A mutation of COVID-19 is spreading quickly throughout the world and threatens recovery efforts. The Alpha variant is believed to be 50% more transmissible than other local COVID-19 types. The Delta variant is 60% more transmissible than the Alpha variant.
Vaccine effectiveness is a concern with variants. Two doses of the Pfizer vaccine were 88% effective against the Delta variant (compared to 93% for Alpha). However, a single dose of Pfizer of AstraZeneca is 33% effective against Delta (compared to 50% for Alpha).
As a result, the WHO recommends that even vaccinated people wear masks.
Read Delta coronavirus variant: scientists brace for impact in Nature.
See also:
- What will the highly transmissible Delta variant’s effect on the R value?
- Clinical trials of the COVID-19 vaccine was not designed to discover the optimal regimen for public health and they will need to reassess for variants
Links to this note
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Breakthrough COVID-19 Cases Are 74% Adults 65 or Older
CDC data shows that 74 percent of breakthrough COVID-19 cases are among adults 65 or older and make up the vast majority of vaccinated people that are hospitalized.
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90% of the Population Needs to Be Vaccinated for Herd Immunity from the Delta Variant
Because the COVID-19 Delta variant is much more transmissible (translating to a higher R rate of 50-100% higher than a year ago) and mRNA vaccines are 90% effective, we need 90% of the population to be vaccinated to achieve herd immunity. Unfortunately that seems unlikely due to the politicization of the vaccine.
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COVID-19 Omicron Variant of Concern
The World Health Organization (WHO) classified B.1.1.529 (omicron), first detected in South Africa, as a COVID-19 variant of concern.
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COVID-19 Vaccine Is 33 Percent Effective Against Omicron
A study of 211,000 COVID-19 cases and 78,000 Omicron variant cases found that the vaccine is only 33% effective at preventing infection by 70% effective at preventing hospitalization.
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Base Rate Fallacy Shows How Headlines About COVID-19 Infections of Vaccinated People Is Overblown
We’re starting to see news outlets say there is an alarming trend where vaccinated people are getting COVID-19 (such as this one from the WSJ). This is an example of base rate fallacy—in a population with a high vaccination rate it is inevitable that new cases include vaccinated people (especially in a country like Israel with extremely high vaccination rate). We should not take that to mean vaccines are suddenly ineffective (they’re not).
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Half of COVID-19 Survivors Had Lingering Symptoms After 1 Year
A study in China of COVID-19 survivors (median age 59) who were hospitalized found that half had a persisting symptom one year later—Long COVID. That includes shortness of breath, fatigue, and mental health issues such as anxiety depression. It also found a higher prevalence of problems with mobility and pain and discomfort than the control group.