Speaking at the first government Covid briefing of the year, the prime minister said it was likely many countries would seek evidence of booster jabs.
Johnson’s comments came as the government continued to resist pressure to impose further Covid restrictions in England to guard against additional cases of the new Omicron variant.
Scotland and Wales have toughened their Covid measures in an attempt to mitigate the Omicron wave.
Addressing the press and public at Downing Street on Tuesday (4 December), Johnson urged those already fully vaccinated to get their boosters, and those yet to receive any vaccine doses to come forward and get jabbed.
“It is already the case that to travel to some countries, you need a booster to be considered fully vaccinated," said Johnson, adding it was likely that "within weeks" this would increasingly "become the norm".
The Sun’s Harry Cole pressed the PM further on vaccine certification, specifically on when a third jab or booster will become a pre-requisite for fully vaccinated status.
Johnson said no date had been set, but stressed people would have "plenty of time" to get their shots before any such change is made.
He added it would be "very much to people’s advantage" to get booster jabs if they want to travel, with other countries likely to change their rules in the same way.
The prime minister also said that while the NHS will be placed on a "war footing" to tackle Omicron, he would be recommending to cabinet that no further restrictions or measures are introduced in England and that the current Plan B would continue.
