Welsh ministers say they cannot rule out imposing another firebreak lockdown early in 2021 if Covid-19 starts spreading quickly again at Christmas.
Economy Minister Ken Skates urged people to stick to the rules during Wales' two-week lockdown from Friday.
Scientific advisers say it is possible the reproduction (R) rate could drop from 1.4 to 0.8 over that period.
However, the impact of the firebreak will not be known until some time after the lockdown has ended.
The R rate is the number of people that one infected person will pass the virus to, on average.
Mr Skates told the Welsh Government's coronavirus news briefing on Tuesday that lowering the R rate to that extent "would, in itself, buy us enough time, give us the headroom, to get through to Christmas and the new year".
"But of course we could not rule out the possibility of introducing another firebreak if over the Christmas period transmission rates increase dramatically," he said.
A report by the Technical Advisory Cell (TAC), which advises Welsh ministers on coronavirus, estimates that a two to three-week lockdown "should act to reduce R below 1" but that "multiple" such lockdowns may be needed.
"Over a fortnight's 'break', two weeks of growth could be exchanged for two weeks of decay in transmission, assuming good adherence to measures, and no additional increase in contacts before or after the break," the paper says.
"If this were as strict and well-adhered to as the restrictions in late May, this could put the epidemic back by approximately 28 days or more."
The report, published on Monday, adds that if rules and behaviour then returned to how they were before the firebreak "there would be a return to exponential growth, but from a significantly lower level than would have been the case without the break".
But it also warns "multiple" firebreaks "might be necessary to maintain low levels of incidence" of the virus.
Senedd backs call to eliminate Covid
A majority of Senedd politicians backed the firebreak lockdown in a vote on Tuesday evening - 37 for to 16 against.
The vote's text included a call from Plaid Cymru - which won three amendments to the motion - for a strategy based on eliminating the virus. Conservative members were among those voting against the main motion.
At the debate Tory Senedd group leader Paul Davies said the Welsh Tories had an "open mind", but that the Welsh Government had failed to justify its new measures.
First Minister Mark Drakeford accused the Conservative Party in the Senedd of placing "themselves in opposition to all the expert advice we have available to us".
Plaid Cymru leader Adam Price said that the government "has no option" and that the lockdown should have been introduced earlier.
But continual lockdowns were not an answer, he said, adding: "We have to use this time to reflect on what's gone wrong and what can be put right."
Local lockdowns 'could not turn tide'
Earlier, answering First Minister's Questions at the Senedd, Mr Drakeford said the current local lockdowns could not "turn back the tide" of Covid-19 quickly enough.
Currently about 2.3 million people in Wales are living under local lockdown rules - 15 of the 22 council areas plus Bangor and Llanelli - where coronavirus infection rates are at their highest.
Paul Davies said the Welsh Government should publish more local data to show how the disease is spreading on a "community-to-community basis".
But the first minister said a "national effort" was needed.
"It's very easy indeed to justify it [the firebreak] because while the efforts that have been made by people in those local lockdown areas are succeeding, they cannot succeed far and fast enough to turn back the tide of coronavirus as it is currently accelerating across Wales," he said.
Mr Davies' comments came prior to the release of more detailed local information by Public Health Wales on Tuesday afternoon.
What happens from 9 November?
Opening the debate, Health Minister Vaughan Gething said Covid-19 policies that will come into force after the firebreak will be set out "in the coming days".
Local lockdowns, covering the vast majority of Wales's population, are likely to be replaced by a new national regime when the firebreak finishes.
Monday's TAC report advises ministers to follow a "new, simpler, national approach to behaviours and restrictions".
"Simpler messaging and regulations are expected to be easier to understand and comply with," it says.
"Some existing restrictions may be removed if they are shown to be less effective or more harmful than originally expected, such as the local authority travel boundary restrictions [preventing people entering or leaving local lockdown areas without a reasonable excuse, such as for work]."
But the report warns that there would need to be "sustainable changes in behaviour in many areas of life" to keep the R number "as near to one as possible".
"Across the government we are now looking to work to agree arrangements that will be needed in the future to secure the gains made from the firebreak and we will set those out in the coming days," Mr Gething said.
Ministers have relied on projections of a worst case scenario, prepared by Swansea University, which say there could be as many as 6,000 Covid-19 deaths in Wales by March.