Syringes are prepared for doses of the Pfizer COVID-19 vaccine at a clinic in Los Angeles, California, on April 9.

A version of this story appeared in the April 14 edition of CNN’s Coronavirus: Fact vs. Fiction newsletter. Sign up here to receive the need-to-know headlines every weekday.

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Meanwhile, J&J has paused its vaccine rollout in Europe, as the European Medicines Agency (EMA) said it was closely monitoring developments around the shot in the US. EMA confirmed a “possible link” between the AstraZeneca Covid-19 vaccine and the same combination of blood clots and low platelet counts last week, but it stopped short of advising countries to limit its use.

The US has provided limited shipments of AstraZeneca’s vaccine – which is not yet authorized for use in the United States – to Mexico and Canada, but US Secretary of State Antony Blinken has said it won’t share shots more broadly until the country is “more confident” in its own supplies.

The US is the biggest financial donor to the global vaccine-sharing scheme COVAX, but the country has been tight-fisted with the actual vaccines it has in huge supply, while many others have none at all. Three-quarters of the world’s vaccines actually administered have been in just 10 nations, which together account for under half the world’s population.

“The world’s wealthiest nations have locked up much of the near-term supply. At the current rate vaccines are being administered, 92 of the world’s poorest countries won’t vaccinate 60% of their populations until 2023 or later,” wrote Dr. Krishna Udayakumar and Dr. Mark McClellan, health experts at Duke.

The report laid out a three-part plan in which the US should increase funding for COVAX, make excess doses available through the same scheme and create bilateral programs modeled on the President’s Emergency Plan for AIDS Relief – or PEPFAR – to provide shots and support to countries in need. It could also provide the support and materials for countries to produce safe and effective vaccines on their own.

The AstraZeneca vaccine, which the US has shared, has been paused in many age groups in Europe after regulators said the vaccine was possibly linked to dozens of rare but serious blood clotting events, some of them fatal. The US suspended use of the Johnson & Johnson vaccine on Tuesday after reports of the same rare clotting event in six people. The incidence remains extremely rare, at around one in a million.

It seemed nothing short of a miracle when it became clear that scientists had developed several effective vaccines against Covid-19 in less than a year. But announcements last week from European Union and British drug regulators finding a possible link between AstraZeneca’s Covid-19 shot and a rare blood clot condition have been a real low point in the pandemic.

YOU ASKED. WE ANSWERED.

Q. Do my kids need to be vaccinated before going to summer camp?

A. Of the vaccines authorized for use in the United States, both the Pfizer-BioNTech and Moderna shots give about 95% protection against symptomatic Covid-19, and both are virtually 100% effective against severe illness. In their clinical trials, no one who was vaccinated died from Covid-19.

The bigger worry is that the J&J pause could deliver a serious psychological blow to confidence in vaccines generally. But it’s important to remember these events are extremely rare. Out of nearly 7 million people who’ve received the J&J vaccine, there have been reports of just six cases of people experiencing cerebral venous sinus thrombosis in combination with low levels of blood platelets, the US Centers for Disease Control and the US Food and Drug Administration announced Tuesday. One of those people died.

Dr. Arnold Monto, acting chair of an FDA vaccine advisory committee, wants to remind people that the other two vaccines being used in the US, made by Pfizer and Moderna, are designed differently, and have not been linked to this rare blood clot event that authorities are investigating in the J&J shot, as well as the AstraZeneca shot used widely in Europe. Here’s what else to know.

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WHAT’S IMPORTANT TODAY

Keeping middle seats empty on airplanes can significantly reduce Covid-19 exposure

Leaving the seats vacant on airplanes can reduce a passenger’s risk of being exposed to the coronavirus by 23% to 57%, according to a study published Wednesday by the US Centers for Disease Control and Prevention.

Researchers used laboratory models to simulate how much exposure to virus particles could be reduced when middle seats are kept vacant in an aircraft cabin. The models were based on the spread of bacteriophage aerosols used as a surrogate to estimate the airborne spread of the coronavirus. Bacteriophages are viruses that can infect bacteria.

The analysis did not measure the impact of wearing masks, which is currently required on flights, but the researchers noted that some virus aerosol can be emitted from an infectious masked passenger and so distancing could still be useful.

Denmark drops AstraZeneca from its vaccination program

Denmark is the first country in Europe to remove the AstraZeneca Covid-19 shot from its vaccination program, following announcements last week from medicines regulators in the European Union and UK confirming a possible link between the shot and rare but serious blood clotting events.

The UK has limited the use of the vaccine to people aged 30 and over, while other European nations have taken a more cautious approach, only offering the shot to people in much older age groups. Younger adults appear to be experiencing the blood clotting events in higher numbers. The European Medicines Agency (EMA), however, did not advise any change in the way the shot is used, saying the cases were very rare and that the benefits still outweigh the risks.

“We are basically in agreement with EMA’s assessment regarding the AstraZeneca vaccine,” said Søren Brostrøm, Director General of the Danish Health Authority, adding the shot wasn’t needed because the country had already reached “an advanced point” in its vaccine rollout.

“If Denmark were in a completely different situation and in the midst of a violent third outbreak, for example, and a healthcare system under pressure – and if we had not reached such an advanced point in our rollout of the vaccines – then I would not hesitate to use the vaccine, even if there were rare but severe complications associated with using it.”

1 in 5 Americans will ‘likely never’ choose to get a Covid-19 vaccine

The US, along with the rest of the world, is banking on widespread vaccination to dig itself out of the pandemic. But the latest numbers from a Monmouth University national poll about the vaccination suggest vaccine hesitancy will be a major hurdle to achieving that.

More than half of people polled (51%) reported that they already had at least one shot of the vaccine. Another 14% said they plan to get one of the vaccines as soon as they can. Another 12% said they are waiting and seeing whether to get the vaccine. But more than 1 in 5 Americans (21%) said they will “likely never” get the vaccine. Chris Cillizza breaks down what we know about this group of people, including what their political leanings have to do with it.

New Zealand and Australia were Covid success stories. Why are they behind on vaccine rollouts?

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“You get vaccinated to protect yourself, but if enough people get vaccinated, the virus can’t circulate as much, not as many mutations will develop, and we won’t have to worry about the variants either.” — Dr. Sanjay Gupta, CNN’s Chief Medical Correspondent