Ontario data January 1
3,442 Omicron-+cases, 9,201 Delta-+ cases, and 471,545 test-negative.controls
Our results demonstrate that the effectiveness of 2 doses of COVID-19 vaccines against infection
(irrespective of symptoms or severity) is substantially lower for Omicron than Delta,
and that VE against Omicron infection was only 37% ≥7 days following a third dose.
We also observed negative VE against Omicron among those who had received 2 doses compared to unvaccinated individuals.
Negative VE versus unvaccinated??? hmmm? for the doubly vaccinated?
37%? Formerly, govs would not accept a vaccine if it had 50% VE,,,, what has changed?
Right RB - so we are all agreed:
- Boosters protect against infection (for 3 months, maybe not much longer)
- Vaccination protects against severe disease. Boosters increase this protection, this severe disease protection does not wane in the same way that infection protection does.
There are the well known (to you - I'm sure) biological reasons for this difference.
Now as far as two doses of vaccine giving negative VE (against omicron infection long after vaccination) I refer you to the paper you linked:
Our analysis has several limitations. First, we were unable to differentiate individuals who received a third dose as part of an extended primary series (i.e., severely or moderately immunocompromised individuals) as well as those who were eligible for a third dose earlier (e.g., residents of retirement homes). As such, the proportion of our sample with a third dose may reflect these highly vulnerable populations, and thus VE may be lower than for the general population due to underlying comorbidities, for example. Second, due to sample size constraints, we were unable to provide age-specific VE estimates. Third, we were unable to estimate effectiveness against severe outcomes, due to the lag between infection and hospitalization or death. Fourth, there may be residual confounding that was not accounted for in our analysis. This includes an inability to control for previous undocumented infections, which may be differential by vaccination status, as well as confounding due to behavioural patterns. For example, if vaccinated individuals have more exposure to SARS-CoV-2, our VE estimates are likely underestimated.21 Last, changes in testing patterns, including increased use of rapid antigen tests (which are not captured in our data) and decreased PCR testing availability, may have impacted our estimates, but the direction of any resulting bias is uncertain.
And in addition, from the paper:
We used multivariable logistic regression to estimate odds ratios comparing the odds of vaccination in each “time since latest dose” interval among cases with the odds among controls, while adjusting for all listed covariates and a categorical variable for week of test.
As a confounder, varying COVID rate across age groups, and with time, affects results. For omicron, with its super-fast attack rate, a resolution of one week is too low, rates in the UK were doubling every 2 days some times, in some age groups.
So while I'm interested in these results, and would not rule out some negative effect of old vaccination on omicron VE, the data here does not support any such conclusion, much more work needs to be done.
You know that right? Cos you are not an anti-vaxxer and therefore do not jump to conclusions?