NEW YORK (NYTIMES) – A day after President Joe Biden issued broad vaccine mandates aimed at propelling US workers to get vaccinated against the coronavirus, federal health officials released a handful of studies highlighting how effective the shots are at preventing infections, hospitalisations and deaths – even while the highly contagious Delta variant has been dominant.
Three studies that drew data from different US regions evaluated the protective power of the vaccines. One looked at more than 600,000 Covid-19 cases in 13 states, representing about one-quarter of the United States population, between April and July, and concluded that individuals who were not fully vaccinated were far more susceptible to infection and death from the virus.
They were 4½ times more likely than vaccinated individuals to become infected, 10 times more likely to be hospitalised and 11 times more likely to die from the coronavirus, the study found.
Vaccine protection against hospitalisation and death remained strong even when the Delta variant was the dominant form of infection. But the vaccines’ effectiveness in preventing infection dropped to 78 per cent from 91 per cent, the study found.
The studies underscore a series of similar findings in recent weeks.
“As we have shown, study after study, vaccination works,” said Dr Rochelle Walensky, director of the Centres for Disease Control and Prevention, at a White House Covid-19 briefing on Friday (Sept 10).
As more and more Americans become vaccinated, experts always expected that immunised people would represent a greater percentage of hospitalised patients.
“What I want to reiterate here is that it’s still well over 90 per cent of people who are in the hospital who are unvaccinated,” Dr Walensky said.
“We still have more than 10 times the number of people in the hospital who are unvaccinated, compared to vaccinated,” she added.
Two other studies published on Friday detected waning protection from the vaccines among older adults.
One study, conducted at five Veterans Affairs Medical Centres, found that protection against hospitalisation declined with age, to 80 per cent for those age 66 and older, down from 95 per cent for adults aged 18 to 64. A second study found vaccine effectiveness dropped off at age 75.
The findings could help identify populations that may be in need of additional doses or booster shots. In August, the Food and Drug Administration authorised giving third doses of Pfizer-BioNTech’s and Moderna’s Covid-19 vaccines to some people with weakened immune systems, including organ transplant patients.
But officials have said there is insufficient data on whether the vaccines’ effectiveness declines over time to recommend boosters for healthy adults.
The data also suggests that the Moderna vaccine may be slightly more effective at preventing infections and hospitalisations with the Delta variant, compared with the Pfizer-BioNTech vaccine. Both of the mRNA vaccines had higher efficacy rates than the Johnson & Johnson shot, but the studies were not originally designed to evaluate the comparative effectiveness of different vaccinations.
In the study of 33,000 medical encounters in nine states between June and August, the Moderna vaccine had an effectiveness rate of 92 per cent against infection, compared with 77 per cent for the Pfizer-BioNTech shot.
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