We are traveling to Italy to board a cruise for a week and then Croatia in August/September. My 2 kids have been vaccinated and they are 9 and 12. We have flights booked to return home from Croatia on September 10, overnighting in London and flying back to Canada from London the next morning. It will have been 270 days since my kids had their second shot while we are in Croatia, on September 7. Does anyone have experience with this or think this will be a concern? We could probably get my daughter a third shot since her shots were a pediatric dose since it was before she turned 12, but third doses aren't approved for my son. Will we have trouble entering the country if his vaccine "expires" before we are planning to leave?