Three studies by the Centers for Disease Control and Prevention published Friday show that COVID-19 vaccines are generally resistant to the hyper-transmissible variant of the delta coronavirus.
According to studies, people who are fully vaccinated are five times less likely than others to contract delta. They also have a 10x lower chance of being hospitalized with COVID-19 from Delta.
This new data comes just days after President Biden issued broad vaccine mandates-the most aggressive move yet by the administration to force vaccine holdouts to get the lifesaving shot. Around 80 million Americans are eligible for vaccination, but have not received the free and readily available shots. Since June, the spread of delta virus has been rapid and widespread across the country, resulting in one of the most severe COVID-19 pandemics. The US currently has nearly 150,000 new cases per day. There are also over 1,500 daily deaths. Nearly all of these can be prevented with vaccination.
Although there is concern about vaccine effectiveness dropping due to the popularity of the delta variant, data shows that the shots are still working well. The effectiveness of existing vaccines against infection has declined slightly with the dominance of the delta variant, but vaccination still provides powerful protection from both hospitalizations and death from the disease.
Public health researchers examined data from more than 600,000 COVID-19 adults in 13 US jurisdictions. They did this over two time periods. A pre-delta period ran from April 4 through June 19, and a post delta period ran from June 20 through July 17. Researchers then calculated the age-standardized ratios between hospitalizations and deaths for fully and partially vaccinated individuals in each period.
The pre-delta period saw a decrease in infection rates for fully vaccinated individuals compared to those who were not (with a 95% confidence interval of 7.8-15.8). This ratio fell to 4.6 in the post-delta period, with a 95 percent confidence interval between 2.5 and 8.5.
Before delta, people who had been fully vaccinated were 13 times more likely to be admitted to hospital than those who hadn't (confidence interval 11.3 to 15.6). This ratio fell slightly to 10% after delta (confidence interval of 8.1 to 13.3). Fully vaccinated people were 16.6 times more likely to die from COVID-19 before delta (confidence interval 13.5 to 20,4) and 11.3x less likely after delta (confidence interval 9.1 to 13.9).
According to the study authors, these findings "confirm with a possible decline in vaccine protection against confirmed SARS/CoV-2 infection, and continued strong protection from COVID-19associated hospitalizations and deaths."
After further analyzing the data and accounting for vaccine coverage over the two periods, the authors made rough estimates of how the effectiveness of vaccines changed between the intervals. They estimated that vaccine effectiveness fell from 91 to 78 percent with the use of delta for protection against infection. Protection against hospitalizations was shown to be between 92 percent and 90 percent. For death prevention, it was between 94 percent and 91 percent.
Hints at trouble
It was troubling to note that protection declined more in older age groups. Those 65 years and older saw larger drops.
The CDC released a second study on Friday that examined nearly 33,000 COVID-19 adult cases from hospitals, emergency rooms, and clinics. The overall post-delta vaccine effectiveness against hospitalization was about 86 per cent according to that analysis. The researchers found that vaccine effectiveness against hospitalizations was only 76 percent for people 75 years and older when they split the data by age.
Researchers again found an age-based drop in vaccine effectiveness against hospitalization in a smaller, third study that involved just over 1000 people from five Veterans Affairs Medical Centers. The overall effectiveness of vaccines in preventing hospitalization was about 87 percent, according to the delta. For people aged 18-64, the rate of hospitalization protection was exceptional at 95 percent. However, it was only 80 percent for those 65 years and older.
It's not clear at this time if the drops observed in the studies are due either to the power and/or a decrease in protection after initial vaccination, or both. The data that was released today will be crucial in future decisions regarding the availability and timing of booster shots in the US.
Biden's administration announced it will offer booster doses to all Americans 12 years and older starting on September 20th. The Food and Drug Administration is yet to approve boosters. Internal frustrations have already been expressed by regulators over the administration's initial plans. Further questions surround the looming booster decisions. The CDC advisory committee, which sets official guidance for vaccine use, has no meeting scheduled after September 29.