from the researchers who conducted the trials or the vaccine manufacturers. Often non-governmental experts review the data as well.  After careful review of the data and approval by the regulators, the vaccine can be used in that country. Vaccine safety still continues to be monitored once the vaccine has been approved through active and passive surveillance to ensure that possible risks of very rare side effects associated with the vaccine are identified (reference to last question in the section on long term effect).
COVID-19 vaccine development is following these standards, even if the vaccines are being developed rapidly (reference to Question 4).3 Many COVID-19 vaccines are developed using approaches and technologies that have proven safe with other vaccines or drugs in the past, others use novel technologies. As with all new vaccines, great care and attention will be paid to vaccine safety.


  1. MacDonald NE, Law BJ. Canada’s eight-component vaccine safety system: A primer for health care workers. Paediatrics & Child Health, 2017, e13-16 Online: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5825834/pdf/pxx073.pdf Page Accessed September 28, 2020

  2. Vaccine Testing and Approval Process. Centers for Disease Control and Prevention. Online: https://www.cdc.gov/vaccines/basics/test-approve.html Page Accessed on September 25, 2020

  3. Accelerating a safe and effective COVID-19 vaccine. World Health Organization. Online: https://www.who.int/emergencies/diseases/novel-coronavirus-2019/global-research-on-novel-coronavirus-2019-ncov/accelerating-a-safe-and-effective-covid-19-vaccine Page Accessed on September 25, 2020

2. What measures ensure safe vaccines?

Janice  Graham and Q&A Team

Many checks (laws, regulations, and guidelines) help ensure the vaccines approved by National Regulatory Authorities (NRAs), such as the U.S. Food and Drug Administration, Health Canada, and the European Medicines Agency (EMA), are safe and efficacious. NRAs oversee the approval of clinical trials and carefully evaluate the evidence before a vaccine or therapeutic drug or device is approved in their countries. Institutional Research Ethics Boards (IRBs or REBs) determine whether clinical trial protocols meet ethical standards for informed consent, decision-making capacity, trial conduct, fairness and equity in research participation, privacy and confidentiality, conflicts of interest, safety monitoring and reporting, and registration (e.g., Canada's Tri-Council Panel on Research Ethics). International bodies, e.g., the International Conference on Harmonization (ICH) of Good Clinical Practice guideline, oversee research in humans and regulatory obligations for safety, efficacy and quality.1

Each clinical trial has a Data Safety Monitoring Board that evaluates interim data at predetermined intervals during the trial. Trials are paused when an untoward event occurs and can be stopped completely if continuation is deemed to be unmerited. The World Health Organization (WHO) coordinates expert advisory panels to deliberate on matters of global health, provides ethical guidance, and works with NRAs to license safe vaccines in low income countries. WHO encourages countries to have an independent national immunization technical advisory group (NITAG) to review the approved vaccine data in respect of the local epidemiology to determine who, if any, should receive the vaccine. NITAGs build capacity for global vaccine safety standards.2,3
Transparency throughout the vaccine pre-approval lifecycle is critical for safety and public trust, including review of all trial protocols, all data and technical documents, clinical study reports, stopping rules, and decision-making processes.4,5 Exceptional needs for urgent research during public health emergencies can guide ethics review and create mandates for NRAs to expedite regulatory pathways for clinical trials, consider conditional approvals and/or issue emergency use authorization. Despite some political pressure, NRAs in Canada, US and Europe have resisted taking shortcuts. Faster approval requires vigilance to ensure safety is not compromised.6,7,8  

Regulatory and legal standards limiting conflict of interest, enforcing manufacturing quality and the reporting of serious AEFIs ensure safety. To instill confidence that expedited COVID-19 vaccines will be safe, the public needs assurance of:

  1.  Clear disclosure guidelines that exclude those with perceived conflict of interest (personal and professional) from being involved in decisions;
  2. Transparency and open access to all trial protocols, data (including components of the vaccine such as adjuvants), amendments and adaptations, and decision-making processes and rationales;
  3. No increased participant risk from modifications made in adaptive trials that compress testing phases or add new arms in response to new findings. If, as GAVI  states “These changes aren’t guesswork - they are based on clearly defined rules that have been set up by scientists who are experts at evaluating uncertainty”,9 these modifications should be made immediately known, i.e., transparent, with rationale and data/evidence supporting those decisions;
  4. Independent appraisal of all clinical trial evidence and decision-making rationale, advisory committee recommendations and vaccine  promotion to address perception of conflict of interest;
  5. Sufficiently powered trials to ensure safety as well as efficacy. Phase III trials can miss rare (occurrence rate ≥ 0.01% and < 0.1%) but serious adverse events if trial participant numbers are small. Large trial populations are important in identifying rare and very rare but serious AEs that can result in morbidity (e.g., intussusception with Rotashield);
  6. Post-approval monitoring and active surveillance must be in place to detect very rare but serious adverse events following vaccination as well as detection of vaccine failures;
  7. Disease prevention rather than surrogate (e.g. serological) endpoints are a higher standard;
  8. Locating Phase III trials where the disease is prevalent is critical to disease exposure and the determination of disease prevention;
  9. With no available cures for COVID-19, human challenge trials are currently unethical.
  10. Equitable participation in research of under-represented communities at risk for serious disease, i.e., older adults, racial/ethnic groups, pregnant and immunocompromised persons.


  1. Dixon, J.R. The International Conference on Harmonization Good Clinical Practice guideline. Quality Assurance 1998; 6(2):65-74.  doi: 10.1080/105294199277860.
  2. Graham, J.E, Borda-Rodrigeuz, A., Huzair, F., &  Zinck, E. Capacity for a global vaccine safety system: The perspective of national regulatory authorities. Vaccine, 2012; 30(33), 4953-4959. doi:10.1016/j.vaccine.2012 .05.045.
  3. Harmon, S.H.E., Faour, D.E., MacDonald, N.E., Graham, J.E., Steffen C., Henaff L, Shendale S., the Global NITAG Network Survey Correspondents. Immunization governance: Mandatory immunization in 28 Global NITAG Network countries. Vaccine https://doi.org/10.1016/j.vaccine.2020.09.053
  4. Morten C.J., Kapczynski A, Krumholz HM, Ross, J.S. To help develop the safest, most effective coronavirus tests, treatments, and vaccines, ensure public access to clinical research data. Health Affairs Blog, March 26, 2020. https://www.healthaffairs.org/do/10.1377/hblog20200326.869114/full/
  5. Herder, Matthew and Janice E. Graham. Opinion: Herder and Graham: Canadians need and deserve transparency on COVID-19 vaccines. Ottawa Citizen Sept 15, 2020. https://ottawacitizen.com/opinion/herder-and-graham-canadians-need-and-deserve-transparency-on-covid-19-vaccines
  6. Graham, J.E. Smart Regulation: Will the government’s strategy work? Canadian Medical Association Journal 2005;173(12),1469-1470. doi: 10.1503/cmaj.050424. Retrieved from https://www.cmaj.ca/content/173/12/1469.short
  7. Graham, J.E., & Nuttall, R. Faster Access to New Drugs: Fault Lines Between Health Canada’s Regulatory Intent and Industry Innovation Practices. Ethics in Biology, Engineering & Medicine – An International Journal 2013;4(3),231-239. doi: 10.1615/EthicsBiologyEngMed.2014010771. (http://hdl.handle.net/10222/75934)
  8. Doshi, P. Pandemrix vaccine: why was the public not told of early warning signs? BMJ 2018;362:k3948 doi: 10.1136/bmj.k3948.  
  9. GAVI. Can vaccine clinical trials be sped up safely for COVID-19? https://www.gavi.org/vaccineswork/how-covid-19-leading-innovation-clinical-trials

3. Why was the Oxford vaccine clinical trial stopped and how was the vaccine safety determined?

Hanna Nohynek and Q&A Team

One study participant developed weakness in the arms and legs after vaccination, and a provisional diagnosis of transverse myelitis, an inflammatory syndrome that affects the spinal cord, was made. On further assessment, it was acknowledged that another participant had been diagnosed with multiple sclerosis, which also was deemed to be unrelated to the COVID-19 vaccine.1 In large trials with tens of thousands of participants, these types of pauses are not uncommon. Illnesses can happen by chance but must be independently reviewed to clarify whether or not they are linked to the medicine or vaccine being studied. In this case, the independent experts came to a conclusion that the vaccine did not cause these events, and the study was allowed to continue recruiting in the UK, South Africa, Brazil, Japan and the US.


  1. AstraZeneca and J&J get go-ahead to resume Covid-19 vaccine trials. Accessed on October 26, 2020 at https://www.ft.com/content/2d2d0e8c-3560-456f-bf3e-59a869e6aa00

Vaccine Introduction in Countries

1. What is meant by benefit-risk assessment of the vaccine in high priority populations? 

Sonali Kochhar and Q&A Team

Vaccination is one of the most successful public health interventions for disease prevention.1 Vaccines are given to healthy people, including very young children and vulnerable people, and therefore the acceptable level of risk from vaccines is very low. It is essential that vaccines have a highly favorable benefit-risk balance i.e. the benefits of vaccination must be significantly greater when compared to any risk of harm. This ensures appropriate and informed public health decision making.2

Benefit-risk assessment is the basis of regulatory decisions for all vaccines and drugs during the pre and post licensure review processes.2,3 Authorization for a vaccine or drug use is granted only if the benefit-risk assessment shows a sufficient positive benefit-risk balance based on the scientific evidence.3
The benefit-risk assessment of a vaccine or drug might be different for specific populations (e.g., children, pregnant women, and immunocompromised people), and for people at high versus low risk of disease (e.g, living in an area with an active outbreak).3

The benefit-risk assessment takes into consideration a number of factors including the severity of the disease, how well currently available medicines for the disease address the population’s medical needs, the effectiveness of the vaccine in preventing disease in specific populations, and the risk of adverse events following vaccination in the same populations compared with the risk associated with the disease.2,3,4

As an example for measles vaccine, the benefit of vaccines far outweighs the risks (the risk of adverse events following vaccination needs to be compared with the risk associated with the disease. The risk of side-effects of the treatment used to alleviate the symptoms of the disease are also taken into account).5

Benefit-Risk Assessment of Measles vaccine5
(Risk of adverse events following vaccination compared with the risk associated with the disease and risk of side-effects of the treatment used to alleviate the symptoms of the disease)

Benefit-Risk Assessment of Measles vaccine balance scale

Benefit-Risk Assessment of Measles vaccine table


  1. Rémy V, Zöllner Y, Heckmann U. Vaccination: the cornerstone of an efficient healthcare system. J Mark Access Health Policy. 2015;3:10.3402/jmahp.v3.27041. doi:10.3402/jmahp.v3.27041
  2. Arlegui, H., Bollaerts, K., Salvo, F. et al. Benefit–Risk Assessment of Vaccines. Part I: A Systematic Review to Identify and Describe Studies About Quantitative Benefit–Risk Models Applied to Vaccines. Drug Saf (2020). https://doi.org/10.1007/s40264-020-00984-7
  3. Benefit-risk assessment in drug regulatory decision-making. Draft PDUFA VI Implementation Plan (FY 2018-2022). FDA. March 30, 2018. Accessed on Sept 30, 2020 at https://www.fda.gov/media/112570/download
  4. Curtin F, Schulz P. Assessing the benefit: risk ratio of a drug--randomized and naturalistic evidence. Dialogues Clin Neurosci. 2011;13(2):183-90. PMID: 21842615; PMCID: PMC3181998.
  5. Risk  scales : benefits of vaccines far outweigh the risks. WHO Europe. Accessed on Oct  9,  2020 at https://www.euro.who.int/en/health-topics/disease-prevention/vaccines-and-immunization/publications/2017/risk-scales-benefits-of-vaccines-far-outweigh-the-risks-2017

2. What are the common side effects expected with the vaccines?

Youngmee Jee and Q&A Team

Vaccine related side effects are any health problem shown by studies to be caused by a vaccine. On the other hand, adverse events are any health problems that happen after vaccination that might be coincidental or related to the vaccine.

We do not yet have enough trial data to say what will be the minor and serious adverse events with the new COVID-19 vaccines. However, we do know about adverse events with other types of injectable vaccines.

  • Minor common side effects can be pain at injection site, redness/ swelling at injection site, low-grade fever, fatigue, headache, and minor muscle and/or joint pain (see Table 1).1 Usually these minor side effects occur within a few hours of injection but will go away within a few days.
  • Severe side effects such as seizures, thrombocytopenia, prolonged crying can occur rarely but usually do not result in long term problems.1
  • Allergic reactions such as anaphylaxis are very rare but can occur immediately (usually within minutes) after vaccination (e.g., due to a vaccine component such as neomycin) and can be life-threatening. Healthcare providers should be prepared to treat the symptoms of anaphylaxis.1
  • Vaccine adverse events can be classified into 5 categories:
    1. vaccine product-related reaction,
    2. vaccine quality detect-related reaction,
    3. immunization error-related reaction,
    4. immunization stress-related reaction and
    5. coincidental event.1
  • Adverse events following immunization is considered serious if it results in death, is life-threatening, requires in-patient hospitalization or prolongation of existing hospitalization, persistent or significant disability/incapacity, is a congenital anomaly/birth defect or requires intervention to prevent impairment of damage. Expected rates of AEFI following some childhood vaccines are provided at https://vaccine-safety-training.org/.1
  • Safety data from phase III trials of Pfizer COVID-19 vaccine2 showed common side effects such as headache, chills, joint pain, diarrhea and chills were less among older age groups than younger age groups. Most side effects after the second dose were mild to moderate. . All data will be carefully assessed by regulators in their decision of whether a vaccine will be approved for use or not.
  • The Moderna COVID-19 vaccine’s reported safety profile3 also showed minor common side effects. Of note, systemic adverse events were more common following the second dose and in those receiving the highest dose.
  • COVID-19 vaccines that complete phase 3 trials having been administered to 20,000 individuals or more with very few or no serious adverse effects and are shown to be efficacious are likely to receive regulatory approval for use.4

Table 1. Common, minor vaccine reactions and treatment

Table 1. Common, minor vaccine reactions and treatment
1. Local reactogenicity varies from one vaccine brand to another, depending on the strain and the number of viable antigen in the vaccine.
2. Diarrhoea, headache and/or muscle pains.
3. When compared with whole cell pertussis (DTwP) vaccine, acellular pertussis (DTaP) vaccine rates are lower.
4. Rate of local reactions are likely to increase with booster doses, up to 50 – 85%.
5. Source: http://www.cdc.gov/vaccines/hcp/acip-recs/
6. Paracetamol dose: up to 15mg/kg every 6–8 hours, maximum of 4 doses in 24 hours.
Source: WHO Vaccine safety basics e-learning course (module 3: Adverse events following immunization)


  1. WHO vaccine safety basics e-learning course. Accessed on 18 Oct 2020 at https://vaccine-safety-training.org/

  2. Pfizer says Covid-19 vaccine showed moderate side effects. Accessed on  

  3. Anderson EJ, Rouphael NG, Widge AT, Jackson LA, Roberts PC et al.  Safety and Immunogenicity of SARS-CoV-2 mRNA-1273 Vaccine in Older Adults. N Engl J Med. 2020 Sep 29. doi: 10.1056/NEJMoa2028436.

  4. Grech V, Calleja N. Theoretical novel COVID-19 vaccination risk of rare and severe adverse events versus COVID-19 mortality. Early Hum Dev. 2020 Oct 1:105212. doi: 10.1016/j.earlhumdev.2020.105212.

3. What will be the measures taken if a vaccine recipient experiences a side effect?

Noni MacDonald and Q&A Panel

Side effects are called adverse events – and those following immunization, Adverse Events Following Immunization (AEFI).
“Any untoward medical occurrence which follows immunization and which does not necessarily have a causal relationship with the usage of the vaccine. The adverse event may be any unfavourable or unintended sign, abnormal laboratory finding, symptom or disease.” 1

Common, minor AEFIs with different types of immunizations including signs and symptoms such as low grade fever, muscle pain, body ache, local pain, redness and/or swelling at the injection site, usually occur in less than 20% of the vaccine recipients within a few hours of the injection, resolve after a short period of time and have no long term consequences. With any new vaccine such as the COVID-19 vaccines, care will be paid to determine if minor AEFI occur in a similar rate as noted in the clinical trials and if these minor AEFI are more common in different age groups or in those with different underlying conditions, i.e. information that might not be available from the trials.

The intensity of the AEFI will be generally mild and can very rarely be moderate or severe (e.g. mild or moderate fever). Severe AEFI do not necessarily lead to long term problems.1

The AEFI that should draw attention quickly are “serious” AEFI.
“A serious AEFI is one that results in death, is life-threatening, requires in-patient hospitalization or prolongation of existing hospitalization, results in persistent or significant disability/incapacity, is a congenital anomaly/birth defect, or requires intervention to prevent permanent impairment or damage.1

Serious AEFI are usually not detected in the clinical trials because they are very rare, i.e. occur in less than 1 in 10,000 vaccine recipients. The critical point with serious AEFI, is to determine if the AEFI is due to the vaccine itself i.e. vaccine product-related reaction; is a vaccine quality defect-related reaction i.e. a vaccine manufacturing problem; is a program error; an immunization error-related reaction i.e. a program error such as improper vaccine storage, wrong diluent used etc.; an immunization stress-related reaction i.e. a coincidental event.1,2

Often events are coincidental. Note if the serious AEFI is indeed vaccine related,  corrective action i.e. recalling the vaccine may occur. However, due to the rigor of the prevaccine approval process, the rigor of the approval process as well as the high quality of manufacturing, rarely is the vaccine the problem in a serious AEFI.

Health care workers have several very important roles in relation to AEFI.  
a) Recognize and report serious AEFI and if requested also minor AEFI;
b) Provide care to the patient with the AEFI;
c) Help gather the case information that the Causality Assessment Committee will need to determine if the serious AEFI is vaccine related or not;3
d) Remain objective in reaching any conclusion about the cause of the AEFI.
e) Communicate in an effective, timely and respectful manner, grounded in the known facts of the event. The local public health programme should also be prepared to communicate on the event and steps being taken to investigate and establish causality.3,4 Work with them and your institution to ensure accurate information is supplied. Be sure to validate information and not perpetuate any misinformation.


  1. World Health Organization. Vaccine Safety Basics e-learning course.  Module 3. Adverse events following immunization. https://vaccine-safety-training.org/vaccine-reactions.html. Accessed Sept 24,2020

  2. Gold MS, MacDonald NE, McMurtry CM, Balakrishnan MR, Heininger U, Menning L, Benes O, Pless R, Zuber PLF. Immunization stress-related response - Redefining immunization anxiety-related reaction as an adverse event following immunization. Vaccine. 2020; 38(14):3015-3020.

  3. World Health Organization. Vaccine Safety Basics e learning course. Module 4: Surveillance. Causality Assessment of AEFIs. https://vaccine-safety-training.org/causality-assessment-of-aefis.html. Assessed Sept 24, 2020

  4. World Health Organization EUROPE. Crisis Communication Template (2017). https://www.euro.who.int/en/health-topics/disease-prevention/vaccines-and-immunization/publications/2017/crisis-communications-plan-template-2017. Accessed Sept 24, 2020

4. For a two dose vaccine, are there any safety considerations if the second dose of the vaccine is replaced by another vaccine?

Sonali Kochhar and Q&A Team

There are no data from the clinical trials to support the second dose of the vaccine being replaced by another COVID19 vaccine. It is recommended that the vaccine details are confirmed before immunization to ensure the correct vaccine product is given.

5. Should pregnant women receive the vaccine?

Sonali Kochhar and Q&A Team

There is evidence emerging that pregnant women might be at increased risk of serious disease from COVID-19 and there might be an increased risk of adverse pregnancy and birth outcomes as well.1,2,3 To date, there are no data regarding whether COVID-19 vaccines are safe or effective in pregnant women as they have been excluded from clinical trials. It is important that data specific to pregnant women are generated from their inclusion in later stage clinical trials, pregnancy-specific safety studies and follow up of trial participants who inadvertently become pregnant during Phase III clinical trials to inform public health recommendations for COVID vaccine use in this population.3,4


  1. Allotey J, Stallings E, Bonet M, Yap M, Chatterjee S et al for PregCOV-19 Living Systematic Review Consortium. Clinical manifestations, risk factors, and maternal and perinatal outcomes of coronavirus disease 2019 in pregnancy: living systematic review and meta-analysis. BMJ. 2020 Sep 1;370:m3320. doi: 10.1136/bmj.m3320.

  2. Ellington S, Strid P, Tong VT, Woodworth K, Galang RR, Zambrano LD, Nahabedian J, Anderson K, Gilboa SM. Characteristics of Women of Reproductive Age with Laboratory-Confirmed SARS-CoV-2 Infection by Pregnancy Status - United States, January 22-June 7, 2020. MMWR Morb Mortal Wkly Rep. 2020 Jun 26;69(25):769-775. doi: 10.15585/mmwr.mm6925a1. PMID: 32584795; PMCID: PMC7316319.

  3. Dashraath P, Nielsen-Saines K, Madhi SA, Baud D. COVID-19 vaccines and neglected pregnancy. Lancet. 2020 Sep 5;396(10252):e22. doi: 10.1016/S0140-6736(20)31822-5

  4. Heath PT, Le Doare K, Khalil A. Inclusion of pregnant women in COVID-19 vaccine development. Lancet Infect Dis. 2020 Sep;20(9):1007-1008. doi: 10.1016/S1473-3099(20)30638-1

Long term effects of vaccines

1. How will we know if a vaccine has long term safety concerns

Karina Top and Q&A Team

All vaccines approved for use by National Regulatory Authorities (NRAs) (e.g., US Food and Drug Administration (FDA) or Health Canada) are monitored for safety and effectiveness after introduction into the population. At a minimum, countries are recommended to implement passive surveillance systems that collect individual reports of adverse events following immunization from healthcare providers, vaccine manufacturers and often the public. These reports are collated and analyzed to identify any patterns that may suggest a safety concern with the vaccine (e.g., a certain condition reported more often after a specific vaccine than expected based on the background rate of that condition in the population). Countries that have the capacity are also recommended to institute active surveillance systems that search for cases of adverse events of special importance (e.g., seizures, Guillain Barré Syndrome) after immunization and compare rates of those conditions among vaccinated and unvaccinated groups to determine if the adverse events occurred by chance (which is commonly seen) or were related to the vaccine.

As done for any new vaccine, passive and active surveillance systems will be enhanced to identify specific adverse events of special importance following COVID-19 vaccines in a timely fashion. National and international public health organizations are already working to develop guidelines and strategies to ensure robust post-market safety monitoring of COVID-19 vaccines. The World Health Organization’s Global Advisory Committee on Vaccine Safety and the Brighton Collaboration, an international consortium of vaccine safety experts, in collaboration with the Coalition for Epidemic Preparedness Innovations (CEPI) are developing guidelines and case definitions for monitoring the safety of COVID-19 vaccines (expected to be available online December 2020).2


  1. Department of Immunization, Vaccines and Biologicals. 2012. Global Vaccine Safety Blueprint. Geneva: World Health Organization. Access at: https://www.who.int/vaccine_safety/publications/en/. Accessed: 5 October 2020.

  2. 2020. Global Advisory Committee on Vaccine Safety, 27-28 May 2020. Wkly Epidemiol Rec. 95:325-336. Access at: https://apps.who.int/iris/bitstream/handle/10665/333136/WER9528-eng-fre.pdf?ua=1. Accessed: 5 October 2020.

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