The US Centers for Disease Control and Prevention maintains that vaccines against Covid-19 provide a high degree of protection against severe infections, hospitalisations and death, though the US is seeing “concerning evidence of waning vaccine effectiveness over time and against the Delta variant,” according to director Rochelle Walensky.
“We are concerned that the current strong protection against severe infection, hospitalisation and death could decrease in the months ahead, especially among those who are at high risk or who were vaccinated earlier,” the CDC director said during a virtual briefing on 18 August.
The update from White House officials follows recommendations from federal health officials to offer a third “booster” shot eight months after a second dose of the two-dose Pfizer and Moderna vaccines, effective on 20 September.
“The overall purpose of vaccines is to keep us out of the hospital,” said US Surgeon General Vivek Murthy.
But if a current trajectory of rising infections continues amid the widespread transmission of the more-contagious Delta variant, “we will likely see an increase in breakthrough hospitalisations and breakthrough deaths,” he said. “That’s how we came to the eight month mark.”
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The spread of the more-contagious and dominant Delta variant – in which a virus replicates and mutates through transmission – and climbing rates of severe illness among unvaccinated people have overstressed health systems across the US, as public health officials have amplified vaccination efforts as the best defence to keep people out of hospitals.
New research from the US, Israel and the UK has shown a partial decline in vaccine efficacy against mild to moderate to severe infections, though it is unclear whether that decline has followed dropping levels of immunity, a rise in transmissions amid dropped restrictions and less-stringent health guidelines like wearing masks, or the Delta variant’s dominance, or a combination of all three factors.
People inoculated against Covid-19 lose higher levels of vaccine efficacy as antibodies decline over time, and higher levels of antibody protections from a “booster” dose may be required to provide stronger protection against Delta, according to chief medical adviser Anthony Fauci.
Those booster doses will remain free for all Americans regardless of insurance or immigration status, officials said.
Health officials will evaluate whether people under age 18 will be eligible for a third dose, and whether Americans who received the single-shot Johnson & Johnson vaccine will require another dose.
A third-dose distribution must first be authorised by the US Food and Drug Administration, and a CDC advisory committee will review evidence and make recommendations.