Millions of people caught covid over the Christmas period.
As Omicron washed over the country in December, more than four million people in England tested positive for the virus.
While the Omicron variant of Covid-19 causes milder symptoms than other strains, particularly in people who are vaccinated, it can still cause severe illness in some people.
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The high transmissibility of Omicron means that a large number of infections can eventually overwhelm hospitals by reducing staff numbers and taking up capacity desperately needed for treating other patients.
Some hospitals were forced to cancel non-urgent surgery and appointments in December and January due to rapidly rising infections.
The record-breaking number of infections in the Omicron wave meant millions weren't eligible to get their booster vaccine, leading health experts to issue a warning, the Mirror reports.
People who test positive for coronavirus have to wait 28 days after a positive test, or after symptoms started, before getting a booster under guidance from the Joint Committee on Vaccination and Immunisation (JCVI).
More than 10 million people have had their booster since they were made available to every adult on December 15, but 6.3 million people have missed their booster by six weeks or more, according to new NHS data.
The NHS sent over 5 million reminder texts just last week, reminding people to come forward and get vaccinated.
If you are vaccinated you are 85% less likely to end up in hospital than unvaccinated people, according to the latest data from the UK Health Security Agency (UKHSA).
Experts are warning people to act now to protect health and wave goodbye to Covid-19.
NHS National Medical Director, Professor Stephen Powis, said: "Everyone would like to see the back of covid and as things begin to return to normal it is important we don't lose sight of what will protect you from the virus.
"If you were one of the millions of people who tested positive in December and were unable to get your booster, it is time to come forward for that vital vaccination 28 days on from catching covid.
"More than six million people are overdue their booster by at least six weeks, and while some had to delay because of a coronavirus infection it is still absolutely crucial that people get their booster in order to increase their protection to reinfection and the dangers of long covid.
"The evidence is clear, vaccination provides the best protection for you and your loved ones against coronavirus, so I urge anyone yet to come forward for their booster – or their first or second dose – to check where their nearest site is online and get protected now."
As cases soared before Christmas, Professor Iain Buchan, dean of Liverpool University’s Institute of Population Health, said: "There are still quite a few people who are leaving themselves open to a life-threatening fever instead of a mild cold.
"Get vaccinated if you haven't been. Get a booster, regardless of any prior infection. Just get it when you're called and come forward, get boosted."
More than 37 million people in the UK have had their booster jab, but in Liverpool, fewer than half of people aged 18 and over have had a third dose of the vaccine, compared with an uptake of around 73% and 68% for doses one and two.
Dr Fiona Lemmens, an Aintree GP and chair of Liverpool CCG, previously told the ECHO: "I do think I get it, you know, we were all told, 'You get your second dose and that's you sorted'.
"So you think that the third dose is not quite so important, and until very recently, there wasn't that much in the news - covid rates weren't particularly high - and so people were putting it off.
"Now, with Omicron and with the huge transmissibility of Omicron, it's just ripping through the population.
"It is much, much more important now to get your third dose.
"We know that protection from two doses of vaccine is good, but not good enough, and it's that booster dose that is really giving the protection against Omicron."
People eligible for a vaccine can turn up to walk-in centres without an appointment.
Booked slots are also available at chemists, GP practices and community sites.
As thousands get their first jabs, doctors are keen to stress that people won't be judged for getting vaccinated now if they haven't already.
To book a vaccination appointment online, you can visit the NHS booking site and select a time and place that suits you.
If you want to get your booster, click the green "book now" button where you'll be asked for your NHS number.
Don't fret if you don't have it to hand. Instead, just fill out your personal details or book a slot by calling 119.
Invitations sent by text come from NHSvaccine and include a link to the NHS website, allowing eligible people to book an appointment at a suitable site.
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