WASHINGTON – A new study by Pfizer and BioNTech suggests that its updated Covid-19 booster is better than its predecessor at increasing the antibody levels of people older than 55 against the most common version of the virus now circulating.

US federal officials are hoping that the encouraging results will improve what has so far been a dismal public response to the retooled shots. Only about 8 per cent of Americans ages five and older have received the new boosters from Pfizer and Moderna since they were introduced in September.

Pfizer and BioNTech announced the study results in a news release on Friday. The companies said that one month after getting the new booster, clinical trial participants older than 55 had antibody levels that were about four times as high as those who received the original booster. The study measured the levels of neutralising antibodies against two sister subvariants of Omicron known as BA.4 and BA.5.

The number of participants in the study was small, with 36 people older than 55 receiving the new booster and 40 people in that age group receiving the old one. And because the study measured antibody levels only a month after trial participants received the booster, it did not provide any indication about the potential durability of the protection in the longer term.

Results from a similar clinical trial by Moderna on its updated booster are expected as early as next week.

Pfizer’s study also examined the effects of its updated shot on younger adults, although the study did not include a control group that would have allowed for a comparison for that age group between the new booster and the original one.

Pfizer said that the updated shot increased antibodies nearly tenfold for younger adults and 13-fold for older ones, compared with antibody levels before receiving the shot.

United States President Joe Biden’s administration officials said the findings offered a new reason for Americans to seek out the updated shots before what experts fear could be a winter surge of the virus.

But as the pandemic nears the three-year mark, the public seems deeply weary of Covid-19 vaccinations. In a Kaiser Family Foundation survey conducted in September, half of adults said they had heard little or nothing about the new boosters.

The updated shots from Pfizer and Moderna target the original version of the virus as well as Omicron subvariants BA.4 and BA.5. NYTIMES