With new guidance following reports of rare blood clots, the global medical community is considering whether it’s possible, and safe, to administer two different vaccine candidates to the same person.    

This week the European Medicines Agency and the U.K.’s Medicines and Healthcare products Regulatory Agency both determined that there is a possible link between the AstraZeneca-University of Oxford vaccine and very rare cases of unusual blood clots with low blood platelets.

Neither the European nor the U.K. health regulators recommended age restrictions in using the vaccine. However, the U.K. regulator did note that the data suggested that there is a slightly higher incidence reported in the younger adult age groups and therefore advises that this evolving evidence should be taken into account when considering the use of the vaccine. 

The EMA similarly reiterated that the vaccine is safe and effective, but noted that use of the vaccine at a national level will also take into account the pandemic situation and vaccine availability in the individual countries.

Subsequently the U.K., various EU countries and other governments around the world have moved to recommend using alternative vaccines for younger people. 

Given the change in guidance, younger people are now asking the question: If I’ve already received one dose of the vaccine, should I come back for the second one?

Governments have different answers to this question. Health experts generally agree that the mixing and matching of the vaccines should be safe. But clinical trials are ongoing.

In contrast, France’s health regulator recommends that people under the age of 55 who have received their first dose of AstraZeneca should get Pfizer or Moderna for their second shot. It advises a gap of 12 weeks between these first and second shots in these instances. The regulator stated there is no reason to fear specific adverse events if you had the first AstraZeneca jab and then switch to an mRNA jab for the second.

Germany has followed a similar path. The German vaccine committee recommended that people under the age of 60 who had received one shot of the AstraZeneca jab should opt for a different vaccine for their second dose.

The Centers for Disease Control and Prevention maintains that the safety and efficacy of a mixed-product series have not been evaluated.

Several trials are underway to look at the effects of mixing vaccines. The U.K. launched a trial in February looking specifically at mixing the AstraZeneca-Oxford vaccine with the Pfizer-BioNtech shot. Findings are not expected to be available until the summer. Separately, trials are being held looking at a combination of the AstraZeneca-Oxford and the Russian Sputnik V vaccines.

Dr. Scott Gottlieb, who advised cruise lines on Covid protocols, told CNBC on Friday he believes a safe environment can be created on the ships.

Gottlieb’s comments came one day after Republican Florida Gov. Ron DeSantis said the state sued the Centers for Disease Control and Prevention, demanding the public health agency allow cruise lines to immediately resume sailing from the U.S. ports.

Gottlieb, who co-chaired an advisory panel for Norwegian Cruise Line Holdings and Royal Caribbean, said on “Squawk Box” the companies have sensible policies in place in preparation for when they’re allowed to begin operating after a Covid pause that’s lasted more than a year.

“They’ve committed to things like mandatory testing of passengers. Norwegian Cruise Line came out recently saying they’re going to require vaccination of all their passengers,” said Gottlieb, who served as Food and Drug Administration commissioner from 2017 to 2019 in the Trump administration.

Gottlieb also noted that social distancing would be possible on the ships, saying “these cruises are not going to operate at full capacity.”

“As you start to implement all these public health recommendations … you start to create an environment that could be quite safe,” he contended. “I believe you can create a safe bubble around that experience, especially when you’re comparing it to other vacation experiences where you can’t control the environment,” he added.

Cruise ships were hot spots for Covid outbreaks last year in the early days of the global health crisis, prompting the CDC to issue its no-sail order in mid-March 2020. While the CDC has issued some guidance for cruise lines under its conditional sailing order, the agency has yet to specify a date for operators to resume sailing from U.S. ports.

In response to CNBC’s request for comment on Gottlieb’s remarks, the CDC said via email that it’s “committed to working with the cruise industry and seaport partners to resume cruising following the phased approach outlined in the conditional sailing order. This goal aligns with the desire for resumption of passenger operations in the United States expressed by many major cruise ship operators and travelers, hopefully by mid-summer.”

However, the cruise industry is growing impatient, after companies raised billions in debt and issued new stock to fund operations while sailing revenues dried up. Late last month, a trade group called on the CDC to permit a phased-in restart in early July. Operators have said they’re seeing strong booking demand, suggesting people are starting to feel comfortable to return to cruises.

In a CNBC interview Wednesday, Carnival CEO Arnold Donald pointed to differences between restrictions in America and other countries across the world, where cruises have resumed in some places.

“A person today can fly from the U.S. to another country. Get on a cruise ship, and then come back to the U.S. whether they’re vaccinated or not,” Donald said on “Closing Bell.” “But here in the U.S., even if you’re vaccinated, at this point, you couldn’t get on a cruise ship.”

Donald complimented the Biden administration for its work on Covid vaccination distribution in the U.S., where roughly 20% of the population is fully vaccinated. He said he believes the cruise industry and CDC will be able to jointly reach an agreement on sailing.

“The administration has made huge progress with vaccinations and getting command of this thing,” Donald said. “We’re confident we can work together and arrive at something that would be a workable solution and hopefully we have sailings from the U.S. yet this summer.”

Royal Caribbean CEO Richard Fain told “CBS This Morning” on Thursday that he would like the cruise industry to be “treated in a very similar way to the airlines,” which have been allowed to fly. However, Fain is optimistic about the possible resumption of U.S. sailings in the second half of this year, citing President Joe Biden‘s goal for society to return to a semblance of normal by July 4.

— CNBC’s Katie Tsai contributed to this report.

Disclosure: Scott Gottlieb is a CNBC contributor and is a member of the boards of Pfizer, genetic testing start-up Tempus, health-care tech company Aetion Inc. and biotech company Illumina. He also serves as co-chair of Norwegian Cruise Line Holdings′ and Royal Caribbean’s “Healthy Sail Panel.”

Chinese regulators hit Alibaba with a 18.23 billion yuan ($2.8 billion) fine in its anti-monopoly investigation of the tech giant.

In a Saturday statement, China’s State Administration for Market Regulation accused Alibaba of abusing its market dominance.

Regulators opened a probe into the company’s monopolistic practices in December. The investigation’s main focus was a practice that forces merchants to choose one of two platforms, rather than being able to work with both.

The government said that “choose one” policy and others allowed Alibaba to bolster its position in the market and gain unfair competitive advantages.

“Alibaba accepts the penalty with sincerity and will ensure its compliance with determination,” Alibaba said in a statement. “To serve its responsibility to society, Alibaba will operate in accordance with the law with utmost diligence, continue to strengthen its compliance systems and build on growth through innovation.”

The company added it will hold a conference call on Monday at 8 a.m. Hong Kong time to discuss the fine.

The announcement is the latest development in China’s crackdown on its technology companies. Regulators have been increasingly concerned about the power of China’s tech giants, particularly those who operate in the financial sector.

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