CDC study: Confirmed the effect of vaccine booster to prevent aggravation, yet the effect dropped in a few months

Recently CNN.co.jp reported the following:

追加接種の重症化予防効果を確認、数カ月で低下も　ＣＤＣ研究

2022.02.14 Mon posted at 17:05 JST

（ＣＮＮ） 米ファイザー、モデルナ製の新型コロナウイルスワクチンを追加接種した場合、重症化を防ぐ効果は高い一方、数カ月で低下するとの傾向が、米疾病対策センター（ＣＤＣ）の研究で明らかになった。

研究チームは、米国内の計１０州で昨年８月２６日から今年１月２２日までの間にワクチンを２回または３回接種した成人のうち、コロナ関連の救急診療を受けた２４万１２０４人、入院した９万３４０８人のデータを分析。その結果を１１日付のＣＤＣ疫学週報で報告した。

データによると、米国内でオミクロン株が流行していた時期については、３回目の接種を受けてから２カ月後までにコロナ関連の救急診療を防ぐ効果は８７％、入院を防ぐ効果は９１％に上ったが、この数値は接種の４カ月後にそれぞれ６６％、７８％に低下した。

２回接種の場合は、接種後２カ月以内の入院防止効果が７１％、５カ月目以降は５４％に下がっていた。

デルタ株が流行していた時期の入院防止効果は、３回接種から２カ月以内が９６％で、数カ月後に７６％まで低下した。ただし、この時期に３回目接種から４カ月以上たっていたケースはほとんどないため、低下の幅は正確でない可能性がある。

研究者らはこの結果を受け、３回目の接種は効果的だが、予防効果を維持するためにはさらなる追加接種を検討するべきとの見方を示した。

ＣＤＣが発表した別の研究では、昨年９月から今年２月に追加接種を受けた成人７２万１５６２人について連邦当局に報告された有害事象を分析した結果、３回目も同じ種類のワクチンを打った場合、副反応は２回目の後より出にくい傾向が判明したと報告された。

Translation 

(CNN) A study by the Centers for Disease Control and Prevention (CDC) found that a new coronavirus vaccine booster made by Pfizer and Moderna would be highly effective in preventing aggravation, but effectiveness tended to decrease in a few months.

The research team found that among adults who had been vaccinated twice or three times between August 26 last year and January 22 this year in 10 states in total in the United States, the analyzed data showed that 241,204 received corona-related emergency medical care and 93,408 people were hospitalized. The results were reported in the CDC Epidemiology Weekly Report dated 11th.

According to the data, when the Omicron strain was prevalent in the United States, within two months after receiving the third vaccination, vaccination was 87% effective in preventing corona-related emergency medical care, and was 91% effective in preventing hospitalization. However, 4 months after inoculation, this number dropped to 66% and 78% respectively.

In the case of the second vaccination, the hospitalization prevention effect within 2 months after vaccination was 71%, and reduced to 54% after 5 months.

In preventing hospitalization during the period when the Delta strain was prevalent, the effect was 96% within 2 months after the 3rd inoculation, it decreased to 76% after several months. However, because in this period the cases of those over four months after the third inoculation was few, the extent of the decline might not be known accurately.

In response to this result, the researchers said that while the third vaccination was effective, additional boosters to maintain the preventive effect had to be reconsidered.

In another study published by the CDC to analyze adverse events reported to federal authorities, in 721,562 adults who received boosters from September last year to February this year by giving them the same type of vaccine for the third time, it was reported that side reactions tended to be less likely to occur compared to after the second-round vaccination.

              So, vaccine booster made by Pfizer and Moderna is highly effective in preventing aggravation, but its effectiveness tends to decrease in a few months. I am wondering if vaccination would become a regular activity in the many years to come.