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.

“These results should be interpreted with caution due to the low counts and the possible biases related to the populations with highest exposure to Omicron (including travelers and their close contacts) which cannot fully be accounted for,” the report said.

Researchers said they believe the booster will be more effective at preventing severe illness.

“There are insufficient severe cases of Omicron as yet to analyze vaccine effectiveness against hospitalization, but this is expected to be better sustained, for both primary and booster doses,” the report said.

Follow the latest news on the Omicron variant with the New York Post’s live coverage

Adam Finn, who is part of the group of experts who advise the UK government, said more research is needed on the variant before they determine whether to give fourth doses.

“We do need to see how things go through this wave and beyond. I think there may well be people who received their boosters early who are in the older, more vulnerable age groups who may need a further jab — that has not been decided yet,” Finn told LBC Radio, Insider reported.