Quarantine and testing may be back on the cards for British travellers who don't get a booster jab.
Official sources confirmed ministers are considering a change in regulations that means travellers entering the UK without a third "booster" dose of the vaccine would face quarantine and testing when they returned from overseas travel.
The Government updated official guidance earlier this month to say they were "reviewing the implications and requirements of boosters for international travel certification".
Part of this review included "looking at whether and how booster vaccinations could be included in the NHS Covid Pass for travel".
The change does not appear to be imminent but if it goes ahead the UK will follow in the footsteps of countries like Croatia, Austria and Israel who have imposed time limits on vaccination validity.
Travellers visiting Croatia and Austria must get a booster jab 365 and 360 days respectively after their second vaccination while Israel requires a third jab after just 180 days.
Paul Charles, chief executive of travel consultancy The PC Agency, told the Guardian other countries would probably follow suit.
"It's likely countries will continue to ensure we are fully jabbed. By fully jabbed that means being up to date. We are seeing countries starting to align," he said.
The booster jab is has been already been strongly recommended by the UK's Health Secretary Sajid Javid for those over 50 or who have a high risk of Covid-19.
According to recent NHS figures, more than 10 million people in the UK have received a booster, which Mr Javid said was crucial for protecting the elderly and vulnerable.
"I strongly urge everybody who is eligible for a Covid-19 booster or flu vaccine to take up the offer as soon as you can," he said.
According to London newspaper, the Evening Standard, the NHS will have sent 16 million invitations for a booster by next week.
Immunocompromised people can get a third dose of the vaccine in New Zealand. However, Kiwis keen on a top-up will have to wait for next year as officials work on a booster programme.
According to the Vaccine Alliance Aotearoa New Zealand-Ohu Kaupare Huaketo (VAANZ), trials are planned for the last quarter of the next year.