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.
- 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
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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.
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.
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).
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.