Priority populations experiences of isolation, quarantine and distancing for COVID-19: protocol for a longitudinal cohort study (Optimise Study)

Optimise Study collaborators implement additional substudies of specific priority populations to increase the breadth and depth of the findings. Information is reported frequently to governments and the community. We used the Standard Protocol Items: Recommendations for Interventional Trials reporting guidelines33 and details of Optimise Study registry information are detailed in online supplemental file 1 (table 1).

Longitudinal cohort

Study design

The longitudinal cohort and social network study aims to recruit approximately 1000 Victorians. It involves social network analysis to inform responses to COVID-19, so uses snowball sampling for recruitment and collects data on the interactions and connections between participants to understand transfer of knowledge, attitudes and practices.34 35 It targets priority populations considered to be at risk of contracting COVID-19, developing severe COVID-19, experiencing negative impacts of government restrictions introduced to reduce COVID-19 transmission, or having difficulty understanding or following restrictions. ‘Seed’ participants are from selected priority populations, meaning the cohort does not represent the broader Victorian population.

Optimise recruits from two groups:

  • Group 1: people diagnosed with COVID-19 (within the past 7 days) or notified as ‘close contacts’ of a person with COVID-19.

  • Group 2: people not currently infected with COVID-19 but at heightened risk of infection and/or adverse outcomes of COVID-19 infection and/or public health measures (eg, worse employment conditions, housing or access to primary healthcare).

Over the study, participants complete 16 data collection tools at baseline (one key people nomination, one baseline survey, then 14 prospective daily diaries) then five data collection points each month (one monthly follow-up survey and four follow-up diaries), plus additional surveys if they test positive for COVID-19 or are a close contact.

Sampling and sample size

Snowball sampling was used to recruit individuals and their contacts. Seeds are sampled purposively from priority populations (layer 0) and asked to nominate people they consider ‘key’ in their day-to-day lives (meaning relatives, people with whom they live, discuss personal matters, give or receive practical support, interact frequently, and/or share hobbies or sport; ‘key people’ hereafter). Layer 0’s key people are recruited (layer 1 participants), and nominate their own key people (layer 2) (figure 1). Layer 2 participants are asked to nominate key people, for the purposes of social network analysis, but they are not recruited.

Figure 1
Figure 1

Example of snowball recruitment for the Optimise Study.

The study aimed to recruit ~1000 participants, based on 200 seed participants and anticipating 1–2 key people recruited from each participant in layers 1 and 2. Sample size calculations were based on targets for priority groups. Layer 0 target numbers were revised as the study progressed to respond to pandemic dynamics and emerging priority populations, and because fewer key people (layers 1 and 2) were recruited than anticipated. Additional priority populations and targets were introduced throughout the follow-up period as the epidemiology evolved and new priority populations were identified. Priority populations and targets are shown in table 1. Definitions of priority populations, sampling strategies and COVID-19 case definitions are included in online supplemental file 1 (table 2).

Table 2

Overview of data collection tools and scheduling


Participants are eligible if they are in a target group and meet the following inclusion criteria:

  • Aged ≥18 years.

  • Resident of Victoria, Australia.

  • Willing and able to provide informed consent to participate in a survey/interview over the phone in English, or in Arabic, Mandarin or Dinka (AMD) when a bilingual data collector is available.

  • Provide a valid email (Participants completing all tools by phone interview do not require an email address for study communications, but, if available it is recorded to assist with conflict resolution in social network analysis.) and phone number.

  • Have access to the internet to complete online surveys or a phone to undertake phone interviews.

Participants are excluded if they are:


Seeds are recruited through paid and unpaid social media advertisements and flyers distributed via community and industry groups, community-based organisations and professional networks. Targeted social media advertisements reach priority groups based on age range, location, setting, gender and self-nominated interests (eg, health and social welfare). Advertisements and flyers direct potential participants to the study website, where they can submit an expression of interest (EOI).36 The EOI includes questions to categorise seeds and assess their eligibility (table 1).

In September 2021, specific recruitment and data collection strategies were developed to enable people born overseas or speaking a language other than English at home to participate.37 Trained bilingual data collectors from AMD-speaking communities were employed to support recruitment and data collection in participants’ languages. Data collectors use online advertisements, flyers and posters translated into AMD (with English). Flyers and posters are distributed to community service organisations and promoted on local AMD-language radio stations and social media platforms, including WeChat, Weibo and WhatsApp.

EOI forms translated into Arabic and simplified Chinese were available on the study website; Dinka is primarily a verbal language, so the EOI form is in English with some accompanying Dinka translation. Bilingual data collectors aimed to prioritise recruitment of participants who face additional barriers to accessing information and support during the COVID-19 pandemic. They used the following additional recruitment criteria: people with: low English proficiency, low technological proficiency (ie, could not self-complete surveys), have recently emigrated to Australia and are ineligible for government support.

When feasible, each participant is assigned a single data collector responsible for communication and follow-up to promote continuity and rapport. All potential participants receive an initial phone call from a data collector who explains the study, including its aims, procedures, participation requirements and reimbursements. When a potential participant expresses interest, the data collector administers the screening questions, confirms eligibility and records consent (see online supplemental file 2). Informed consents are provided by all participants to enter the cohort, collected verbally and documented in the study database, with additional consent provided prior to any of the substudies. Data collectors abandon recruitment after three unsuccessful contact attempts or if the study candidate declines.

Data collection procedures

We collect data across a broad range of domains, including sociodemographics, work and study circumstances, finances, health behaviours, access to services and information, social connectedness, mental health, knowledge of COVID-19, attitudes towards COVID-19 prevention measures and contact with people. Data collection follows a standardised and high-frequency procedure, including once-off surveys, baseline surveys and contact diaries, repeated monthly follow-up surveys, repeated weekly follow-up contact diaries, and COVID-19 event-based diaries. Recruitment into the longitudinal cohort commenced in September 2020 and closed in December 2021 when the target sample size was achieved. Once funding was secured to support recruitment of new priority populations, including from AMD-speaking communities, follow-up was extended and participants could complete up to 24 months of monthly follow-up surveys and diaries and annual surveys for up to 48 months to allow ongoing generation of data to inform public health policy (September 2020 to December 2024). In addition to the standardised longitudinal data collection, cross-sectional snapshot surveys were developed and deployed ad hoc across 2021–2023 to collect more in-depth data on participants’ behaviours and attitudes to new government policies and COVID-19 mitigation strategies.

Participants can withdraw from the study at any time by emailing the study team or sending an SMS. We unenrol participants who have not completed a baseline survey within 10 days of recruitment and are unresponsive to repeated follow-up attempts.

Baseline data collection

An interview guide for all data collection tools was translated into AMD through an accredited translation service and reviewed by our bilingual data collectors for cultural appropriateness. Following consent, participants complete a phone interview with a data collector who administers the key people form and asks participants to designate their preferred data collection method:

  • All tools are interviewer-administered by telephone in the relevant language.

  • Self-complete daily contact diaries and follow-up contact diaries in English, Mandarin and Arabic. Consent, key people, retrospective diary, baseline and follow-up surveys are administered over the phone with a bilingual data collector.

  • Participants who speak a language other than English at home and are fluent in English can self-complete all tools in English.

Participants are automatically assigned to the relevant data collection tools and subsequent schedule of surveys and diaries for the follow-up period (see figure 2 and table 2). For self-administered tools, the participant is sent a secure link by email and/or SMS (as preferred). Automated reminder emails or SMS are sent to participants with surveys due for completion each Monday at 08:00 am. For interviewer-administered tools, a data collector contacts participants when a survey or diary is due. Participants have 7 days to complete assigned tools before they expire. Up to three SMS, email and phone reminders prompt participants to complete baseline and follow-up surveys for interviewer-administered surveys. Individual reminders are not provided for daily diaries.

Figure 2
Figure 2

Overview of standardised quantitative data collection tools and scheduling for a 12-month period*. *As recruitment was extended to include additional recruitment targets—the following up period was extended to a maximum of 24 months. EOI, expression of interest.

All participants complete a key people form during the baseline interview, allowing data collectors to target eligible individuals for recruitment. Participants can nominate a maximum of 50 key people all together, but a maximum of eight per participant are selected for attempted recruitment (layers 1 and 2). If the participant gives permission and contact details for more than eight key people, a key people with the most in-person contact, are prioritised for recruitment.

Participants then complete a baseline survey about demographics, impacts of COVID-19, baseline behaviours (including social, health and lifestyle factors) before the pandemic, and attitudes to, knowledge and uptake of COVID-19-related mitigation strategies. A baseline prospective daily diary is then completed online on days 1–14 after recruitment to collect information on participant’s health, isolation/quarantine status, mood and detailed data on their contacts on the previous day. For participants who complete the baseline diaries with the assistance of a data collector, instead of daily interviews, the diaries are completed across two interviews, with data collected retrospectively for the previous 7 days.

For participants who report testing COVID-19 positive or being a close contact in the 7 days before baseline (group 1), a retrospective diary is administered with interviewer assistance to establish a timeline of COVID-19 events and capture experiences of quarantine, isolation and adoption of public health directions.

Follow-up data collection

Follow-up commences 28 days after recruitment; all participants receive individualised links via email or SMS, or a phone call from a data collector, to complete a follow-up survey. The follow-up surveys collect the same content as the baseline surveys, but cover the previous 4 weeks. Follow-up surveys also ask participants about face-to-face and digital contact with key people in the previous 4 weeks and allow them to nominate new key people.

Participants are invited to complete four follow-up diaries in a month scheduled randomly for two weekdays and two weekend days to capture data on COVID-19 testing, COVID-related symptoms, being a ‘close contact’ in the previous 7 days, and information on mood and details of people with whom they interacted ‘yesterday’. The follow-up diaries are designed to assess social interactions, cooperation with government restrictions, and COVID-19-related health, and enable timely identification of COVID-19 diagnoses or close contacts and trigger a manual assignment of a COVID-19 event-based dairy (described below). After 12 months, all participants receive a message at the start of their next follow-up survey and follow-up diary congratulating them on their participation and informing them that the study is continuing. If they complete these tools, they are automatically assigned to another 12 months of follow-up surveys and diaries.

COVID-19 event-based diaries

If participants reported that they had tested positive for COVID-19 or are identified as a close contact in any of the monthly follow-up surveys or diaries, they are invited to complete an event-based diary to collect information on testing experience, health status, symptoms, disease severity and ability to complete their 7 days of isolation or quarantine. It also collects detailed data on personal interactions in the period starting 2 days before symptoms developed or they tested positive (whichever came first).

Snapshot surveys

To inform ongoing changes in Victorian Government policy during the pandemic, we design (on request, within 10 business days) and deploy ad hoc cross-sectional snapshot surveys to collect more in-depth data on participants’ opinions, behaviours and attitudes to new government policies and COVID-19 mitigation strategies. Distinct from the 24-month follow-up cohort schedule, snap-short surveys are deployed on an ad-hoc basis. All cohort participants are invited to complete a snapshot survey, self-completed and in English, within 7 days; meanwhile, bilingual data collectors administer 15 phone surveys in AMD.

Data collection tools

Data collection tools, their rationales and key domains are described below:

  • EOI/screen (see online supplemental file 3A): publicly available form to register interest in the study, assess study eligibility and key target recruitment group membership, collect contact details and preferences for data collector call-back.

  • Key people form (see online supplemental file 3B): collects data on key people to inform snowball recruitment, social network mapping and analysis of COVID-19 infection spread and social network influence on behaviours and attitudes. Based on previous social network analysis forms.38

  • Baseline retrospective daily diary (see online supplemental file 3C): collects data from participants recently diagnosed with COVID-19 and/or notified as a close contact in the previous 7 days. This interviewer-administered survey targets the timing and sequence of events surrounding COVID-19 transmission over the previous 14 days, including interactions with healthcare services and the Victorian Government COVID-19 contact tracing team, living arrangements, and isolation or quarantine. Data collected includes testing and diagnosis, potential exposure, and symptomatic period.

  • Baseline survey (see online supplemental file 3D): collects data (within 7 days of recruitment) on demographics; health and well-being; healthcare utilisation; COVID-related health and attitudes; vaccination attitude, uptake and barriers; and knowledge of and attitude to public health measures and restrictions. Questions on residence type, tenure and unpaid care and responsibilities follow the 2016 Census of Population and Housing.39 Occupation and industry questions follow the Australian and New Zealand Standard Industrial Classification, 2006.40 Financial hardship questions (eg, missing meals) follow the Household Expenditure Survey and Survey of Income and Housing 2009–2010. Social connectedness questions (eg, frequency of visiting friends) follow Dias et al.41 Long-term illness, age and disability questions follow the Australian Longitudinal Study on Women’s Health.42 Mental health was assessed by the Generalised Anxiety Disorder 7-item (GAD-7)43 and Personal Well-being Index-Adult.44 Questions about confidence in government agencies follow the 2019 Canterbury Well-being Survey.45

  • Baseline prospective daily diary (see online supplemental file 3E): collects data via self-administered online surveys every day for 14 days after recruitment and consent. Each diary asks about health (adapted from FluTracking),46 isolation/quarantine status, mood and personal interactions on the previous day. Data collected for each contact named includes details about the relationship, age and gender, location where contact occurred (inside/outside), purpose and duration of contact, and if physical contact occurred. If the participant cannot name all contacts due to high number, confidentiality or preference, they are asked to estimate the number of additional contacts per location.

  • Follow-up survey (see online supplemental file 3F): collects data every 4 weeks, starting from week 5. This survey includes the same domains as the baseline survey but targets current circumstances and changes in the previous 4 weeks to enable assessment of COVID-19 impacts and behaviours and attitudes.

  • Follow-up daily diary (see online supplemental file 3G): collects data for 2 weekdays and two weekend days every 4 weeks (average 1 day/week), starting from week 5. In addition to asking about contacts on the previous day, the follow-up diary elicits information on health, isolation and quarantine status in the previous 7 days. The 7-day recall enables detection of participants with new COVID-19 events, including diagnosis and notification as a close contact, and establish a timeline of related events. If new COVID-19 events are detected and confirmed with the participant (case or close contact), then the participant will be invited to complete a COVID-19 event-based diary.

  • COVID-19 event-based diary (see online supplemental file 3H): collects data from participants diagnosed with COVID-19 and/or notified as a close contact of a case during the follow-up period. They are manually assigned an event-based diary scheduled for 7 days after their date of diagnosis or notification of being a household contact. The diary captures participants’ health status and recent COVID-19 transmission or exposure information, including interaction with healthcare services and the Victorian Department of Health, living arrangements, and isolation or quarantine. Data collected includes testing and diagnosis, potential exposure, and symptomatic period.

  • Snapshot surveys (see online supplemental file 4A-F): collects data from participants at key time points in the epidemic to assess behaviours and attitudes to COVID-19 topics and government policies. Topics include behaviours over Summer 2021–2022, incentives and barriers to vaccination, concerns about children returning to school, influence of potential cessation of the Victorian pandemic declaration, impacts of long COVID, and COVID-19 testing, prevention and response in schools.


Participants are reimbursed monthly for their efforts with electronic gift vouchers redeemable at major retailers. Initially, participants were reimbursed $A35 for the baseline survey and $15 if at least 10 (of 14) baseline prospective daily diaries were completed. For each month of follow-up, participants received $2.50 per follow-up daily diary and $25 per follow-up survey completed. Participants who test positive for COVID-19 or are a notified close contact are invited to complete an event-based diary each day for 14 days ($15). This was simplified in December 2020 to $50 for all recruitment and baseline data collection, $35 each month for completion if any follow-up was completed in that month (minimum one follow-up diary) and $15 for COVID-19 event-based diaries. If a participant is retained for 12 months, and completes a baseline and at least one follow-up survey a month, they are reimbursed $470. AMD-speaking participants are offered more flexible reimbursement methods (bank transfer or a mailed visa debit card) to overcome cultural and linguistic issues with electronic gift cards.

Data collection and management

To facilitate collection of social network data, we use NetCollect (V.2.1.94, SNA Toolbox), a purpose-built online data-capture platform.38 The software and data are hosted on the Burnet Institute’s local servers. NetCollect automatically sends survey links via email or SMS according to each participants’ data collection schedule, starting from date of consent. A data management plan and data dictionaries were developed and shared with all study collaborators. Quantitative data preparation, cleaning and analyses are conducted using R V. Data cleaning and analysis code is stored in Git for version control. Survey and network data are automatically extracted every fortnight via an application programming interface. To ensure timely identified of new COVID-19 cases and close contacts across the following period, NetCollect was programmed to notify Slack (a data communication platform) of notifications from survey responses. Slack prompts a data collector to contact the participant and invite them to complete retrospective diaries.

Data preparation for social network analysis

NetCollect offers data matching algorithms to identify and eliminate duplicate contact nominations within a person’s social networks. This conflict resolution process involves reviewing all study participants, key people and daily contacts for similarities in name and other characteristics and identifying probable matches according to specific rules. From this, Optimise and Swinburne University of Technology Social Network Research Lab study researchers review and verify matches manually through a separate algorithm. Multiple nominations of one individual are combined into a single record that contains all network information. Data analytics capacity is currently being integrated into NetCollect to support social network exploration and visualisation without data export to third-party software.

Data analysis and key outcomes

Each month the study executive identifies a topic for reporting, which informs the selection of key outcomes of interest. The topic is often related to a critical issue affecting the community and/or a government decision, such as a testing uptake, and acceptance of public health restrictions or a new vaccine roll-out. These topics inform the qualitative interviews and CEG discussions.

Data from the longitudinal surveys and diaries are analysed with respect to six focus areas:

  • Uptake of COVID-19 risk mitigation strategies including isolation, quarantine, vaccines, mask wearing, physically distancing.

  • Knowledge of COVID-19 restrictions and confidence in government decision-making.

  • Average number of contacts with key people per day and in different settings.

  • Changes in work and finances due to COVID-19 pandemic restrictions.

  • Changes in lifestyle and social engagement due to COVID-19.

  • Changes in physical and mental health due to COVID-19.

For monthly reporting, a specific relevant topic from the focus areas is selected and we report on key outcomes from each month:

  • What proportions of people are adopting risk mitigation strategies and are they experiencing any unintended health/financial/well-being consequences?

  • Do sociodemographic covariates influence adoption of risk mitigation strategies and experience of unintended health/financial/well-being consequences?

  • Does adoption of risk mitigation strategies and experience of unintended health/financial/well-being consequences vary over time?

Ordinal, nominal and binary data are summarised using frequencies and proportions for serial cross-sectional data. χ2 tests assess dependencies between survey responses for key outcomes and demographic variables, including gender, age group, employment status, healthcare worker status, if they have children (specifically in relation to vaccine uptake), country of birth, language spoken at home and household income. Continuous outcomes are assessed using mean, median and quantiles. T-tests and Wilcoxon tests are used to detect differences between demographic groups. Composite variables are formed as appropriate and any standard scales (ie, GAD-7 and Personal Well-being Index) are assessed using standard methodology.43 44 Missing data are assessed for causes (ie, missing completely at random, missing at random and missing not at random) and handled using multiple imputation or full information direct maximum likelihood if appropriate.

MPNet V.1.0448 is used for the statistical analysis of social network data using exponential random graph models and auto-logistic actor attribute models. This approach is used to consider whether individual mental health, vaccination attitudes and other characteristics are linked to specific network substructures in which individuals are embedded.

Community engagement groups

Study population and recruitment

To augment the longitudinal data, the CEGs provide interpretation of the cohort findings, generate new research topics/questions and assist in developing recommendations in response to these findings for government reports. The initial CEG comprised representatives of populations prioritised in the Optimise cohort (not participants): healthcare workers, international students, older people, people with chronic disease, young people, people who have had COVID-19, people living in regional Victoria and people living in crisis accommodation.

In September 2021, as additional target groups were added to the cohort, a CALD CEG was recruited to better represent the needs of multicultural (including Afghan, Fijian and Pasifika, Indian and South Asian) communities. Recruitment for both CEGs occurred through community leaders, representatives of community organisations and referrals through exiting organisational research networks.

CEG data collection tools and key measures

CEG teleconferences are held monthly with up to 10 participants per meeting. The topic under discussion is informed by the key issue identified for reporting in the monthly report provided to government (for more detail on topic guides see online supplemental file 6). A draft of the monthly Optimise report is provided to the CEG a week in advance of the meeting with the meeting agenda.

Each CEG meeting lasts approximately 90 min. Participants give their perceptions of the implications of the monthly report findings for their communities and their recommendations for government messaging or pandemic response.

CEG members receive a stipend of $112.50/meeting for their participation (including preparation time), paid as a digital gift voucher.

Data collection and management

Each CEG meeting is audio-recorded, detailed notes are taken and key quotations are transcribed by study researchers. Identifying information is redacted or concealed with pseudonyms. The digital records are stored on a password-protected La Trobe University network drive accessible only to study researchers.

Data analysis and key outcomes

CEG meeting data is analysed using framework thematic analysis, and summary notes of the discussion are circulated to members for approval. The CEG findings are then incorporated into the monthly Optimise report provided to the Victorian Government. Outcomes include:

  • Reflections on the monthly report findings based on personal experience and community insights.

  • Perceived implications of the findings for their communities.

  • Recommendations for government messaging or pandemic response.

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