Robust Covid-19 Booster Protection Wanes After Four Months, CDC Says

The CDC report said the findings underscored the importance of receiving a third mRNA vaccine dose to prevent hospitalization as well as emergency-care visits.

Without a third booster shot, protection against hospitalization within two months of a second shot was 71%, and fell to 54% after five months.

Vaccine effectiveness also waned against Covid-19 cases leading to an urgent-care or emergency-room visit. During the Omicron period, the protection rate fell from 87% within two months of a third dose to 66% after four to five months, and to 31% five months more after a third shot.

Messenger RNA shots from

Pfizer Inc.

and partner

BioNTech SE

and from

Moderna Inc.

are the most widely used Covid-19 vaccines in the US After the Omicron variant began spreading, early research indicated the initial two shots weren’t as effective as they had been against earlier strains, but the booster shot provided strong protection.

The CDC study looked at hospitalization data from 10 states from Aug. 26 through Jan. 22, through most of which the Delta variant was the dominant strain. Omicron became the dominant variant around Dec. 20.

During the Delta-predominant period, protection against hospitalization was 96% within two months of a third shot, and fell to 76% within four months or more after the third shot.

Over the entire five-month period analyzed by the CDC, 43% of people hospitalized with Covid-19-like illness were unvaccinated, 45% received two vaccine shots and 12% had gotten three shots, the CDC said.

Coronavirus-related hospitalizations have continued to decline in the US, with the seven-day average of patients with confirmed or suspected Covid-19 dropping 35% from a Jan. 20 peak at 103,464, according to data from the Department of Health and Human Services.

The rolling seven-day average of daily deaths with Covid-19, a lagging indicator, shows attempted signs of stabilizing, reaching 2,466 on Wednesday, compared with 2,531 on Monday, according to data from Johns Hopkins University. Covid-19 deaths in the US have been averaging above 2,400 a day since Jan. 28 and running at their highest level since February last year.

New confirmed infections with the virus in the US and the European Union have been falling from their peaks in January.

In the EU, average Covid-19 deaths have risen to more than 2,000 a day again as the Omicron wave continues to take a deadly toll in Italy, France, Spain and some other countries. However, declining overall infections have made epidemiologists optimistic that deaths too will peak soon.

Confirmed Covid-19 cases in France have fallen at an accelerating rate, with an average of 201,694 new cases a day over the week ended Feb. 7, down 34% from a week earlier. As of Thursday evening, France’s weekly average of daily hospital admissions was down 9% from a week earlier, while intensive-care unit admissions were down 6%. Deaths have continued to rise, reaching a daily average of 286 on Thursday. In another sign of receding overall contagion, some 2% of school classes were closed on Friday due to Covid-19 infections, a steep fall from the 3.2% that were closed the previous week, according to data from France’s Education Ministry.

Italy on Thursday passed 150,000 confirmed Covid-19 deaths since the start of the pandemic. The first country outside Asia that was hit on a large scale by Covid-19, Italy has Europe’s second-highest overall death toll from the virus, after the UK

Italy’s average daily deaths in the winter wave have stabilized at more than 360, but health experts say mortality will likely recede soon as overall Omicron cases decline. Confirmed infections have dropped fast in Italy too, with the seven-day average of new confirmed cases falling below 90,000 this week, compared with more than 180,000 in mid-January.

The picture is more mixed in Germany, where the seven-day incidence of infections has continued to rise. But Germany on Thursday registered a daily drop in infections compared with the same day last week for the first time in 2022. The country’s disease-control center, the Robert Koch Institute, said new confirmed cases fell to 240,172 on Thursday, from 247,862 a week earlier.

German health experts say strict social-distancing measures, which are particularly severe for the unvaccinated, meant that Omicron infections had risen more slowly in Germany than in many neighboring countries and would therefore take longer to peak. Despite pressure from businesses and civil society, German authorities have said it would be weeks before the measures are relaxed.

Write to Joseph Walker at [email protected]Nick Kostov at [email protected] and Bertrand Benoit at [email protected]