Though rates of increasing the risk of blood clots for different birth controls vary, the ones that do range from 2-6x. The FDA estimates that in US out of every 10 thousand women using combination oral contraceptives or birth control pills 3 to 9 will develop blood clots each year while for comparison the same rate for women who are not pregnant and do not take COCs is 1 to 5 which is interesting considering the age range of the six cases.
https://www.fda.gov/drugs/drug-safety-and-availability/fda-d...
That said research is beginning to understand the mechanism of these rare blood clots in connection to adenovirus vector meds and since it is so rare it's hard to get a precise number but other studies predict an excess increase of severe blood clots in the range of 1 in every 500 thousand to million patients.
https://www.sciencedirect.com/science/article/pii/S000649712...
Do we have any data on the total number of women 18-38 who received this vaccine? It may actually be fairly low given we may have selection bias to give these vaccines to an older population.
The outcome may simply be to recommend that members in this demographic avoid this particular vaccine until further analysis is done.