LONDON—The euro slumped on Friday to near 16-month lows after Austria became the first country in western Europe to reimpose a full lockdown and Germany did not rule out doing the same. The single currency has been on the back foot all week, pressured by growing expectations that interest rates will be tightened faster elsewhere, particularly in the United States. The dollar was on track for a fourth straight week of gains against major rivals, capitalising on the euro’s woes. European Central Bank President Christine Lagarde doubled down on her cautious position on Friday, saying the ECB should not tighten policy as it could undermine recovery. Austria also said it will require all its citizens to be COVID-19 vaccinated by February, while Germany’s health minister cautioned lockdown restrictions could return there. “One thing is certain, if the whole of Europe had to go under lockdown once more, and depending on …