It is now law again to wear a mask in shops and other indoor public places in Jersey.
Islanders are also being asked to work from home where possible, to limit the spread of the Omicron Covid variant.
Adults will now only be considered 'fully vaccinated' if they have had three jabs.
Ministers announced the measures on 15 December, but said they would take effect on 4 January.
The latest coronavirus numbers for Jersey are expected to be published later.
Figures have not been updated over the bank holiday weekend, but more than 400 people a day were testing positive for the virus in the final few days of 2021.
Passengers arriving in Jersey who are not full-vaccinated can provide evidence of a negative PCR taken within 72 hours or have a free PCR test on arrival and isolate until a negative result.
Being recently recovered from Covid-19 is no longer accepted as an alternative to being full-vaccinated under the island's revised Safer Travel Policy.
All passengers will be subject to the same requirements regardless of travel history unless they have visited a UK Red List country.
“Earlier this month we announced new travel recommendations that would be implemented from 4 January following the emerging risks faced as a result of the Omicron variant. At this time, we announced that the definition of Fully Vaccinated would be updated in light of the evidence that only two doses of the vaccine offers reduced protection against the variant, particularly due to waning immunity if your second dose was administered some months ago.
“We will now also be making some further changes with effect from 4 January. This includes changing the age a passenger must complete a pre departure travel form from 11 to 12, this is so that it is in line with the age of vaccination eligibility.
“Additionally, those passengers arriving from outside of the CTA will not be treated any differently to those travelling from within the CTA. All passengers will be required to have a PCR test at the border and isolate until their day 0 negative test result unless they meet the updated definition of Fully Vaccinated or have completed a pre-departure PCR test.” - Chief Minister Senator John Le Fondre.
On 30 December the isolation period for people with Covid-19 was cut from 10 to 7 days for those who are fully vaccinated or aged under 12, providing:
* Two negative Lateral Flow Tests (LFTs) have been registered via the online portal at Day 6 and Day 7, at least 24 hours between each test have been symptom-free for 48 hours.
People with the virus who are not fully vaccinated must continue to quarantine for ten days.
Direct contacts are no longer required to take a PCR test. They have to take LFTs for ten days.
"If you are identified as a Direct Contact, you will continue to be notified by the COVID Safe team by text message or email. If you test positive on an LFT, you will need to attend for a confirmatory PCR test by booking online or calling the Coronavirus helpline. If you are symptomatic, you should still book a PCR test online." - Government of Jersey
As children return to school for the new term, they have been asked to take a home Covid test beforehand.
Staff in schools and childcare/early years settings have been offered a PCR test before the reopening of nurseries, schools and colleges.
The Vaccination Centre at Fort Regent is currently operating as a walk-in clinic, meaning people can get a first, second or booster dose without an appointment.