The US Centers for Disease Control and Prevention (CDC) has extended its no-sail order for passenger cruises to 31 October.
It is understood CDC chief Robert Redfield had hoped to have the order extended until mid-February.
However, it was earlier this week reported that an intervention by the White House resulted in the extension being shortened, in comparison to previous moves.
In effect, the new order means cruises of more than 250 passengers in US waters cannot resume until November at the earliest.
The order was enacted in March, and has been extended three times since then.
The latest extension brings the order in line with the self-imposed 31 October cruise halt agreed by Clia lines earlier this year.
CDC data records "at least" 3,689 Covid or "Covid-like" cases of illness on cruise ships in US waters from 1 March to 29 September, with 41 reported deaths, although the CDC said these figures were likely to be an underestimate.
The CDC said recent outbreaks onboard cruise ships were evidence cruising "continues to transmit and amplify" the spread of Covid-19, "even when ships sail at reduced passenger capacities".
It added this would "likely spread the infection into US communities if passenger operations were to resume prematurely".
"The challenges described in the no sail order highlight the need for further action before cruise ships can safely resume passenger operations in the United States," said the CDC.
"Recent passenger voyages in foreign countries continue to have outbreaks, despite cruise ship operators having extensive health and safety protocols to prevent the transmission of SARS-CoV-2 [Covid-19] on board and spread to communities where passengers disembark.
"When health and safety protocols were apparently observed, resuming passenger operations significantly burdened public health authorities by creating the need for additional testing, isolation of infected travellers, contact tracing, and quarantine of exposed people."
The CDC added: "The continued spread of the Covid-19 pandemic worldwide, risk of resurgence in countries that have suppressed transmission, ongoing concerns related to restarting of cruising internationally, and need for additional time to assess industry measures to control potential SARS-CoV-2 transmission on board cruise ships with passengers without burdening public health, support continuation of the no sail order at this time."
TTG is awaiting comment from Clia.