as long as there is a risk, you should always be aware and informed. a risk of very serious harm, including death, does exist, though it is very small: about one in 55,000 for the first dose .
we now have a much better understanding of how to diagnose and treat clotting due to covid-19 vaccines, called vaccine-induced thrombotic thrombocytopenia, or vitt (also sometimes called vaccine-induced prothrombotic immune thrombocytopenia, or vipit) when it does occur. death rates among people who experience vitt have been estimated at 20 to 50 per cent , but may be improving as knowledge increases. the public health agency of canada monitors all adverse events following covid-19 vaccination.
advertisement
getting the second dose of any two-step vaccine is very important. that’s what cements the memory of the immune response. we know from clinical trials that the first dose does not prevent all infections. it prevents death from infection. the second dose boosts the immune response to almost completely protect you from getting any infection. that second dose also greatly reduces your ability to carry or spread the virus at all.
in terms of timing, evidence is still emerging, but the best guidance regarding astrazeneca is that a 12- to 20-week gap between first and second doses is ideal, much as it is with most vaccines.
the risk of a blood clot after a second dose is about one in 600,000 , which is one-tenth the risk of clotting after an initial dose. if you were comfortable getting the first dose, you should feel good about going ahead and continuing to help the community bring the pandemic closer to its end. in addition, knowing the symptoms associated with the vaccine-related clots allows for timely recognition and immediate treatment.
advertisement
canada’s national advisory committee on immunization recommends that for a second dose, you should stay with a vaccine made with the same technology “platform ” as the first. if you first got astrazeneca, which is a form of viral vector vaccine, it’s recommended that you get it again. if it is not available, johnson and johnson is another viral vector vaccine.
advertisement
the symptoms of vitt are well documented and include the following, which occur four or more days after vaccination:
it is important to seek prompt medical care in these cases. it is also important to note that minor fever, headache, fatigue and pain at the site of the vaccination are common with all vaccines in the first one or two days and are not causes for concern.
clotting events are still so rare that it is very difficult to identify any particular risk factors. although it appears that a slightly higher number of women have experienced clotting , the number of cases isn’t large enough to accurately assess whether sex might affect risk.
the astrazeneca vaccine is not recommended for people who have had a previous case of heparin-induced thrombocytopenia , or of rare cerebral venous sinus thrombosis clots. a family history of clotting does not appear to be relevant to vaccine risks since the mechanisms are completely different.
advertisement