A recent preprint study examining Coronavirus Disease 2019 (COVID-19) patient data collected by the Canadian province of Ontario found that takers of a two-dose course of either the Moderna or Pfizer messenger RNA gene therapy injections generated negative vaccine efficacy against Omicron as little as 60 days after receiving the second dose.
The Jan. 1 study, conducted by almost entirely Toronto-area scientists and funded by grants from the Ontario Ministry of Health and the Public Health Agency of Canada, examined “provincial SARS-CoV-2 laboratory testing, reportable disease, COVID-19 vaccination, and health administrative databases,” among those aged 18+ who underwent a PCR test between Nov. 22 and Dec. 19, 2021.
The methodology used in the study notably excluded residents of long-term care homes, those who had only received one dose of injection or the second dose within 7 days of their test, and those who had accepted the AstraZeneca adenovirus vector double-stranded DNA injection from its cohort.
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All positive tests were considered “confirmed COVID-19 cases irrespective of symptoms or severity,” while negative tests among those who also tested positive within the previous 90 days were excluded from the control group.
In the 27-day-period the analysis examined, 471,545 negative tests were registered, alongside 9,201 Delta variant and 3,442 Omicron variant positives.
Notably, Omicron positives were younger, had less comorbidities, and were almost entirely double vaccinated individuals compared to the Delta-positive control.
The bulk of Omicron positives were in those aged 18 to 29 at 44.4 percent, followed by 21.6 percent 30 to 39, and 18.5 percent 40 to 49. Cumulatively, 84.5 percent of all positive Omicron cases were aged between 18 and 49.
By contrast, the Delta control registered only 66.6 percent positives in the 18 to 49 category, and only 21.8 percent of all positives were in the 18 to 29 age bracket.
The Delta control also contained patients tagged as possessing “any comorbidity” at 43.3 percent, compared to only 35.3 percent for Omicron.
Researchers also found that not only did 90.1 percent of Omicron positives occur in double-vaccinated individuals, only 5.1 percent, or 176 cases in total, occurred in unvaccinated individuals.
In comparison to the Delta control, 64.6 percent of all cases occurred in double vaccinated individuals and 33.1 percent in the unvaccinated.
Booster recipients amounted to 2.3 percent of all Delta positives and 4.8 percent of all Omicron positives.
The study notes, however, that Ontario did not make booster injections available to those under 70 until Dec. 13 when it decreased the age to 50. The Province made boosters available to everyone 18+ on Dec. 18.
A majority of double vaccinated individuals tested positive for Omicron between 120 and 179 days after receiving their second dose at 65.6 percent. This measure of waning efficacy is contrasted by only 47.2 percent in the Delta and 60.0 percent in the negative-test controls during the same period.
In using this data to assess vaccine effectiveness (VE), the paper gives the following methodology employed via SAS:
“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. VE was calculated using the formula VE=(1-OR)x100%. For both Omicron and Delta infections, we estimated VE by vaccine schedule and time since latest dose.”
Covariates employed included not only 2019-2021 influenza season vaccination status, but somewhat extraneous factors such as, “Neighbourhood-level information on median household income, proportion of the working population employed as non-health essential workers, mean number of persons per dwelling, and proportion of the population who self-identify as a visible minority.”
While the calculation showed that VE for two doses of injection against Delta was as high as 84 between 7 and 59 days post injection, waning to 71 after 240 days, the measurement against Omicron was anything but confidence inspiring.
The study found VE against Omicron between 7 and 59 days post double-injection was only 6, falling into the negatives at -13 between 60 and 119 days, -38 between 120 and 179 days, and -42 between 180 and 239 days.
Although researchers calculated the VE generated by booster recipients against Omicron as being as high as 34 for Pfizer and 59 for Moderna 7 days after injection, data nonetheless showed that 4.8 percent of all Omicron positives and 2.3 percent of all Delta positives were boosted.
The above is significant since the majority of all infections occurred in age brackets that did not have access to boosters until Dec. 18 in a study that finished collecting data only a day later on Dec. 19.
Roughly 64.5 percent of boosted Omicron positives recorded in the study had received their booster 7 to 59 days prior.
In the Discussion portion of the paper, researchers noted that in circumstances wherein vaccines are not effective against Omicron, vaccine passports may actually be contributing to the spread, “The behaviour of individuals who are vaccinated, and the policies that apply to this group, may differ from those who are unvaccinated such that ‘vaccinated’ status could be associated with an increased risk of exposure,” authors stated.
“Younger adults may be more likely to frequent such venues and have more social contacts (and Omicron cases in our study were younger). As such, the exposure risk of vaccinated individuals may be higher than unvaccinated individuals since vaccination is a requirement to participate in these social activities.”
“This may explain the negative VE following 2 doses observed for Omicron during this early study period.”