Many countries are expanding COVID-19 vaccine booster programs or shortening the gap between shots as governments scramble to shore up protection against the new Omicron variant which emerged a month ago in southern Africa and Hong Kong.

Studies have shown that an initial course of COVID-19 vaccines - typically given in two doses - may not be enough to halt infection from Omicron, but a booster shot may help.

The World Health Organization has recommended that only people with health issues or inactivated vaccine should get boosters.

Here are some of the options countries and regions are considering:

NORTH AMERICA

U.S. health regulators on Nov. 19 expanded eligibility for booster shots to all fully vaccinated adults.

The U.S. Centers for Disease Control and Prevention (CDC) took a more cautious stance on Nov. 30 than previously, when it said everyone over 18 should get a booster shot as Omicron's emergence emphasized the importance of vaccination.

Canada's National Advisory Committee on Immunization is recommending booster shots of an authorized mRNA vaccine to those who are moderately or severely immunocompromised.

EUROPE

The European Centre for Disease Prevention and Control (ECDC) on Nov. 24 recommended vaccine boosters for all adults, with priority for those over 40. Previously it had suggested the extra doses should be considered for frail older people and those with weakened immune systems.

The European Commission is recommending vaccinated people receive booster doses no more than six months after their initial shots, with a further three-month grace period for their COVID travel passes to be valid.

The EU's drugs regulator said on Dec. 9 that data supports vaccine boosters after three months.

These European countries are offering boosters to adults after they receive a full dose of a vaccine:

** Austria (soon to recommend for over-12s four months after second dose); Belgium (all over-18s); Britain (accelerated its program offering jabs to over-18s by end-Dec, third dose after three months); Czech Republic; Denmark (will cut booster shot interval to 4-1/2 months from six months for people aged 18-39, already in place for over-40s); France (delivered 12.5 million booster shots and was targeting 20 million by Christmas, cut the interval to four months vs five previously. Its regulator recommended on Dec. 24 administering boosters three months after first course); Germany (all over-18s; recommends booster after three months); Greece (three months after second vaccine shot or positive test, down from six months previously); Hungary; Ireland (all adults); Italy (so far for over-40s, will be made available to all over-18s); Malta (all over-12s); Netherlands (starting with over-60s, booster gap of three months); Norway; Poland; Russia; Romania (only Pfizer or Moderna boosters were approved); Serbia; Slovakia; Spain (Pfizer or Moderna booster shots for all inoculated with J&J); Sweden (will begin gradual rollout to all adults)

These European countries are offering boosters to people with weak immune systems, the elderly or vulnerable:

** Bulgaria; Finland (may expand to other Finns later, booster gap narrowed to 3 months); Lithuania; Portugal (to be offered to a quarter of its population by the end of January, including over 50s inoculated with J&J vaccine); Slovenia; Spain (expanded from over-60s to over-40s; Switzerland (new recommendation for people under 65 expected in the next few weeks)

AFRICA

A few African countries are offering boosters amid the continent's low inoculation rates - only 7.5% of Africa's population are fully vaccinated, according to WHO.

These African countries are offering boosters to adults after they receive a full dose of a vaccine:

** Egypt approved on Dec. 16 a booster shot for those who received their second shot at least six months ago. It had earlier approved boosters for the most vulnerable groups.

** Morocco, which has administered the most doses in Africa, started giving a third dose in October.

** Nigeria started to offer booster shots from Dec. 10 to those fully vaccinated.

** South Africa started offering booster shots of Johnson & Johnson's COVID-19 vaccine from Dec.24.

** Tunisia (5 months after second dose).

** Zambia started administering booster jabs as of Dec. 27 to over-18s, prioritizing health workers and later those with health conditions that made them vulnerable.

ASIA, MIDDLE EAST

** India will start giving booster doses for healthcare and frontline workers from Jan. 10 as cases of the Omicron variant are rising across the country.

** Kuwait will require incoming travelers to have the booster shot if more than nine months have passed since their vaccination

These countries are offering boosters to adults after they receive a full dose:

** Bahrain (Sputnik V, all over-18s at least six months after second dose); Cambodia (AstraZeneca); Indonesia (health workers only, wider population planned in 2022); Israel (all over-12s; health ministry recommended a fourth dose to over-60s and those who received a booster shot at least four months ago); Malaysia (over-18s; mandatory for over-60s, those vaccinated with Sinovac, and high-risk groups); Philippines (halved to three months the waiting time for a booster dose); Singapore (booster gap reduced to 5 months); South Korea (reduced the booster gap for all adults to three months from four-to-five); Taiwan (booster gap reduced to 5 months); Thailand (AstraZeneca or mRNA-type booster shots to people who were administered Sinovac brand, second dose after 3 months); Turkey; UAE (mandatory for people inoculated with Sinopharm vaccine).

These countries are offering boosters to people with weak immune systems, the elderly or vulnerable:

** Bhutan (over-65s and older, as well as priority groups such as health workers, sufferers from chronic medical problems among others); (China; Hong Kong; Japan (started administering boosters to health care workers in early Dec., will offer shots to elderly as of January, after 6 months from last dose vs 8 previously).

AUSTRALIA began administering Pfizer COVID booster shots in November to fully vaccinated adults. It cut the time interval for booster shots to five from six months.

LATIN & CENTRAL AMERICA

These countries are offering boosters to adults after they receive a full dose:

** Brazil; Panama (cut the rollout time for boosters to three from six months for over-16s); Uruguay (offers a Pfizer dose for those fully vaccinated with Sinovac).

These countries are offering boosters only to the immunosuppressed:

** Ecuador (boosters for general population planned from January 2022)

These are offering boosters to elderly, vulnerable and at-risk people:

** Chile; Brazil; Dominican Republic, El Salvador (elderly, health workers, people with underlying health conditions);

** Mexico plans to administer COVID-19 vaccine booster doses soon, beginning with elderly people.