1. First assume independence, that CVST is unrelated to vaccination.
2. Take any two weeks, you can calculate the expected cases using population background rate because we assume independence.
3. The number is around 1 using Wikipedia data.
4. The observed case number 6 greatly exceeds the expected number based on independence assumption.
5. We conclude that with high probability that our independence assumption is wrong, i.e. there's correlation with high confidence.