ORLANDO, FLORIDA, UNITED STATES – 2021/04/10: Johnson & Johnson COVID-19 vial and box seen at a vaccination site. Doses of the Johnson & Johnson vaccine are given throughout the state of Florida, although a small number of patients have experienced side effects, including blood clots. (Photo by Paul Hennessy / SOPA Images / LightRocket via Getty Images)

SOPA pictures | LightRakete | Getty Images

Johnson & Johnson and AstraZeneca are exploring early on whether potential modifications to their Covid-19 vaccines could reduce or eliminate the risk of rare but serious blood clots related to the syringes.

The problem of blood clotting, which some scientists refer to as vaccine-induced immune thrombotic thrombocytopenia, or VITT, has been linked to both shots. Scientists have found evidence of how the clots form, raising hope for a possible overhaul of the shots, a person familiar with the matter told CNBC.

The Wall Street Journal reported the news on Tuesday.

In a statement to CNBC, J&J said it supports “continuous research and analysis as we work with medical experts and global health authorities”.

“Johnson & Johnson remains committed to ending this deadly pandemic as quickly as possible and we continue to believe in the positive benefit-risk profile of our vaccine,” the company said.

AstraZeneca said it was “working actively with regulators and the scientific community to understand these extremely rare blood clotting events, including information to promote early diagnosis and intervention and appropriate treatment.”

The Food and Drug Administration announced in April that it was adding a warning label to J & J’s Covid vaccine, citing the bleeding disorder as a rare side effect.

On Monday, the FDA said it was adding another warning to the J&J label stating the shot was linked to a serious but rare autoimmune disease called Guillain-Barre Syndrome.

According to the CDC, about 100 preliminary reports of Guillain-Barre were discovered after receiving 12.8 million doses of the J&J vaccine. The cases reported after receiving the J&J syringe mostly occurred around two weeks after vaccination and mostly in men, many of whom were 50 years of age and older, according to the CDC. The data available does not show a similar pattern with the Pfizer or Moderna vaccine, the agency said.

The FDA and CDC asked states on April 13 to temporarily discontinue use of the J&J vaccine “out of caution” while investigating six women, ages 18 to 48, who had combined cerebral venous sinus thrombosis, or CVST low platelets developed within about two weeks of receiving the shot.

They recommended resuming vaccination 10 days later after the CDC found that the benefits of the vaccinations outweigh their risks.

Tuesday’s Journal report noted that modification of the vaccines could require changes in property rights or regulatory approvals.