Europe’s drug regulator said a booster shot of the Pfizer-BioNTech vaccine could be given to healthy adults.

The European Medicines Agency also said that extra doses of the Moderna and Pfizer-BioNTech vaccines could be given to people with underlying health conditions as early as 28 days after a second dose.

Help! I’m Traveling to Europe. All the Requirements Are a Dizzying Mess.

For three confused but vaccinated travelers, our columnist tries to make sense of the new rules of entry into the European Union.

AstraZeneca Vaccine Carries Slightly Higher Risk of Bleeding Disorders, Study Shows

But the research, involving 2.53 million adults in Scotland, found that the vaccine’s benefits outweighed the small risks.