Booster shots of COVID-19 vaccines wane in strength and become less likely to protect recipients from the coronavirus, a new study by the Centers for Disease Control and Prevention (CDC) has found.

As per CDC data, the effectiveness of booster shots of the COVID-19 vaccine against hospitalisations during the omicron surge in the US was found to decrease from 91% in the first two months after the booster jab, to 78% around the fourth month.

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Data from the CDC also showed that protection offered by booster shots declined more sharply with regard to preventing visits to urgent care centres or emergency departments: while booster shots were 87% effective in preventing emergency care visits in the first two months after the jab, the figure dropped sharply to 66% around the fourth month. After about five months, booster shots were found to be only 37% effective in terms of preventing emergency care visits.

The study went on to say that its finding “reinforces the importance of further consideration of additional doses to sustain or improve protection against COVID-19-associated” emergency care visits and hospitalisations.

The CDC study comes days after Dr Anthony Fauci, Chief Medical Advisor to President Joe Biden, said at a White House press briefing that officials would base decisions on booster shot allocations based on real-world data on “efficacy in preventing, for example, hospital visits, as well as hospitalizations.”

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“There may be the need for yet again another boost — in this case, a fourth-dose boost for an individual receiving the mRNA [vaccine] — that could be based on age, as well as underlying conditions,” Dr Fauci had said on Wednesday.

Many in the US received their booster shot months ago, and the study’s findings highlight that they might not be as well-protected against the coronavirus as initially thought. It remains to be seen how the government responds to the CDC’s new findings.