New mask mandates and other measures aimed at reducing the spread of the Omicron coronavirus subtype went into effect in England on Tuesday, as Prime Minister Boris Johnson considers expanding the COVID-19 booster program.

Face masks are now required on public transportation, as well as in stores, banks, and hair salons, as of Tuesday morning.

All overseas tourists must take a PCR test by the end of the second day after arrival and self-isolate until the results are available. This is in addition to the limitations imposed on arrivals from ten southern African nations, who must pass through hotel quarantine.

Britain has reported 11 cases of the Omicron variant so far, and while the government says this number will rise, it says it is important to slow its spread until more is known about the variant’s transmissibility and impact on vaccines.

“The measures taking effect today are proportionate and responsible, and will buy us time in the face of this new variant,” Johnson said in a statement.

“Not only will today’s steps help us slow down the variant’s spread, but they will help us protect each other and the gains we have all worked so hard for.”

Johnson has said the measures will be reviewed after three weeks, but added that the country’s vaccine rollout leaves it in a better situation than this time last year, when restrictions were introduced shortly before Christmas.

On Monday vaccine advisers gave the go ahead to a booster programme for all adults, and health minister Sajid Javid said there would be more details on how it would be implemented this week.

Booster shots are expected to help protect against severe disease even if Omicron is able to reduce vaccine efficacy.

“Based on everything we know, our vaccines and boosters remain our best line of defense,” Johnson said.