NEW BRUNSWICK, N.J. — Johnson & Johnson says a booster shot of its COVID-19 vaccine appears to produce “a rapid and robust” increase in antibodies needed to fight the coronavirus.

The drugmaker says researchers saw an increase in antibodies nine-fold higher than levels seen about a month after the first dose of the vaccination was administered. The company cited early results from studies looking at people who received the booster after getting an initial dose of J&J’s single-shot vaccine.

J&J says researchers saw increases in antibodies in people ages 18 to 55 and in study participants 65 and older who received a lower booster dose.

U.S. health officials announced last week plans to dispense COVID-19 booster shots to all Americans to shore up protection amid the surging delta variant of the virus. Officials say the protection against infections wanes over time among various vaccines but remains strong at preventing hospitalizations and deaths.

J&J says it is talking with regulators in both the U.S. and Europe about booster shots.