Only 25 per cent of Morwell residents so far targeted by the Hazelwood Health study have agreed to participate in the large survey component of the project.
It has prompted the research team to urge residents to recognise the significance of the study for the region's future health.
"This means we have no health information for the remaining 75 per cent," study investigator Professor Judi Walker said.
The Adult Survey is the largest component of the study - an initiative which the community called for in response to concerns about the potential long-term health impacts of the 2014 Hazelwood mine fire.
"Over and above the analysis of the impacts of the mine fire, the findings will be vital to health planning for the region's future," Professor Walker said.
The Monash-led research team has so far invited 4691 eligible adults in Morwell, including those who have moved away since the fire, to complete the Adult Survey, as well as a further 1300 adults in Sale, which has been selected as the study's 'comparison town'.
This week a fourth Morwell area, bound by McDonald Street, Princes Drive, Churchill Road and Hourigan Road, will be sent Adult Survey invitation packs.
Professor Walker said it was critical residents understood this was their only opportunity to ensure any long-term health effects from the six-week fire event could be tracked and responded to.
"We understand residents are experiencing a level of survey fatigue following the fire with so many different fire-related activities underway," Professor Walker said.
"We know there are misconceptions about what this study might be about, but we want to reassure everyone that this is the only independent research that is monitoring the short and long-term health impacts of the smoke exposure.
"If people don't complete the survey, then we won't have the information needed to identify, understand and respond to any health impacts which may show up in the years to come."
Professor Walker said the research team had selected the Hunter Research Foundation, an experienced and respected survey-specialist organisation, to interview Adult Survey participants over the phone.
The study team plans to run stands at busy locations in Morwell, including Mid Valley, over the next few months and will provide paper-based surveys to anyone who prefers these over the online and telephone survey options.
The questionnaire takes about 30 minutes to complete and asks participants about their cardiovascular and respiratory health, and proximity to the mine fire.
The study also seeks permission to access some general health information such as hospital, ambulance and cancer registry records, but this does not include details of private conversations with doctors or test results.
The researchers need to collect health information from as many eligible adults as possible, whether old, young, well or unwell and regardless of whether they think they were impacted or not.
Professor Walker said a younger group of Morwell adults had not responded in high numbers to the survey but she insisted their support was essential.
"We know when people are younger and healthy, in particular, they may not worry much about their long-term health, but they might be more concerned later in life."
If invited residents have already opted not to complete the survey it is not too late to 'opt back in'.
They can do so by following the instructions on their invitation pack or calling 1800 985 899 or visiting http://hazelwoodhealthystudy.org.au/research-areas/adult-survey/adult-survey-faqs/ for more information.
Professor Walker also urged any community groups who were keen to know more about the Adult Survey, to make contact, as a study team member may be able to attend a meeting and provide more information.
Those who choose to participate will be compensated for their time with a $20 Latrobe City gift card, redeemable at about 85 local businesses.