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Most of the protective power offered by booster doses of coronavirus vaccines falls after four months, the US Centers for Disease Control and Prevention (CDC) said, raising concerns that some Americans, especially those at high risk, will have to take a fourth dose.
Preliminary research from Israel and Britain has suggested that the protection offered by booster doses falls within months.
But the data released on February 11 show the first evidence of declining protection against vaccines produced with mRNA technology, such as those of Pfizer and Moderna.
The study focused on people who sought medical treatment because of the symptoms of COVID-19 disease, so if that population is geared toward older ages and those with weaker immune systems, then booster doses may be lower. effective.
Other studies have shown that while vaccines may lose some of the ability to protect against serious illness, hospitalization in people over 65, they are very effective against young people who do not have concomitant diseases.
But U.S. health officials have said they need to understand whether people at high risk will need to undergo the three-dose regimen or take the fourth dose.
The CDC had previously published data showing that the second and third doses of Moderna and Pifzer vaccines may be less effective against the Omicron variant than the Delta variant of the coronavirus. According to these data, the CDC had said that the third dose could provide protection, at least for a short time.
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