Linda Bauld, professor of public health at the University of Edinburgh, said many countries had a policy to only admit fully vaccinated children aged 12 and over – but stressed this age group was not able to receive a second vaccination dose in Scotland and the rest of the UK.
She called on officials to allow an option for teenagers to be given a second vaccination.
Advice from the Joint Committee on Vaccination and Immunisation (JCVI) is for teenagers to receive just one dose of the vaccine, due to concerns over a small number of cases of myocarditis – heart inflammation – which is more likely to occur after the second dose of a vaccine.
According to travel rules for some countries, including India and Canada, youngsters aged 12 and above need to have had two doses of a recognised vaccine before they are able to enter the country, with no option to test instead.
In some places, non-vaccinated teenagers could quarantine for a number of days on arrival. However, this will not be practical for the majority of travellers.
Prof Bauld said members of the public had contacted her looking for clarification on how they could travel abroad with their older children.
She said: “Teenagers won't be able to travel to many countries without the second dose. There are a number of countries that are requiring double vaccination even for 12 and up.
"People are starting to wake up to this fact and it's because they're looking ahead to the Christmas period.
"For a number of places that Brits normally go – eg Spain – it's OK, because they're allowing a recent negative test as an alternative to if you travel with children, but other countries, you need to have had both doses and that includes the teenagers.”
Prof Bauld, who was born in Edinburgh, but grew up in the Canadian province of British Columbia, said she was unable to take her own teenage daughter to visit family in Canada due to the rules.
She said: “For example, I could go to Canada at Christmas to see my parents – I haven't seen them for more than two years – my 19-year-old son is double vaccinated, so no problem, but my 16 year old won't be able to get in.
"Unless the JCVI sorts this out, we're an international outlier in not giving teenagers two doses.
"The JCVI gives that advice, but they’re looking only at the health advice and that the myocarditis after the second vaccine is more of a risk – but they’re not thinking about people visiting their grandparents.
"I think if they made it optional and you could do it with that [travel] in mind, the uptake may not be huge, but there would be families who would want to take up that offer.”
In most countries in the European Union, as well as other nations including the US, those aged 12 and above are eligible to receive two doses of vaccination.
The Scottish Government refused to comment, but instead referred to the UK Government’s advice for travelling overseas.