Thousands of peaceful protesters demonstrated in Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike in infections as the omicron variant sweeps across Europe.

The marchers — some with placards reading “free zone,” “I've had my fair dose” and “enough is enough” — came to protest the government’s strong advice to get vaccinated. They also included Belgian health care workers who will have a three-month window in which to get vaccinated against the virus beginning Jan. 1 or risk losing their jobs.

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Protestors march during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Thousands of peaceful protesters demonstrated in Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike in infections as the omicron variant sweeps across Europe.

A protestor holds a sign during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Also Sunday, the Brussels-based European Commission agreed with Pfizer-BioNTech to accelerate the delivery of vaccines starting in a few weeks. The pharmaceutical giant will deliver an additional 20 million vaccine doses from January to March to the European Union's 27 nations.

Protestors wave coloured balloons at a police line during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

In a Brussels protest last month, several hundred people started pelting police, smashing cars and setting garbage bins ablaze. Police responded with tear gas and water cannons.

A protestor holds the German flag upside down in front of a police line during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

A protestor holds the German flag upside down in front of a police line during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors carry a giant unicorn during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. Sign at right reads 'No to obligatory vaccinations.' (AP PhotoOlivier Matthys)

Protestors carry a giant unicorn during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. Sign at right reads 'No to obligatory vaccinations.' (AP PhotoOlivier Matthys)

Protestors march during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. Sign at left reads 'Stay away from our children', and sign at right reads 'Freedom from injection'. (AP PhotoOlivier Matthys)

Protestors march during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. Sign at left reads 'Stay away from our children', and sign at right reads 'Freedom from injection'. (AP PhotoOlivier Matthys)

A protestor holds a score card that reads 'Pfizer-1, Belgium-0' during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

A protestor holds a score card that reads 'Pfizer-1, Belgium-0' during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors prepare to march with signs that read 'Free Zone' during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors prepare to march with signs that read 'Free Zone' during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors march with signs that read 'Free Zone' during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors march with signs that read 'Free Zone' during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors march with signs against the use of QR codes during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors march with signs against the use of QR codes during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors carry an Australian flag during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors carry an Australian flag during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors march with signs during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. Sign at right reads 'Don't touch the children.' (AP PhotoOlivier Matthys)

Protestors march with signs during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. Sign at right reads 'Don't touch the children.' (AP PhotoOlivier Matthys)

Protestors look at at objects which have been tossed toward a police line during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors look at at objects which have been tossed toward a police line during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors look at a scooter which has been tossed toward a police line during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors look at a scooter which has been tossed toward a police line during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

A strong police presence and widespread preventive controls were deployed for the march, given how previous protests had descended into violence. But only 13 arrests were made for “rebellion and possession of prohibited articles," according to police spokesperson Ilse Van de Keere.

Protestors march during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors march during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Also Sunday, the Brussels-based European Commission agreed with Pfizer-BioNTech to accelerate the delivery of vaccines starting in a few weeks. The pharmaceutical giant will deliver an additional 20 million vaccine doses from January to March to the European Union's 27 nations.

The Belgian protest comes one day after similar protests in other European capitals including Paris and London. Nations across Europe are reimposing tougher measures to stem a new wave of COVID-19 infections spurred by the highly transmissible omicron variant, with the Netherlands leading the way by imposing a nationwide lockdown.

The World Health Organization reported this weekend that the omicron variant has been detected in 89 countries, and variant cases are doubling every 1.5 to 3 days in places with community transmission.

A protestor holds a sign during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

A protestor holds a sign during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

In a Brussels protest last month, several hundred people started pelting police, smashing cars and setting garbage bins ablaze. Police responded with tear gas and water cannons.

Follow all AP stories on the pandemic at https://apnews.com/hub/coronavirus-pandemic.

Protestors wave coloured balloons at a police line during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors wave coloured balloons at a police line during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

A protestor holds the German flag upside down in front of a police line during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

A protestor holds the German flag upside down in front of a police line during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors carry a giant unicorn during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. Sign at right reads 'No to obligatory vaccinations.' (AP PhotoOlivier Matthys)

Protestors carry a giant unicorn during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. Sign at right reads 'No to obligatory vaccinations.' (AP PhotoOlivier Matthys)

Protestors march during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. Sign at left reads 'Stay away from our children', and sign at right reads 'Freedom from injection'. (AP PhotoOlivier Matthys)

Protestors march during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. Sign at left reads 'Stay away from our children', and sign at right reads 'Freedom from injection'. (AP PhotoOlivier Matthys)

A protestor holds a score card that reads 'Pfizer-1, Belgium-0' during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

A protestor holds a score card that reads 'Pfizer-1, Belgium-0' during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors prepare to march with signs that read 'Free Zone' during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors prepare to march with signs that read 'Free Zone' during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors march with signs that read 'Free Zone' during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors march with signs that read 'Free Zone' during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors march with signs against the use of QR codes during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors march with signs against the use of QR codes during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors carry an Australian flag during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors carry an Australian flag during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors march with signs during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. Sign at right reads 'Don't touch the children.' (AP PhotoOlivier Matthys)

Protestors march with signs during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. Sign at right reads 'Don't touch the children.' (AP PhotoOlivier Matthys)

Protestors look at at objects which have been tossed toward a police line during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors look at at objects which have been tossed toward a police line during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors look at a scooter which has been tossed toward a police line during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)

Protestors look at a scooter which has been tossed toward a police line during a demonstration against COVID-19 measures in Brussels, Sunday, Dec. 19, 2021. Thousands of protesters demonstrated through central Brussels on Sunday for a third time against reinforced COVID-19 restrictions imposed by the Belgian government to counter a spike infections and the emergence of the worrying omicron variant. (AP PhotoOlivier Matthys)