The effectiveness of Pfizer’s booster shot against symptomatic Omicron significantly wanes after 10 weeks, a new study said this week — as experts weigh whether fourth shots are necessary.

The UK Health Security Agency said those who had received three doses of Pfizer’s vaccine saw their protection against symptomatic illness caused by the variant drop from 70 percent to 45 percent within 10 weeks, according to a report released Thursday.

Researchers then compared that to people who had gotten the two-dose Pfizer vaccine then received a Moderna booster shot. For up to nine weeks, they retained around 70 to 75 percent protection, though not many people in the study received the regimen, which could impact the findings.

Other factors should also be considered when weighing the overall results of the study, health officials said.