Several nations have issued new guidelines over the use of AstraZeneca's COVID-19 vaccine after the European Union's medical regulator announced a link between the vaccine and rare, possibly fatal blood clots.

Britain, where the vaccine was developed jointly by the British-Swedish drugmaker and scientists at the University of Oxford, says it will offer alternatives for adults under 30. Oxford researchers have also suspended a clinical trial of the AstraZeneca vaccine involving young children and teenagers as British drug regulators conduct a safety review of the two-shot regimen.

Reuters says Spain and the Philippines will limit the vaccine to people older than 60, while The Washington Post says Italy has issued similar guidelines.

The European Medicines Agency said Wednesday the blood clots should be listed as a very rare side effect of the AstraZeneca vaccine, but continued to emphasize that its overall benefits outweigh any risks. Rare blood clots have been associated with the deaths of at least 14 people across Europe.

AstraZeneca has been the key vaccine in Britain's exceptionally speedy inoculation campaign, which has outpaced significantly the vaccination rates in the rest of Europe. But the vaccine has had a troubled rollout across the world, initially because of a lack of information from its late-stage clinical trials on its effect on older people, which has slowed vaccination efforts throughout Europe. Many nations stopped administering the AstraZeneca vaccine after reports first surfaced of the blood clotting incidents.

The vaccine is critical also to Europe's immunization campaign and crucial in the global strategy to supply vaccines to poorer countries. The vaccine is cheaper and easier to use than rival vaccines from Pfizer-BioNTech and Moderna.

In the United States, the Centers for Disease Control and Prevention says the B.1.1.7 variant of the coronavirus first detected in Britain last December is now the dominant variant in the country. The CDC had predicted back in January that the British variant, which is far more contagious and deadly than the original version, would become the dominant one in the United States by March.

"The virus still has a hold on us, infecting people and putting them in harm's way. We need to remain vigilant," said CDC Director Dr. Rochelle Walensky on Wednesday during a White House briefing.

The United States recently surpassed 30 million total new cases, including 559,116 deaths, the most of any country in either category, according to Johns Hopkins Coronavirus Resource Center.

New Zealand Prime Minister Jacinda Ardern announced Thursday that her country is suspending travel from India beginning Sunday due to a surge of coronavirus cases among travelers from that country. New Zealand has 23 new positive COVID-19 cases in quarantine, 17 of them from India. The ban will remain in effect until April 28, and will include New Zealanders returning from India.

India has nearly 13 million total coronavirus cases, third behind the United States and Brazil, and is undergoing a second wave of new infections as it races to vaccinate its 1.3 billion people. The country posted a single-day record 126,789 new cases on Wednesday.