Hi #epitwitter, sorry to pile on with bad news, but we’re not as immune as we think, and it’s not just #Omicron‘s immune escape. In southern New England, it turns out that ~27% of vaccines were given to previously infected individuals. Pre-print below. 1/ medrxiv.org/content/10.110…
Estimates are that 34% of vaccines in Rhode Island, 28% in Massachusetts, and 25% in Connecticut were administered to seropositives. This is consistent Moghadas et al’s ballpark estimate that half of previously infected individuals were vaccinated. 2/ acpjournals.org/doi/full/10.73…
This means we overestimated the effect of the winter/spring 2021 vaccination campaign. N Engl was >33% immunologically naive when #DeltaVariant caused an upturn in cases in late July. Our inability to infer this in real time was the reason none of us predicted the #Delta surge 3/
Table below shows the breakdown as of 5/31/2021 of past infection & vaccination history in RI/MA/CT. Third column shows the group that we now know #Omicron will be able to infect. Add the fourth column to 30% or 50% of the third column, and this is Omicron’s susceptible pool. 4/ 
( Of course, above, you will have to add in all the Delta infections from July to Oct, factor in some waned immunity, and account for boosters ). 5/
Graph below shows the attack rates (blue) and population immunity (green) through May 31. We were a bit underwhelmed by the 64% to 73% population immunity seen in these three states. This is not enough to protect against a new wave of infection with #Delta or #Omicron 6/ 
Finally, as we perform inference on 11 clinical data streams to arrive at these estimates, this is a reminder that SARS-CoV-2 infections fatality rates were much higher in March-April 2020 than in any other period. IFR was >1.3% in all three states during this time. 7/
Thx @athutran @nathanwikle for putting this together so quickly & @Fuhan_Yang @fcraw4d for helping put all the @CTDPH data together. Thx @RIHEALTH @MassDPH @ciddpsu @BillHanage & @SACEMAdirector @Tuliodna @DarrenM98230782 for making all the Omicron results available so early. 8/