"The risk of thrombosis is more frequent with contraceptives than with the vaccine".

Cases of thrombosis reported after vaccination with AstraZeneca are one in 300,000. "The risk of cerebral venous thrombosis is more frequent with contraceptives, which is 2%, and nobody stops taking contraceptives," says the head of the stroke unit at Vall d'Hebron Hospital, who also explains that behind women who have suffered thrombosis after taking contraceptives there is "an underlying coagulation problem".

The thromboses reported by AstraZeneca's vaccine - which they have named "vaccine-induced prothrombotic immune thrombocytopenia (VIPIT)" - resemble heparin-induced thrombosis, although it is, as with the vaccine, "a rare complication". "It is stated in the drug's data sheet, but it is not a reason not to use the drug or the vaccine," says Molina. "It is much more frequent with heparin - approximately every 80,000 cases - than with the vaccine, but it has been detected in clinical trials and is treated. The drug is not withdrawn because the benefits far outweigh the problem," he adds. He adds that the risk of thrombosis if you get covid is higher. "The combination of stroke and covid is one of the worst there is," he says. "These complications happen, and if you look at any drug's package leaflet you get scared, but it should be stated and documented for the information of patients," adds Molina, who insists that the benefit of the vaccine against the coronavirus is "much higher than the small percentage that may suffer thrombotic processes". "People are concerned about the contradictory information, and rightly so, but the message should be one of reassurance because this is part of normal clinical practice: all drugs and vaccines have side effects, they are evaluated and we move on," he explains.

Cerebral venous thrombosis is a very rare form of stroke, with three to four cases per year. VIPIT is an immunological reaction due to a side effect of a drug or vaccine. When the vaccine is administered, an autoimmune response is generated to protect against covid, but there are rare cases where a cross-response can also occur and antibodies are generated, which also act against the structure of platelets. "The platelets clump together and decrease in number, and thrombotic phenomena occur in unusual locations". These thrombi are located in abdominal and cerebral veins, which are rare locations.

If detected early, vaccine-induced autoimmune thrombocytopenia can be treated with immunoglobulins and thus stop the thrombotic process.

It is normal to have a mild headache 24 to 48 hours after vaccination, which will go away with painkillers. However, if the headache is very intense, does not let you sleep, does not go away with painkillers, is accompanied by vomiting and blurred vision, is worse lying in bed, is more intense in the morning than in the afternoon and is accompanied by other neurological signs, such as loss of vision, loss of strength in the arm or leg and epileptic seizures, then you should consult a doctor and have an assessment. These symptoms appear in the first two weeks after vaccination.

The head of the stroke unit at Vall d'Hebron says that "it is not exclusive" to women. "But women have a higher percentage of autoimmune responses, and the vaccine generates a response of antibodies that go against the structure of platelets, which is more frequent in autoimmune diseases, which are more frequent in women than in men. However, there is also a selection bias, Molina points out, as in recent months older people have mostly received the Pfizer vaccine and younger people the AstraZeneca vaccine.

Vaccination of people with autoimmune diseases, such as lupus or multiple sclerosis, is not contraindicated and they should not be at increased risk of induced thrombosis, Molina says. Nor should people with blood coagulation disorders be at increased risk of vaccine-induced thrombotic thrombocytopenia (VIPIT), "just as they are not at increased risk of heparin-induced thrombocytopenia".

Only people who have already suffered from heparin-induced thrombosis should proceed "with caution", as the triggering mechanism is very similar to that of vaccine-induced thrombosis, explains Carlos Molina. "It is the only case to be taken into account, but it is very carefully considered, as they are extraordinarily rare cases."

Molina says there is not enough data on cases of thrombosis with the second dose and he is in favour of administering it. "People who have already received the first dose should rest assured," he says.