Dive Insight:

When the omicron variant was first identified late last year, both Pfizer and Moderna prepared different plans.

Pfizer launched a trial in late January to test whether a vaccine specifically tailored to omicron would perform better than a second booster against the evasive and fast-spreading variant. Moderna quickly followed with one study evaluating an omicron-targeting shot and another testing both the variant and the virus’ original strain.

None of those studies have produced results yet. In the meantime, pressure has is mounting to tighten the U.S.’s defenses against the next COVID-19 surge. While infections and hospitalizations have plummeted in the U.S., an omicron “subvariant” has begun spreading across Europe amid relaxed mitigation measures and waning protection from boosters. Early warning signs, through wastewater samples, have indicated a similar rise could soon follow in the U.S.

That combination of factors has led Pfizer and Moderna to jump ahead of their trials and instead rely on observational studies to support requests to authorize another shot. Both of them have cited two analyses from Israel that point to lower rates of infection and severe COVID-19 as well as a higher immune response in people who have received four shots instead of three.

However, the results of those studies are mixed, with one showing a fourth shot wasn’t strongly protective against mild or asymptomatic infections. That’s made it hard to tell how much of the general population may benefit from another booster.

Once again, Pfizer and Moderna are charting different courses. Pfizer has asked the agency for a narrow authorization in people 65 and older, a group most vulnerable to severe illness and death from COVID-19. Moderna seeks a broader clearance in all adults who have previously received a booster. The idea is to let the Centers for Disease Control and Prevention, as well as healthcare providers, “determine the appropriate use” of an additional booster dose, such as for those at higher risk of COVID-19 because of their age or underlying health status, Moderna said.

Moderna hasn’t said when to expect results from the continuing studies of its omicron-targeting vaccines.