LONDON (AP) — Prime Minister Boris Johnson says that Britain faces a “tidal wave” of infections from the omicron coronavirus variant and he has announced a huge increase in booster vaccinations to strengthen defenses against it.

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Johnson said in a televised statement Sunday that everyone age 18 and older will be offered a third shot of vaccine by the end of this month.

The previous target was the end of January.

He said cases of the highly transmissible variant are doubling every two to three days and “there is a tidal wave of omicron coming.”

Johnson announced a “national mission” to deliver booster vaccines at with pop-up vaccination centers and 7-day-a-week clinics.

Answers to 25 common COVID-19 vaccine questions

Vaccinations for COVID-19 began being administered in the U.S. on Dec. 14, 2020. The quick rollout came a little more than a year after the virus was first identified in November 2019. The impressive speed with which vaccines were developed has also left a lot of people with a lot of questions. The questions range from the practical—how will I get vaccinated?—to the scientific—how do these vaccines even work?

Keep reading to discover answers to 25 common COVID-19 vaccine questions.