NCT03748160

Brief Summary

The aim of this study is to test the effectiveness of communicating the concept of herd immunity on actual influenza vaccine uptake using a randomized controlled trial.

Trial Health

87
On Track

Trial Health Score

Automated assessment based on enrollment pace, timeline, and geographic reach

Enrollment
48,125

participants targeted

Target at P75+ for not_applicable

Timeline
Completed

Started Oct 2018

Geographic Reach
1 country

1 active site

Status
completed

Health score is calculated from publicly available data and should be used for screening purposes only.

Trial Relationships

Click on a node to explore related trials.

Study Timeline

Key milestones and dates

Study Start

First participant enrolled

October 1, 2018

Completed
1 month until next milestone

First Submitted

Initial submission to the registry

November 1, 2018

Completed
19 days until next milestone

First Posted

Study publicly available on registry

November 20, 2018

Completed
6 months until next milestone

Primary Completion

Last participant's last visit for primary outcome

June 1, 2019

Completed
7 months until next milestone

Study Completion

Last participant's last visit for all outcomes

December 31, 2019

Completed
Last Updated

August 20, 2025

Status Verified

August 1, 2025

Enrollment Period

8 months

First QC Date

November 1, 2018

Last Update Submit

August 18, 2025

Conditions

Influenza, Human

Outcome Measures

Primary Outcomes (1)

  • Vaccine uptake

    Number of influenza vaccinations in study population

    up to six months (beginning from November 1 / until April 30)

Other Outcomes (1)

  • Heterogeneity

    up to six months (beginning from November 1 / until April 30)

Study Arms (3)

Control

NO INTERVENTION

There is no intervention (letter) in the control arm. There is no control arm in the city of Espoo. 1/3 of subjects in all other municipalities are assigned to the control arm.

Mailing

ACTIVE COMPARATOR

This treatment arm consists of a standard letter reminding elderly citizens (65 years and above) about influenza vaccines that are available free of charge from the local health centers.

Other: Letter

Herd

ACTIVE COMPARATOR

This treatment arm consists of a letter that highlights the herd immunity effects of vaccination and reminds elderly citizens (65 years and above) about influenza vaccines that are available free of charge from the local health centers.

Other: Letter

Interventions

LetterOTHER

Intervention consists of two different types of postal letters reminding elderly citizens (65 years and above) about influenza vaccines that are available free of charge from the local health centers

HerdMailing

Eligibility Criteria

Age65 Years+
Sexall
Healthy VolunteersYes
Age GroupsOlder Adult (65+)

You may qualify if:

  • At least 65 year old citizens in the municipalities of Espoo, Maalahti, Korsnäs, Kristiinankaupunki, Kaskinen and Närpiö

Contact the study team to confirm eligibility.

Sponsors & Collaborators

Study Sites (1)

National Institute for Health and Welfare

Helsinki, 00271, Finland

Location

Related Publications (1)

  • Saaksvuori L, Betsch C, Nohynek H, Salo H, Sivela J, Bohm R. Information nudges for influenza vaccination: Evidence from a large-scale cluster-randomized controlled trial in Finland. PLoS Med. 2022 Feb 9;19(2):e1003919. doi: 10.1371/journal.pmed.1003919. eCollection 2022 Feb.

    PMID: 35139082DERIVED

MeSH Terms

Conditions

Influenza, Human

Interventions

College Fraternities and Sororities

Condition Hierarchy (Ancestors)

Respiratory Tract InfectionsInfectionsOrthomyxoviridae InfectionsRNA Virus InfectionsVirus DiseasesRespiratory Tract Diseases

Intervention Hierarchy (Ancestors)

OrganizationsHealth Care Economics and Organizations

Study Officials

  • Cornelia Betsch, PhD

    University of Erfurt

    PRINCIPAL INVESTIGATOR

  • Robert Böhm, PhD

    RTWH Aachen University

    PRINCIPAL INVESTIGATOR

  • Hanna Nohynek, PhD

    Finnish Institute for Health and Welfare

    PRINCIPAL INVESTIGATOR

  • Saila Pitkänen, MSc

    Finnish Institute for Health and Welfare

    PRINCIPAL INVESTIGATOR

  • Heini Salo, PhD

    Finnish Institute for Health and Welfare

    PRINCIPAL INVESTIGATOR

  • Lauri Sääksvuori, PhD

    Finnish Institute for Health and Welfare

    STUDY DIRECTOR

  • Jonas Sivelä, PhD

    Finnish Institute for Health and Welfare

    PRINCIPAL INVESTIGATOR

Study Design

Study Type
interventional
Phase
not applicable
Allocation
RANDOMIZED
Masking
QUADRUPLE
Who Masked
PARTICIPANT, CARE PROVIDER, INVESTIGATOR, OUTCOMES ASSESSOR
Purpose
PREVENTION
Intervention Model
PARALLEL
Model Details: Cluster (household) RCT with three treatment arms
Sponsor Type
OTHER GOV
Responsible Party
SPONSOR

Study Record Dates

First Submitted

November 1, 2018

First Posted

November 20, 2018

Study Start

October 1, 2018

Primary Completion

June 1, 2019

Study Completion

December 31, 2019

Last Updated

August 20, 2025

Record last verified: 2025-08

Locations

FI(1)