Residents are being urged to use an under-capacity hospital if they want to ensure its long-term security.
Braintree Community Hospital, in Chadwick Drive, is currently running at half-capacity, despite being praised by inspectors in a report published this month.
But NHS bosses dismissed suggestions GPs had a financial incentive to send patients to other hospitals.
Serco is pulling out of its hospital management contract in December, warning it expects to post large financial losses.
About 100 concerned residents packed into Braintree Town Hall on Tuesday for the annual general meeting of the Friends of Braintree Community Hospital group.
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