Credit ACIP/CDC
#16,671
In early December, just weeks after the Omicron variant was announced by researchers from South Africa, Pfizer-Biontech released preliminary data (see The Omicron Uncertainty Principle) indicating that while two shots of their mRNA vaccine wasn't very protective against Omicron, a 3rd (booster) shot increased its effectiveness 25-fold.
How long that enhanced protection might last was unknown.
Early reports suggested those boosted by a 3rd shot were still apt to see `breakthrough' infections with Omicron, but they remained well protected against severe disease, hospitalization, and death.
In late December, Denmark's SSI released a report (see SSI Preprint: Effectiveness of 2-dose or Booster mRNA Vaccination Against Delta/Omicron), citing a 54% VE (Vaccine Effectiveness) of the booster against Omicron infection, but they didn't have enough data to determine how protective it might be against severe illness.
Yesterday these same researchers published a preprint, which updates this information, and finds the mRNA booster provided substantial protection (88.8% - 90.2%) against severe Omicron infection. While that protection fades somewhat over time, it remains respectably high (66.2% to 77.3%) after 120 days.
First, the summary from Denmark's SSI (Statens Serum Institut), followed by a link to the preprint and some excerpts from the Abstract. I'll have a brief postscript after the break.
(translated)
The 3rd connector increases protection against the omicron variant
A study from Statens Serum Institut shows that you get increased protection against infection with the omicron variant after three doses with the Pfizer-BioNTech vaccine or the Moderna vaccine.
Last edited on April 5, 2022
Initial calculations of vaccine efficacy across the omicron variant have now been updated. New figures from Statens Serum Institut (SSI) show that three vaccine doses with either Pfizer-BioNTech or Moderna protect almost 50% against infection and even more against serious disease.
The protection obtained against infection with the omicron variant after two doses of mRNA COVID-19 vaccine decreases over time. But vaccine effectiveness increases again after a third dose. In particular, the protection against hospitalization. If infected with the omicron variant, high.
This is the conclusion of the study, which is a collaboration across the SSI.
Read the full study, which is not yet peer-reviewed, but can be seen in preprint at Research Square.
Protection against serious illness
As I said, the vaccines protect against being admitted to the hospital if you nevertheless become infected.
Thus, in the study, a protection of between 88.8% and 90.2% is seen immediately after the third dose of mRNA.
And the protection continues. In people vaccinated with the third dose more than 121 days ago, a relatively good effectiveness of 66.2% to 77.3% continues to be observed. This, in turn, is compared to unvaccinated.
Three vaccine doses work
The study covers a period starting on 28 December 2021. Here, the omicron variant accounted for approximately 90% of the cases, and there was widespread societal infection and thus a large data base.
Compared to unvaccinated individuals, the vaccine efficacy against infection with the omicron variant of the covid-19 vaccine from Pfizer-BioNTech is estimated at 37% immediately after the second dose. After more than 121 days after vaccination, this effect has decreased to 9.8%.
However, vaccine efficacy increases again to 47.9% immediately after the third dose. This means that people who have recently received the 3rd bite are infected with omicron in up to half as few cases as unvaccinated people do.
For the covid-19 vaccine from Moderna, the vaccine efficacy against infection with the omicron variant is estimated at 37.9% immediately after the second dose. The effect drops to 13.2% when more than 121 days have passed since vaccination. Vaccine efficacy increases again to 47.7% immediately after the third dose.
Read more
Read the full study, which is not yet peer-reviewed but can be viewed in preprint at Research Square.
Vaccine effectiveness against infection and COVID-19-associated hospitalisation with the Omicron (B.1.1.529) variant after vaccination with the BNT162b2 or mRNA-1273 vaccine: A nationwide Danish cohort study
Christian Hansen, Astrid Schelde, Ida Moustsen-Helm, Hanne-Dorthe Embor, Rasmus Eriksen, Marc Stegger, Tyra Krause, Kåre Mølbak, Palle Valentiner-Branth
DOI: 10.21203/rs.3.rs-1486018/v1
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Abstract
Limited evidence exists on the level and longevity of protection afforded by current COVID-19 vaccines against infection and hospitalisation with the Omicron variant. SARS-CoV-2 PCR testing rates in Denmark are exceptionally high.
In this nationwide cohort analysis, from December 28, 2021 to February 15, 2022 during which Omicron was the predominant variant, PCR testing data are combined with other national register data with near-complete information on all vaccinations, hospitalisations and comorbidities in the population. Trends over time in vaccine effectiveness after two and three doses with BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna) are estimated using Cox regression.
Despite relatively poor protection against infection (symptomatic or asymptomatic), vaccine effectiveness against COVID-19-associated hospitalisation was high after the third dose declining from 88.8% (95% CI: 87.3 to 90.1%) to 79.0% (76.5 to 81.3%) for BNT162b2 and 90.2% (87.3 to 92.5%) to 83.6% (77.7 to 88.0%) for mRNA-1273 over the first four months after vaccination.
These results are even more reassuring when you look at the low hospitalization rate in Denmark despite record infections (see Denmark SSI: Omicron Risk Assessment - Record High Infection Rates, But Hospitalizations Remain Low), with the added bonus that Denmark's epidemic was driven in large part by the BA.2 variant.
Most people who received the booster last fall are now well beyond the 120-day limit of this study, and we really don't know how much of a drop off in protection that first booster suffers after 6 or 8 months.
For that reason, last week the United States approved a 2nd booster for those over 50 and more than 4 months since their last booster (see FDA & CDC Approve 2nd Booster For Older Americans).
While we continue to hear that Omicron is `milder' than previous COVID variants, in most cases those reports have come from highly-vaccinated countries, like Denmark.
In places where vaccine uptake has been less rigorous - like Hong Kong - Omicron's impact has been significantly greater. Which is why I expect to get my second booster in the weeks ahead.
