The armed forces are supporting the NHS in various parts of the UK as new data shows hospital staff absences due to Covid have risen 59% in a week.

More than 1,000 personnel have been made available to support the rollout of the vaccine in England, Scotland and Wales.

It came as a system-wide major incident was declared in Northamptonshire by health, public and emergency service leaders due to Covid-19.

Northamptonshire Local Resilience Forum, which is made up of NHS organisations, local authorities, Northamptonshire Fire and Rescue Service and Northamptonshire Police, issued the alert due to “rising demand on services and staffing levels”.

Chair of the forum, chief fire officer Darren Dovey, said: “Declaring this incident is a necessary step to make sure we are able to share resources where necessary which is increasingly important as more staff need to self-isolate.”

Meanwhile, NHS England data shows 39,142 NHS staff at hospital trusts in England were absent for Covid-19 reasons on January 2, up 59% on the previous week (24,632) and more than three times the number at the start of December (12,508).

The figures suggest one in 25 (4% of) NHS staff working in acute hospital trusts are off sick or self-isolating due to Covid.

This 4% is based on NHS Digital monthly workforce data for September for acute trusts (the most recent available).

The latest data shows in north-west England, 7,338 NHS staff at hospital trusts were absent due to Covid-19 on January 2, up 85% week-on-week from 3,966, while in north-east England and Yorkshire there were 8,788 absences, more than double the number a week earlier (4,179).

In London, absences were up 4% week-on-week, from 4,580 to 4,765.

Overall, there were 82,384 NHS staff at hospital trusts in England who were absent for all sickness reasons on January 2, including self-isolation and mental health reasons, up 21% on the previous week (68,082) and up 37% from the start of December (60,136).

NHS national medical director Professor Stephen Powis said rising Covid-19 cases were “piling even more pressure” on hospital trust workers.

He said: “Omicron means more patients to treat and fewer staff to treat them.

“In fact, around 10,000 more colleagues across the NHS were absent each day last week compared with the previous seven days and almost half of all absences are now down to Covid.

“While we don’t know the full scale of the potential impact this new strain will have, it’s clear it spreads more easily and, as a result, Covid cases in hospitals are the highest they’ve been since February last year – piling even more pressure on hard-working staff.

“Those staff are stepping up as they always do; answering a quarter more 111 calls last week than the week before, dealing with an increasing number of ambulance call-outs, and working closely with colleagues in social care to get people out of hospital safely.”

Patricia Marquis, the Royal College of Nursing’s director for England, said nurses found themselves “spread thinner and thinner, but they can’t keep spinning plates indefinitely… this situation is simply not safe.”

According to the Health Service Journal (HSJ), staff absences across the entire NHS, including mental health trusts and other areas, for any reason including Covid-19, may be as high as 120,000.

To help fill the gap there were around 1,800 military personnel committed to assist with 15 open Covid-19 Military Aid to Civilian Authority (MACA) requests, as of Friday.

In total, there are around 9,300 armed forces available on standby.

Over 740 personnel are supporting NHS England with the rollout of the booster.

In Scotland, 121 personnel are supporting the Scottish Government, with a further 100 made available last month.

Speaking to Sky News earlier, Dr Chaand Nagpaul, council chairman of the BMA, said “we have never known this level of staff absence before”.

He added: “Every winter of course, the NHS has additional pressures, but I don’t think anyone who’s worked in the NHS has experienced this level of absence of their colleagues and we’re feeling it in very real time because doctors and nurses and healthcare workers are having to cover for their absent colleagues – that’s adding additional, exceptional strain.”

Number 10 insisted Boris Johnson still sees no need for further Covid restrictions in England despite rising staff absences.

A spokesman said ministers would ensure the health service had the support it needed, adding that the Covid booster jab programme meant there was not the same level of pressure on intensive care units seen in previous waves.

“The Prime Minister has been clear on controls. Plan B is balanced and proportionate to respond to the Omicron variant. It is continuing to help reduce its spread. But the important thing is the booster programme and the effectiveness it has in stopping the disease,” the spokesman said.

He added: “The military have helped out throughout the pandemic and they will do so again.

“We know that staff absences are contributing to the pressure the NHS is currently facing. Of course we will continue to take appropriate measures to ensure the NHS has the support they need.”

The UK Health Security Agency said its latest data shows boosters continue to help older adults, as around three months after getting their third jab, protection against needing to be admitted to hospital remained at about 90%.

With just two vaccine doses, protection against severe disease drops to around 70% after three months and to 50% after six months for those aged 65 and over, it said.

The Joint Committee on Vaccination and Immunisation (JCVI) said there was no need to introduce a fourth jab for the most vulnerable – care home residents and those aged over 80.

It said priority should be given to rolling out first booster doses to all age groups, and urged unvaccinated people to come forward for their first two doses as soon as possible.

Professor Wei Shen Lim, the JCVI’s chair of Covid-19 immunisation, said: “The current data show the booster dose is continuing to provide high levels of protection against severe disease, even for the most vulnerable older age groups.

“For this reason, the committee has concluded there is no immediate need to introduce a second booster dose, though this will continue to be reviewed.

“The data is highly encouraging and emphasises the value of a booster jab. With Omicron continuing to spread widely, I encourage everyone to come forwards for their booster dose, or if unvaccinated, for their first two doses, to increase their protection against serious illness.”