Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2011;6(12):e27897.
doi: 10.1371/journal.pone.0027897. Epub 2011 Dec 12.

Adverse events following 12 and 18 month vaccinations: a population-based, self-controlled case series analysis

Kumanan Wilson  1 , Steven Hawken, Jeffrey C Kwong, Shelley Deeks, Natasha S Crowcroft, Carl Van Walraven, Beth K Potter, Pranesh Chakraborty, Jennifer Keelan, Michael Pluscauskas, Doug Manuel
Affiliations

Adverse events following 12 and 18 month vaccinations: a population-based, self-controlled case series analysis

Kumanan Wilson et al. PLoS One. 2011.

Abstract

Background: Live vaccines have distinct safety profiles, potentially causing systemic reactions one to 2 weeks after administration. In the province of Ontario, Canada, live MMR vaccine is currently recommended at age 12 months and 18 months.

Methods: Using the self-controlled case series design we examined 271,495 12 month vaccinations and 184,312 18 month vaccinations to examine the relative incidence of the composite endpoint of emergency room visits or hospital admissions in consecutive one day intervals following vaccination. These were compared to a control period 20 to 28 days later. In a post-hoc analysis we examined the reasons for emergency room visits and the average acuity score at presentation for children during the at-risk period following the 12 month vaccine.

Results: Four to 12 days post 12 month vaccination, children had a 1.33 (1.29-1.38) increased relative incidence of the combined endpoint compared to the control period, or at least one event during the risk interval for every 168 children vaccinated. Ten to 12 days post 18 month vaccination, the relative incidence was 1.25 (95%, 1.17-1.33) which represented at least one excess event for every 730 children vaccinated. The primary reason for increased events was statistically significant elevations in emergency room visits following all vaccinations. There were non-significant increases in hospital admissions. There were an additional 20 febrile seizures for every 100,000 vaccinated at 12 months.

Conclusions: There are significantly elevated risks of primarily emergency room visits approximately one to two weeks following 12 and 18 month vaccination. Future studies should examine whether these events could be predicted or prevented.

PubMed Disclaimer

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Illustration of the self-controlled case series design.
The observation period for each patient begins with pediatric vaccination date (leftmost upward arrow) and continues for a total of 28 days. In the primary analyses, each day post vaccination is considered a risk interval, and consecutive days with a statistically significant t elevation in relative incidence were pooled to create a combined risk interval. Days 20–28 comprise the control interval. The intervening days represent the wash-out period.
Figure 2
Figure 2. Vaccination events by days since birth from days 340 to 700.
Count = number of individuals vaccinated on a given day. Days = number of days after date of birth.
Figure 3
Figure 3. Number of combined endpoints versus days before/after 12 month vaccination.
Count = number of combined endpoints of emergency room visit or hospitalization. Days = number of days before or after vaccination, day 0 being the day of vaccination.
Figure 4
Figure 4. Number of combined endpoints versus days before/after 18 month vaccination.
Count = number of combined endpoints of emergency room visit or hospitalization. Days = number of days before or after vaccination, day 0 being the day of vaccination.
Figure 5
Figure 5. Historical analysis of combined endpoints versus days following 12 and 18 month vaccination: April 2002–March 2005.
a) Before/after 12 month vaccination. b) Before/after 18 month vaccination. Count = number of combined endpoints of emergency room visit or hospitalization. Days = number of days before or after vaccination, day 0 being the day of vaccination.
See this image and copyright information in PMC

References

    1. Stratton KR, Howe CJ, Johnston RB, editors. Adverse Events Associated with Childhood Vaccines: Evidence Bearing on Causality. Washington, DC: National Academy Press; 1994. - PubMed
    1. Siegrist CA. Mechanisms underlying adverse reactions to vaccines. J Comp Pathol. 2007;137(Suppl 1):S46–50. - PubMed
    1. Strebel PM, Papania MJ, Halsey NA. Measles vaccine. In: Plotkin SA, Orenstein WA, editors. Vaccines. 4th ed. Philadelphia: Saunders; 2004.
    1. Fritzell B. Detection of adverse events: what are the current sensitivity limits during clinical development? Vaccine. 2001;20(Suppl 1):S47–48. - PubMed
    1. Barlow WE, Davis RL, Glasser JW, Rhodes PH, Thompson RS, et al. The risk of seizures after receipt of whole-cell pertussis or measles, mumps, and rubella vaccine. N Engl J Med. 2001;345:656–661. - PubMed

Publication types