The Effect of Simultaneous Versus Sequential Intramuscular Vaccine Injections on Pain Levels in Infants

March 2, 2026 updated by: Sevil Inal, Istanbul University - Cerrahpasa

The Effect of Simultaneous Versus Sequential Intramuscular Vaccine Injections on Pain Levels in Infants: a Randomized Controlled Trial

This study was designed as a randomized controlled trial comparing simultaneous and sequential administration of intramuscular vaccines in infants.

Study Overview

Status

Completed

Conditions

Intervention / Treatment

Detailed Description

The study was carried out in the pediatric outpatient vaccination clinic of a private hospital in Istanbul, Türkiye, between 1 September and 15 November 2021.

Infants were eligible if they were younger than 12 months, required two routine intramuscular vaccines during the same visit, and were accompanied by a parent or legal guardian able to provide informed consent.

Infants were excluded if they had received analgesics within six hours prior to vaccination, received vaccines other than hepatitis B, pentavalent combination vaccine (DTaP-IPV/Hib), or pneumococcal conjugate vaccine, or had known neurological, developmental, or motor impairments.

Infants were randomly assigned in a 1:1 ratio to either the simultaneous injection group or the sequential injection group using computer-generated randomization (www.randomizer.org). Allocation was completed prior to the vaccination procedure.

A total of 150 infants were assessed for eligibility; 40 did not meet inclusion criteria. The final sample included 110 infants (55 per group). No participants were lost to follow-up.

Study Type

Interventional

Enrollment (Actual)

110

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • Turkey (Türkiye)
    • İ̇stanbul
      • Istanbul, İ̇stanbul, Turkey (Türkiye), 34500
        • Koc University

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Child

Accepts Healthy Volunteers

Yes

Description

Inclusion Criteria:

  • The following criteria were determined: the child was ordered to receive two of the routine childhood IM vaccines (hepatitis B, quintuple combination vaccine, pneumococcal vaccine), the parents were willing to participate in the study, the child had not received painkillers in the last 6 hours, and the child did not have mental and motor retardation.

Exclusion Criteria:

  • It was determined that the child should be 1 year of age or older, the vaccines other than the quintuple mixed vaccine, Pneumococcal vaccine and Hepatitis B vaccine should have been ordered by the physician.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Supportive Care
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: Single

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: Simultaneous injection group
Two trained pediatric nurses administered the vaccines simultaneously into different thighs (vastus lateralis muscles) following a coordinated countdown.
Other: Simultaneous injection
Two trained pediatric nurses administered the vaccines simultaneously into different thighs (vastus lateralis muscles) following a coordinated countdown.
Other: Sequential injection group

A single nurse administered the two vaccines consecutively into different thighs. A pause of approximately 10-15 seconds between injections allowed the infant to settle.

Vaccinations were performed individually in a quiet room to prevent distraction or distress from other children. Infants were positioned on an examination stretcher with the thigh exposed.
Other: Sequential injection
A single nurse administered the two vaccines consecutively into different thighs. A pause of approximately 10-15 seconds between injections allowed the infant to settle.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Pain was assessed using the FLACC
Time Frame: Time Frame: Baseline; During injection (periprocedural); Immediately after injection (within 1 minute)
The scale has 5 behavioral assessment categories (facial expression, leg movement, activity, crying, consolability). Each category consists of three items and is scored between 0 and 2 points. The total scale score ranges from 0 to10, with higher scores indicating greater pain intensity.
Time Frame: Baseline; During injection (periprocedural); Immediately after injection (within 1 minute)

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Istanbul University - Cerrahpasa

Investigators

  • Study Director: Sevil Inal, Istanbul University - Cerrahpasa

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

September 1, 2021

Primary Completion (Actual)

November 15, 2021

Study Completion (Actual)

November 15, 2021

Study Registration Dates

First Submitted

February 25, 2026

First Submitted That Met QC Criteria

March 2, 2026

First Posted (Actual)

March 6, 2026

Study Record Updates

Last Update Posted (Actual)

March 6, 2026

Last Update Submitted That Met QC Criteria

March 2, 2026

Last Verified

March 1, 2026

More Information

Terms related to this study

Keywords

Other Study ID Numbers

  • IUCerrahpasaRCT

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

IPD Plan Description

Institutional policy does not allow

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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