Johnson & Johnson said Wednesday that early- to mid-stage clinical trials in patients who had previously received a single dose of its Janssen pharmaceutical arm’s vaccine, which relies on a different kind of technology than the more commonly used Pfizer/BioNTech and Moderna mRNA-based COVID jabs, demonstrated a robust immune response. Interim study data showed the level of antibodies that bind to the coronavirus’s cell-infiltrating spike protein was nine times higher in participants who got a second J&J dose compared with the antibody levels in people 28 days out from receiving just the initial one-dose immunization, according to the company.

That could prove critical for individuals who got the Johnson & Johnson jab eight or more months ago since its effectiveness wanes over time and there’s been persistent scrutiny of its relatively lower effectiveness compared with Pfizer’s and Moderna’s vaccines. All three companies say (and available study data has shown) their vaccines remain effective at preventing serious illness, hospitalizations, and COVID-related deaths even as Delta variant-linked cases soar, although preventing infections and illness that doesn’t send you to the hospital is a more nuanced matter.

Still, this is the first set of booster-related data produced by Johnson & Johnson and the company plans to submit it to the FDA alongside additional trial information which emerges in the coming weeks and months. The agency could then authorize a second dose of the vaccine for those who have already received one, as it has for Moderna’s and Pfizer’s mRNA vaccines for a limited pool of immune compromised Americans, and they could begin being distributed as early as the week of September 20 should the Biden administration get its way. The administration announced an aggressive immunization plan last week recommending all adults eight months out from a second Pfizer or Moderna dose should receive a third as a booster, although final clearance would have to come from the FDA and the Centers for Disease Control (CDC).

That plan, as well as the FDA’s booster authorization for a small sliver of immunocompromised individuals such as organ transplant recipients earlier this month, was silent on what people who received the Johnson & Johnson jab should do in the absence of sufficient data.

“We have established that a single shot of our COVID-19 vaccine generates strong and robust immune responses that are durable and persistent through eight months. With these new data, we also see that a booster dose of the Johnson & Johnson COVID-19 vaccine further increases antibody responses among study participants who had previously received our vaccine,” said Janssen R&D head Mathai Mammen in a statement. “We look forward to discussing with public health officials a potential strategy for our Johnson & Johnson COVID-19 vaccine, boosting eight months or longer after the primary single-dose vaccination.”

There are still outstanding questions for Johnson & Johnson vaccine recipients. For instance, existing studies of treatments similar to J&J’s suggest an even more effective strategy than a second dose is to boost this particular jab with an mRNA vaccine from Pfizer or Moderna. Leana Wen, a physician who’s been critical of what she sees as a relative lack of information and urgency for the J&J crowd, wrote that she’s still holding out for the mix-and-match method in a Wednesday Twitter thread.

To that end, the National Institutes of Health (NIH) and numerous academic partners have begun such mix-and-match vaccine trials the include the Pfizer, Moderna, and Johnson & Johnson COVID shots. Data from those trials could begin to emerge in September and shift public health leaders’ and regulators’ approach to boosters. A pandemic requires constant data monitoring as the situation on the ground changes and we find out more about a pathogen, its variants, and how they interact with existing vaccines. At the very least, more than 14 million Americans now have at least some information, if not official government recommendations, about the prospect of additional J&J vaccine doses.

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• What Pfizer’s FDA approval means for Americans and businesses
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