Researchers are looking into whether certain vaccines against COVID-19 affect women differently than men, after the majority of patients who reported developing blood clots after taking an AstraZeneca and Johnson & Johnson jab were female.

As of 4th April, the European Medicines Agency received 169 reports of a particular kind of blood clot, called cerebral venous sinus thrombosis, CVST, in patients who took the AstraZeneca jab as well as 53 cases of splanchnic vein thrombosis, which is the clotting in the veins of the abdomen. 

Most of these patients were women under the age of 60. However, it is important to note that in both Germany and Britain for example, more women took the AstraZeneca vaccine than men. Additionally, these cases are very rare, considering that 34 million people took the jab in Europe.

However, as immunologist Prof Neil Mabbott told Euronews, it is too early to know whether the vaccine is, “in very, very rare instances” triggering blood clots in some patients.

Blood clotting was listed as a side-effect of the COVID-19 vaccine by the European Medicines Agency but the risk is exceptionally rare. According to the UK’s health authorities, a clot can occur in one in every 100,000 people who take the jab.

Malta’s Superintendent of Public Health Charmaine Gauci echoed these sentiments, previously telling Lovin Malta that vaccines, like many medicines, have side effects.

In fact, Gauci added there is more risk of developing a blood clot from taking oral contraception.

Blood clot reports connected to Johnson & Johnson vaccine

Meanwhile, the Johnson & Johnson single-shot vaccine also faced suspension in the US and EU after reports of blood clotting in some patients.

Six people in the US developed a rare blood clotting condition after taking the jab. Every single patient affected was a woman. However, this is just a crumb of the 6.8 million who have received the vaccine in the US, and health officials are extremely weary of drawing conclusions on whether the patients’ sex played a role. 

That being said it is too early to rule out varying effects of the vaccine on women.

In one preliminary study that analysed data from the Central for Centers for Disease Control and Prevention, researchers found that women reported more acute reactions to inoculation than men, including headaches, fatigue and dizziness.

The CDC’s study looked at vaccination data in the US from December 2020 found that women received 61% of vaccine doses and made up 72% of side effects.

A possible explanation being explored is that estrogen can produce a stronger immune response, which heightens the impact of side effects.

In fact, in another 2013 study,  researchers found that women were more likely to suffer negative reactions to the 2009 swine flu pandemic vaccine compared to men, even though more men received vaccines. Women also made up 80% of anaphylactic reactions to vaccines in adults, according to a study on data from 1990 to 2016.

All in all, as infectious diseases Professor William Schaffner told Euronews, estrogen could play a role in impacting the way women experience vaccines, but the potential cultural and biological factors “really hasn’t been well-studied”.

Lovin Malta has reached out to the Health Ministry about the issue.

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