CPHA Canvax

COVID-19: Potential Impact on Vaccine-Preventable Diseases in Canada

Noni MacDonald, Eve Dubé, Lucie Marisa Bucci

Noni MacDonald, Dalhousie University
Eve Dubé, INSPQ
Lucie Marisa Bucci, Immunize Canada

The rapid spread of SARS-CoV-2 has led to an unprecedented number of COVID-19 cases and deaths globally, as well as in Canada. This microbe clearly knows no borders or a country’s wealth or health status (Worldometer - Coronavirus Cases). Given that there are no effective antivirus therapeutics or a vaccine as of yet, the major strategy for slowing the pandemic has been aggressive containment. This has included widespread testing, quarantine of cases, stay-at-home orders, school closures, physical distancing and community containment such as closing borders, restricting travel and curtailing all, but essential services (1; 2). Surveillance data are showing that the containment strategy is effective (3).

However, this containment strategy carries a hidden risk with respect to impeding routine immunization services. The 2020 COVID-19 guidance from the World Health Organization (WHO) has emphasized that routine immunization of children and some adults, and vaccine-preventable disease surveillance are essential services to deliver even during containment restrictions (4). Disruption of immunization services even for short periods of time can rapidly increase the number of individuals susceptible to a vaccine-preventable disease. For example, with the 2013-2014 Ebola outbreak in Liberia, the associated marked decrease in measles immunization lead to a six-fold increase in measles cases (5). Given the high potential for vaccine-preventable disease outbreaks during or following immunization service disruption, such as COVID-19-related disruption, WHO states that “it is imperative for countries to maintain continuity of immunization services wherever services can be conducted under safe conditions (4)”. Unfortunately, significant disruptions in routine immunization services have already happened due to health services being overwhelmed by the rapid increase in COVID-19 cases. In this context, it is more important than ever that the delivery of immunization programs be adapted to fit the ‘new’ context during the peak of the pandemic and for the recovery period.

Delivery settings vary by province or territory, spanning physicians’ and/or nurse practitioners’ offices, public health clinics, pharmacies, schools, and in some settings, nurse delivery in the home. With COVID-19, the extent of routine immunization disruption is unclear. Contributors include a lack of designation of immunization as an essential service, staffing concerns, the rollback of in-person primary care (more virtual care) and/or concerns about physical distancing in clinics. Also, some parents are afraid of potentially exposing their children to COVID-19 and may opt to cancel or delay routine infant vaccinations.

What does this mean for Canada?
A measles risk perspective.

Measles, the most contagious vaccine-preventable disease, is always a serious risk concern if coverage rates fall even slightly. In Canada, childhood measles immunization programs are not uniform with respect to age (12 months and 18 months, or 12 months and 4 to 5 years), the combination of vaccines used (MMRV or MMR + V), or the location where families can access these immunizations.

Prior to COVID-19, the published national rates for the first and second dose of measles vaccination were about 90% and 87%, respectively (Canada: WHO and UNICEF estimates of immunization coverage: 2018 revision). These rates, while “very good”, are not sufficient to provide community immunity, as rates over 95% (6) are needed should measles be introduced. Furthermore, infant and childhood immunization uptake rates have not been uniform across the country, leaving pockets with rates below 90%, with the impact of this well illustrated by previous measles outbreaks (7). These pockets of low vaccine uptake are often known to the local public health unit, and when a measles case occurs, steps are rapidly taken to provide the vaccine to the unimmunized (7; 8).

As an example of the potential risk of missed immunization, consider that in 2018 more than 380,000 babies were born in Canada (Number of births in Canada from 2000 to 2019). Focusing on infants turning one year and missing MMR dose 1, for each month that services are not available, up to 31,600 infants go unprotected. After 3 months, 95,000 would be unprotected, representing 25% of the infant cohort and a group large enough to fuel an outbreak. With the anticipated lifting of regional and international travel bans, the risk of importation of measles rises, potentially setting Canada on a path for endemic transmission and spreading within this measles-unimmunized cohort if they are not quickly caught up on their measles immunization.

What to do?
International Guidance

The WHO COVID-19 immunization guidance recommends temporarily postponing preventive mass immunization campaigns where there is no active outbreak of a vaccine-preventable disease, followed by rapid catch-up as soon as possible (4). Better still is the continuation of immunization through the containment period, which countries in several WHO regions have tried to ensure.

National Guidance

The National Advisory Committee on Immunization (NACI) recommends the prioritization of primary vaccination series of healthy infants and toddlers, and deems immunization as an essential service during the COVID-19 pandemic.* Within Canada, several provinces have already issued guidance on adapted vaccine delivery practices during COVID-19 containment, while other provinces have not changed beyond providing tips on how to enhance infection control practices for immunization clinics during COVID-19 (Immunize BC - Immunization during COVID-19).

Quebec provides an example for adapted nurse clinic delivery based on recommendations of the Comité sur l'immunisation with the focus on delivering immunization to infants at 2 months, 4 months and 12 months of age (i.e., including measles immunization through the local community service centres while still ensuring infection control procedures) (Vaccination activities during the COVID-19 coronavirus pandemic).

Ontario provides an adapted model where infant and early childhood vaccines are predominantly given by family physicians. The Ontario College of Family Physicians provides an interim guidance schedule for well-child visits with a mix of virtual visits (1 month, 9 months and 18 months) and in-person visits at 2, 4, 6, 12 and 15 months for immunization, with a postponement of the 4 to 6 year-old visit for immunization (Interim Schedule for Children and Pregnant Women during the COVID-19 Pandemic).

Creative measures to ease access and COVID-19 fear by preserving physical distancing and infection control need to be considered, such as drive-up access  ̶  a strategy currently employed by a family doctor in Toronto (Putting off kids' vaccines during COVID-19 heightens risk of other outbreaks – Drive-up vaccination)  ̶  and alternative access sites. The University of Toronto’s Dalla Lana School of Public Health’s Centre for Vaccine Preventable Disease has also recently provided guidance on the importance of maintaining immunization programs during COVID and how health care providers can continue to provide immunization during this period (Maintaining Immunization Programs Webinar). All provinces and territories need public health messaging on the importance of routine immunization, the options for access, and how the risk of exposure to COVID-19 is being minimized.

The vaccine uptake success rate is not known for either of these adapted models or for the provinces and territories where regular delivery has continued. It is highly probable that some infants and young children have been immunized but others were missed, or only partially immunized, or the immunization was postponed (e.g. 4- to 6-year-olds). As well, postponement of school-based immunization programs occurred across the country when schools were closed, representing another missed opportunity. The number and specific ages of all who have missed immunizations or are under-immunized are not yet known. It is imperative that these missed cohorts are identified and found so catch-up can occur (e.g. infants, young children, and school-age children, as well as adults) once COVID-19 containment efforts are loosened. This will be challenging and may require new ways of working.

The Importance of Immunization Records

Data collection to detect the missing is not simple, given our fragmented health data collection systems. None of our provinces or territories have fully integrated patient-centred e-health data systems linked across the life course to all health information and health system encounters and to vital statistics in their jurisdiction. Such systems are in place in several Caribbean countries (e.g., Belize (9)), making it much simpler to determine who is fully immunized, partially immunized or unimmunized regardless of age. Such systems can not only detect, but can also be set to flag those needing immunization whenever they are in contact with the health system, regardless of the reason for that contact (i.e., opportunity to catch up or a reminder to catch up).

In Canada, because of our fragmented health data collection system, we will need to ensure more public awareness and community engagement to try to catch up on missed immunizations regardless of age, as they may not be found through our traditional data collection systems. Self-identification can help. Given the growing recognition of the serious impact of COVID-19 on our society and appreciation amongst the public of the value of a vaccine to thwart it, there is an important opportunity here to raise the profile and importance of all regular immunizations across the life course.

Sending the Right Public Health Message

As soon as possible, provinces and territories should emphasize that immunization services are again available and important to access in modified formats. To catch up those who have been missed, special clinics and increased opportunities to access missed immunizations may be required such as ‘doubled-up’ school vaccine programs, extra hours for physicians or public health clinics, more vaccines offered by pharmacists, etc. How well Canada can ensure measles immunization catch-up may be our canary in the coal mine. Not attending to catching up those who have been missed is risky. Canada has experienced mumps outbreaks in young adults who had received only one dose of measles, mumps and rubella vaccine because catch-up programs for the second dose were not put in place when the routine two-dose regimens were started (10). Missing diphtheria immunizations may even lead to diphtheria cases, a disease rarely seen in Canada in recent years (11). All local public health agencies and physician management immunization services need to be proactive in catching those who have missed immunization during COVID-19. Public service messages, both in mainstream media and on social media platforms, will also be needed to alert those who have missed immunizations for their children or themselves on the importance of catching up.

*Edited May 19, 2020 - added recommendation from the National Advisory Committee on Immunization (NACI).


  1. Isolation, quarantine, social distancing and community containment: pivotal role for old-style public health measures in the novel coronavirus (2019-nCoV) outbreak. Wilder-Smith A, Freedman DO. 2, 2020, Journal of Travel Medicine, Vol. 27, pp. 1-4.
  2. COVID-19: towards controlling of a pandemic. Bedford J, Enria D, Giesecke J, Heymann DL, Ihekweazu C, Kobinger G, Lane HC, Memish Z, Oh MD, Sall AA, Schuchat A, Ungchusak K, Wieler LH, WHO Strategic and Technical Advisory Group for Infectious Hazards. 10229, 2020, Lancet , Vol. 395, pp. 1015-1018.
  3. First-wave COVID-19 transmissibility and severity in China outside Hubei after control measures, and second-wave scenario planning: a modelling impact assessment. Leung K, Wu JT, Liu D, Leung GM. April 8 ahead of print, 2020, Lancet, pp. pii: S0140-6736(20)30746-7.
  4. World Health Organization. Guiding principles for immunization activities during COVID-19 pandemic. s.l. : World Health Organization, March 26 2020.
  5. Did the Ebola outbreak disrupt immunisation services? A case study from Liberia. Wesseh CS, Najjemba R, Edwards JK, Owiti P, Tweya H, Bhat P. Supplement 1 , 2017, Public Health Action , Vol. 7, pp. S82-S87.
  6. Evaluation of the establishment of herd immunity in the population by means of serological surveys and vaccination coverage. Plans-Rubió P. 2, 2012, Hum Vaccin Immunother., Vol. 8, pp. 184-188.
  7. Outbreak of measles in an unvaccinated population, British Columbia, 2014. Naus M, Puddicombe D, Murti M, Fung C, Stam R, Loadman S, Krajden M, Tang P, Lem M. 7, Jul 2, 2015, Can Commun Dis Rep, Vol. 41, pp. 169-174.
  8. Prevalence of risk factors for acquiring measles during the 2011 outbreak in Quebec and impact of the province-wide school-based vaccination campaign on population immunity. Billard MN, De Serres G, Gariépy MC, Boulianne N, Toth E, Landry M, Skowronski DM. 10, Oct 11, 2017, PLoS One, Vol. 12, p. e0186070.
  9. Decline in mortality with the Belize Integrated Patient-Centred Country Wide Health Information System (BHIS) with embedded program management. Graven M, Allen P, Smith I, MacDonald NE. 10, 2013, Int J Med Inform, Vol. 82, pp. 954-63.
  10. Investigation and management of a large community mumps outbreak among young adults in Toronto, Canada, January 2017–February 2018. Dubey V, Ozaldin O, Shulman L, Stuart R, Maclachlan J, Bromley L, Summers A. 12, 2018, Can Commun Dis Rep, Vol. 44, pp. 309-316.
  11. Global Epidemiology of Diphtheria, 2000–2017. Clarke K, MacNeil A, Hadler S, Scott C, Tiwari TSP, Cherian T. 10, 2019, Emerging Infectious  Diseases, Vol. 25, pp. 1834-42.
  12. COVID19: learning from experience. Lancet, The. 10299, 2020, Lancet, Vol. 395, p. 1011.