Total deaths across Europe from Covid-19 are likely to exceed 2 million by March next year, the World Health Organization (WHO) has said, adding that the pandemic had become the number one cause of death in the region.

Reported deaths have risen to nearly 4,200 a day, double the number being recorded in September, the agency said, while cumulative reported deaths in the region, which includes the UK, have already surpassed 1.5 million.

Describing the situation as “very serious”, the WHO said it expected “high or extreme stress” on hospital beds in 25 of the region’s 53 countries, with intensive care units in 49 countries set to come under similar strain.

On current trends, the region’s cumulative death toll would surpass 2.2 million by 1 March, it said.

As Europe again becomes the centre of the pandemic, with tighter controls mainly on the unvaccinated and heated debate in several countries about making vaccination obligatory, Austria this week became the first west European country to re-enter lockdown since inoculation began earlier this year.

The increase in cases was being driven by the highly transmissible Delta variant which is now dominant across the region, the WHO said, fuelled by a widespread relaxation of preventive measures, such as mask wearing and physical distancing, since the summer.

With more and more people gathering indoors in the colder late-autumn weather, a large number still not vaccinated, and vaccine efficacy against severe forms of the disease waning, “many people are left vulnerable to the virus”.

Dr Hans Kluge, the WHO’s regional director for Europe, said it was essential that countries adopted a “vaccine plus” approach. “This means getting the standard doses of vaccine and taking a booster if offered,” he said, “but also incorporating preventive measures into our normal routines.”

In combination with the vaccines, Kluge said, wearing a mask, washing your hands, ventilating indoor spaces, keeping physical distance, and sneezing into your elbow were “simple, effective ways of gaining control over the virus”.

He added: “All of us have the opportunity and responsibility to help avert unnecessary tragedy and loss of life and limit further disruption to society and businesses over this winter season,” by avoiding “the last resort of lockdowns and school closures”.

The WHO said more than 1bn vaccine doses had been administered in the WHO European region and 53.5% of people had completed their inoculation programme, but added that the figure “hides wide differences between countries”, with some populations less than 10% vaccinated and others more than 80%.

The vaccines were “are a vital tool to prevent severe disease and death” and had saved hundreds of thousands of lives, it said, calling for governments to do more to increase coverage, including by working with behavioural and cultural scientists to understand individual and community reluctance.

But with evidence growing that the vaccines’ protection against infection and mild disease declined over time, it urged that booster doses “should be given to protect the most vulnerable, including the immunocompromised, as a priority”, as well as to the over-60s and heathcare workers as a precaution.

Data showed only 48% of people across the region wear a mask when they leave home, it said, estimating that 95% mask usage could prevent more than 160,000 deaths that could otherwise occur before 1 March.

“Today, the Covid-19 situation across Europe and central Asia is very serious,” Kluge said. “We face a challenging winter ahead, but … all of us – governments, health authorities, individuals – can take decisive action to stabilise the pandemic.”