4 Comments
User's avatar
⭠ Return to thread
Jami Gaither's avatar

From the Supplemental comments:

"We used two-month periods as our basic time interval for defining the sub-cohorts, but combined months 12 to18 for the Recovered cohort and omitted months 8 to 10 for the Vaccinated and the hybrid cohorts due to the small number of individuals."

And also:

"Typically, infection rates among recovered or vaccinated individuals are compared to the infection rate among unvaccinated-not-previously-infected persons. However, due to the high vaccination rate in Israel, the latter cohort is small and unrepresentative of the overall population; furthermore, the MoH database does not include complete information on such individuals. Therefore, we did not include unvaccinated-not-previously-infected individuals in the analysis."

Expand full comment
Jami Gaither's avatar

From the Data:

● Recovered: Previously infected individuals 90 or more days after confirmed infection who had never been vaccinated.

● Recovered then Vaccinated: Previously infected individuals who later were 7 or more days after receiving a single vaccine dose.

● Vaccinated then Recovered: Individuals who had been vaccinated with one or two doses and were later infected.

● Vaccinated: Individuals seven days or more after receiving the second dose, and who had not been infected before the start of the study period.

● Booster: Individuals who received a third (booster) dose 12 or more days previously and had not been infected before the start of the study period.

And later...

The first infections of individuals in the Recovered and hybrid cohorts were from mostly the pre-Alpha and the Alpha variants. If protection provided by prior infection depends on the variant, its effect is confounded with the effect of time since infection. As a single variant was dominant in Israel during each of the pandemic waves,17 our study cannot disentangle the two effects. Moreover, infections during the study period were mostly of the Delta variant, and there is not enough information at this time to suggest implications from our results regarding protection from new variants such as the Omikron.

Another source of potential bias is due to cohort misclassification. To be classified as a recovered person in our study, a PCR test must have been performed and found positive. However, many infected individuals have not been diagnosed and some of these have received vaccination. Thus, some of those classified into the Vaccinated cohort or the Booster cohort should have been included in the hybrid-immunity cohorts. This may have led to underestimation of the rate among vaccinated uninfected individuals. Yet, as the Recovered group was much smaller than the Vaccinated group (see Table 1), the size of this bias is expected not to be large.

Expand full comment
Brian Mowrey's avatar

Right, so both the single and double-dosed are included in vaxed + recovered. That was my impression given the days to infection chart. Thanks for highlighting the relevant text.

Expand full comment
Andreas Oehler's avatar

did you look at the additional materials to the study?

Expand full comment