Israel considers fourth booster dose against covid-19 2:32
(CNN) --
The US Food and Drug Administration (FDA) has expanded the emergency use authorization for Pfizer and Moderna's COVID-19 vaccines to allow adults over 50 years receive a second booster dose as soon as four months after their first booster dose of any COVID-19 vaccine.
The measure expands the availability of additional boosters for healthy older adults.
The FDA had previously allowed second booster doses for anyone age 12 and older who had a severe immune deficiency, beginning four months after their first booster.
The US Centers for Disease Control and Prevention (CDC) is expected to follow up with what is known as a permissive recommendation, a statement that vaccines can be used in this group of age for those who want them.
However, the agency is not expected to officially recommend the vaccines.
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Is a second booster dose necessary?
There is general scientific agreement that third doses help boost immunity against serious illness from the virus that causes covid-19.
But science is far from deciding whether or even when the fourth dose might be necessary, as vaccines continue to offer a high degree of protection against hospitalization and death from Covid-19, even as protection against the disease declines.
Much of the evidence examining the safety and efficacy of a second booster dose of the vaccine comes from Israel, which has been recommending a fourth dose of the coronavirus vaccine for adults 18 and older since late January.
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In a large study of more than half a million adults over the age of 60, those who received a second booster, or fourth dose, of a Covid-19 vaccine were 78% less likely to die during the omicron wave. compared to those who received a third dose at least four months earlier.
But the number of deaths was relatively low in both groups.
After 40 days of follow-up, there were 232 total deaths among nearly 234,000 people who had only received three doses of the Pfizer-BioNTech vaccine, compared with 92 deaths among 328,000 people.
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A smaller study of healthcare workers, including younger adults, found that fourth boosters were safe and restored antibodies to the same levels achieved after the third dose.
But the fourth doses were only moderately effective (about 30% to 40%) in preventing the disease.
And most of the workers who got sick still had high viral loads, suggesting they were capable of transmitting the infection to others.
Additional studies from the UK show that the antibody boost from a booster dose wears off very quickly, within weeks.
So some experts believe that, given the resources available and the decreased appetite for continuing to receive more and more boosters, the United States should wait until there is a clear danger of a new wave of infections to implement the fourth dose.
covid-19vaccine against covid-19