Ms. Lembersky has also had luck with Italian-language resources like Salute Lazio, which has a map of pharmacies that conduct virus tests in the region of Lazio, as well as MedInAction, where users can book testing “house calls” throughout Milan and Rome.

Meanwhile, the travel medicine company AmbiMed maps out — and allows users to book — coronavirus tests throughout The Boot.

Certain U.S. Embassy websites can also be useful, but the information is by no means uniform, and travelers may need to click around. The website for Spain, for example, has a seven-page document in English with testing locations organized by region, while the website for Switzerland directs users to another site, with a list of testing sites by Swiss canton. The website also offers English-language links for the Swiss Department of Public Health.

Regardless of where your research lands you, be sure to book tests in advance, to be administered no more than three days before the return flight. (And starting in November, one day before flying for those unvaccinated Americans.) Triple-check that the final results contain the information required by the Centers for Disease Control and Prevention.

Whereas many E.U. countries are allowing residents to be tested for free, visitors will likely have to pay somewhere in the range of $25 to $100 per test, with antigen tests generally less expensive than P.C.R. tests. France, for example, is charging foreigners 29 to 49 euros (around $34 to $57).

Weigh the pros and cons of “home” or self-tests.

Most major airline websites now include information about how passengers can order F.D.A.-approved, in-home tests before their flights. Some, like American Airlines, are also offering discounts on certain brands, like Qured.

What to Know About Covid-19 Booster Shots

The F.D.A. authorized booster shots for a select group of people who received their second doses of the Pfizer-BioNTech vaccine at least six months before. That group includes: vaccine recipients who are 65 or older or who live in long-term care facilities; adults who are at high risk of severe Covid-19 because of an underlying medical condition; health care workers and others whose jobs put them at risk. People with weakened immune systems are eligible for a third dose of either Pfizer or Moderna four weeks after the second shot.

The C.D.C. has said the conditions that qualify a person for a booster shot include: hypertension and heart disease; diabetes or obesity; cancer or blood disorders; weakened immune system; chronic lung, kidney or liver disease; dementia and certain disabilities. Pregnant women and current and former smokers are also eligible.

The F.D.A. authorized boosters for workers whose jobs put them at high risk of exposure to potentially infectious people. The C.D.C. says that group includes: emergency medical workers; education workers; food and agriculture workers; manufacturing workers; corrections workers; U.S. Postal Service workers; public transit workers; grocery store workers.

For now, it is not recommended. Pfizer vaccine recipients are advised to get a Pfizer booster shot, and Moderna and Johnson & Johnson recipients should wait until booster doses from those manufacturers are approved. ​​The F.D.A. is planning to allow Americans to receive a different vaccine as a booster from the one they initially received. The “mix and match” approach could be approved once boosters for Moderna and Johnson & Johnson recipients are authorized.

Yes. The C.D.C. says the Covid vaccine may be administered without regard to the timing of other vaccines, and many pharmacy sites are allowing people to schedule a flu shot at the same time as a booster dose.

Reflecting on a recent trip to France, a Times reader named Allison wrote me to say she believed that buying self-tests through United’s Travel-Ready Center would have been a better move than what she encountered:

“We had to make an appointment with a lab and then drive over an hour each way,” she wrote. “The labs are closed on weekends; with an early-morning flight on Tuesday, we had to get tests on Monday. The tests cost $75 each and while the results were emailed to our phones, the results were in French and we did not receive them until late Monday evening.”