With the Omicron variant on the march, President Joe Biden has announced 500 million free rapid tests for Americans, increased support for hospitals under strain and a redoubling of vaccination and boosting efforts.

In a speech, Mr Biden detailed major changes to his Covid-19 winter plan, his hand forced by the arrival of the fast-spreading variant, whose properties are yet not fully understood by scientists.

The world is confronting a second straight Covid-19 holiday season as families and friends begin to gather. Scientists do not yet know for sure how serious the disease caused by Omicron can usually be, but they do know that vaccination should offer strong protections against severe illness and death.

A cornerstone of the plan is Mr Biden’s decision for the government to purchase 500 million coronavirus rapid tests for free shipment to Americans starting in January.

People will use a new website to order their tests, which will then be sent by US mail at no charge, the White House said.

It marks a major shift for Mr Biden, who earlier had called for many Americans to purchase the hard-to-find tests on their own and then seek reimbursement from their health insurance.

For the first time, the US government will send free Covid-19 tests directly to Americans, after more than a year of urging by public health experts.

Experts had criticised Mr Biden’s initial buy-first, get-paid-later approach as unwieldy and warned that the US would face another round of problems with testing at a critical time.

Testing advocates point to places like the UK and Germany, which have distributed billions of tests to the public and recommend people test themselves twice a week.

The federal government will also establish new testing sites and use the Defence Production Act to help manufacture more tests.

The first new federally supported testing site will open in New York this week. The new testing sites will add to 20,000 already available.

White House officials said they are working with Google so that people will be able to find them by searching “free Covid test near me.”

Still, Mr Biden’s testing surge would fall far short of the levels needed for all Americans to test at the recommended rate of twice weekly.

The US would need 2.3 billion tests per month for everyone 12 and older to do that, according to the non-rofit Kaiser Family Foundation. That is nearly five times the half-billion tests Biden will deploy.

Currently, the US can conduct about 600 million tests per month, with home tests accounting for about half, according to researchers from Arizona State University.

In another prong to Mr Biden’s amped-up plan, he is prepared to deploy an additional 1,000 troops with medical skills to assist hospitals buckling under the virus surge.

Additionally, he is immediately sending federal medical personnel to Michigan, Indiana, Wisconsin, Arizona, New Hampshire and Vermont. There are also plans to ready additional ventilators and protective equipment from the national stockpile, expanding hospital resources.

As a backstop, the Federal Emergency Management Agency will deploy hundreds of ambulances and paramedic teams so that if one hospital fills up, they can transport patients to open beds in other facilities. Ambulances are already headed to New York and Maine, and paramedic teams are going to New Hampshire, Vermont and Arizona.

But vaccination remains the main defence, since it can head off disease in the first place. The government will support multiple vaccination sites and provide hundreds of personnel to administer shots. New rules will make it easier for pharmacists to work across state lines to administer a broader range of shots.

For those who are already fully vaccinated, booster shots have been shown in lab tests to provide strong protection against Omicron.

Although reports of breakthrough cases abound, data show that vaccinated people who become infected are much less likely to suffer serious disease leading to hospitalisation or death. To the unvaccinated, Mr Biden plans to deliver a stern admonition that they are risking their lives and the lives of their loved ones.