Swiss voters have firmly backed the law behind the country’s COVID pass, according to projections following Sunday’s referendum after an unusually tense and hostile campaign.

Shortly after the polls closed at noon (1100 GMT), market researchers GFS Bern, who conducted the main polling throughout the campaign, projected that 63 percent of voters had backed the “yes” vote.

The law provides the legal basis for the so-called COVID certificate, indicating that a person has been vaccinated or has recovered from the disease.

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Opponents have said the certificate, which has been required since September for access to restaurants and other indoor spaces and activities, is creating an “apartheid” system.

As in much of Europe, Switzerland has seen growing anger over restrictions aimed at reining in the pandemic, and pressure to get vaccinated.

But in a country where referendums take place every few months in a climate of civility and measured debate, the soaring tensions around the vote came as a shock.

Police upped security around several politicians who have faced a flood of insults and even death threats.

In anticipation of protests at the results, police have fenced off the seat of government and parliament in Bern.

Observers warned that Sunday’s vote could exacerbate tensions, and even spark a violent backlash from the losing side.

The campaign saw repeated protests, often led by the so-called “Freiheitstrychler”, or “Freedom ringers” – men dressed in white shirts embroidered with edelweiss flowers and with two large cowbells suspended from a yoke resting on their shoulders.

Some of the demonstrations led to violent clashes with police, who used rubber bullets and tear gas to rein in the crowds.

The referendum came as the worrying new COVID-19 variant Omicron, first detected in southern Africa and classified as a variant of concern by the World Health Organization, has rattled countries and markets around the world.

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