undefined

Johnson & Johnson's (JNJ) COVID-19 vaccine is possibly linked to reports of rare blood clots, and a warning will be added to the vaccine's information to include the rare side effect, according to the European Medicines Agency Tuesday.

The agency said in a statement it "concluded that these events should be listed as very rare side effects of the vaccine."

But the vaccine will continue to be used as the benefits outweigh the risks, the EMA said, noting that a clear cause or a trend in risk factors has not yet been identified.

No such cases have been reported in the European Union, where the company proactively halted the rollout and the regulatory body took a proactive approach based on experiences in the U.S., according to EMA executive director Emer Cooke.

J&J unpaused shipments to European countries Tuesday following the announcement.

Cooke noted that the EU's experience with the Oxford University/AstraZeneca (AZN) vaccine, which had similar issues and uses a similar platform, helped inform its decision ahead of the anticipated U.S. regulatory decision on Friday. The AstraZeneca vaccine has been limited in its use in many European countries as a result.

Dr. Sabine Straus, chair of the Pharmacovigilance Risk Assessment Committee, which advises the EMA, said the blood clots occurring following the J&J vaccine are less prevalent than those reported from AstraZeneca's vaccine.

The agency is requiring J&J's Janssen unit, which produced the vaccine, to further look into the data and conduct additional studies. Currently, evidence does not point to specific risk factors causing the blood clots — which mostly occurred in women under the age of 50.

The U.S. has reported six confirmed cases, with potentially two additional cases yet to be confirmed, of the more than 7 million J&J doses administered. The six cases largely occurred in women under the age of 50— that demographic accounts for just over 1 million of the administered doses, according to J&J.

Dr. Paul Offit, a top vaccine expert and director of the Vaccine Education Center at Children's Hospital of Philadelphia, told Yahoo Finance the warning is fair, but it does little to dispel fears and hesitancy of vaccines.

"What's upsetting to me in all this is we are not very good at explaining relative risk. We're afraid of dioxin and radon when we should be afraid of French fries," Offit said, noting that there are other drugs and daily activities that pose higher risks.

Another expert, Dr. Peter Hotez, said a better and more powerful message would be for the U.K., EU and U.S. regulatory bodies to provide a joint statement on the blood clots.

"One-off statements by regulatory authorities don't provide the level of reassurance that we need," said Hotez, dean for the National School of Tropical Medicine at Baylor College of Medicine.

Especially since similar reports about the AstraZeneca vaccine suggest a link between the rare side effects and the platforms used — adenovirus vectors. The Russian vaccine, Sputnik V, is also based on a similar technology, but no cases of clots have been reported yet.

Cooke told reporters Tuesday that while the review of Sputnik for use in Europe is still in early stages, the EMA will be "paying very close attention to this issue during the review of the Sputnik dossier. So far, we have not seen any reports ... of the information we have been able to review so far."

CDC decision

On Friday an advisory panel to the U.S. Centers for Disease Control and Prevention (CDC) will meet to evaluate the incidents of blood clots following the J&J shots. The CDC and U.S. Food and Drug Administration's pause on the vaccine is likely to end Friday, according to recent comments from Dr. Anthony Fauci.

Some experts are questioning the timing of Europe's decision, asking why EMA jumped ahead of U.S. regulatory authorities, particularly when EMA's decision was based on U.S. cases.

Dr. Arthur Caplan, a vaccine bioethicist and professor at NYU Langone, said the EMA will have to be very careful about how it words its warning, since it is still unclear if the vaccine is directly linked to the blood clots.

"Clearly it's an association, though very rare, but it hasn't been connected as a cause from vaccination," Caplan said.

Global impact

The broader impact of any labels and warnings on low-cost, easy-to-produce vaccines like AstraZeneca and J&J is already being felt.

"If the J&J was the first to come to be authorized, we would be having a different conversation," Offit said, adding, "We need a worldwide vaccine."

Though Pfizer (PFE)/ BioNTech (BNTX) and Moderna (MRNA) have also had rare reports of blood clots, details are unclear on specifics and the issue is still being studied. But since no regulatory action has been taken, the two entities are continuing to gain market share. The two also reportedly declined a show of industry support to address blood clots when approached by J&J.

Financial analysts anticipate the impact will be favorable to Pfizer and Moderna, with the two likely to take the lion's share of the global COVID-19 vaccine market — for countries that can afford them.

But experts worry curbing the pandemic may take longer if fewer countries have access to the mRNA vaccines and are hesitant about the adenovirus vector vaccines.

Offit said that ideally, the mRNA companies should be more willing to license their vaccines to major vaccine makers like the Serum Institute of India in order to ensure more vaccines are available.

Hotez noted that the cost of the vaccines is less of an issue than production.

"It's difficult to scale them. That's been the problem in vaccine equity, it's not so much the cost as it is availability," he said.

Pfizer and Moderna vaccines require two doses and need colder storage and have shorter shelf lives in refrigerators. By comparison, J&J is a single-dose vaccine that remains stable for months in normal refrigerator temperatures. Another key difference is J&J stating its vaccine would be produced and sold on a non-profit basis, whereas the other companies have said they intend to profit from the new technology.

But the biggest difference is J&J and AstraZeneca's platforms are much easier to produce, while Pfizer and Moderna are relying on newer technologies that haven't been scaled to a global degree before.

More from Anjalee:

• J&J vaccine pause remains, Oxford studies blood clots and COVID-19 vaccines

• China, Russia playing 'greater-than-expected' roles in global pandemic response

• Biden COVID-19 adviser: Vaccine news is great, but we still have a ways to go

Read the latest financial and business news from Yahoo Finance.

Follow Yahoo Finance on Twitter, Facebook, Instagram, Flipboard, SmartNews, LinkedIn, YouTube.

Follow Anjalee on Twitter @AnjKhem.