In about six months, proposals for modified vaccines aimed at omicron subvariants became reality. Here's a timeline from the waning efficacy of older COVID-19 vaccines to when inoculations began.
April 6: The FDA's Vaccines and Related Biological Products Advisory Committee met to discuss the next plans for combating COVID-19, but no specific action was promoted as the members said data would become clearer in the summer.
April 22: After two years of the coronavirus mutating and the number of breakthrough infections rising, researchers found that authorized COVID-19 boosters were less effective at preventing hospital admissions.
May 9: Senior Biden administration officials warned the U.S. would not be able to afford next-generation COVID-19 vaccines unless more funds were approved.
June 8: After finding a "superior" response in its omicron-focused booster candidate, Moderna CEO Stéphane Bancel predicted the vaccine would be approved and distributed by late summer.
June 22: Moderna said it was already manufacturing millions of its not-yet-authorized new doses as the leading omicron subvariants BA.4 and BA.5 increased from accounting for 2 in 10 COVID-19 cases to more than 3 in 10.
June 25: Pfizer, Moderna and Sanofi-GSK were among the drugmakers furthest in the race as they reported promising results from late-stage clinical trials.
June 28: On the same day BA.4 and BA.5 became the slight majority for causing all reported U.S. COVID-19 cases, an FDA advisory panel recommended vaccine manufacturers develop modified boosters.
June 30: The FDA officially told vaccine-makers to focus on BA.4 and BA.5, which were nicknamed "sister variants."
July 11: Moderna said its omicron-focused booster candidate was nearly twice as effective as its original formula against BA.4 and BA.5.
July 25: Days after infectious disease experts warned Americans not to wait for the new booster, White House officials said the administration was focusing on new shots and aimed to have them in arms by mid-September.
July 26: BA.5 quickly surpassed BA.4, with the former accounting for nearly 82 percent of infections and the latter making up 12.9 percent.
July 29: Pending approval from regulatory agencies, the U.S. bought 66 million doses of Moderna's omicron-tweaked boosters.
Aug. 24: Within two days of each other, Pfizer and Moderna submitted applications to the FDA to authorize their respective bivalent boosters — which were part original booster and part omicron strain — for emergency use.
Sept. 1: The FDA and CDC signed off on authorizing Pfizer's and Moderna's updated boosters as hospitals prepared for the rollout.
Sept. 21: For a few days, health systems and pharmacies ran out of Moderna's omicron-specific boosters. The FDA then cleared a few batches from a facility not authorized to manufacture the modified vaccine Sept. 27.
Sept. 26: Moderna and Pfizer submitted applications for their pediatric boosters.
Sept. 30: The CDC revised its "up to date" vaccination term to include the primary series and the recently authorized omicron-targeting booster. The rollout at the time was slow, with less than 2 percent of the eligible population receiving the new shot — possibly because half of the population said they knew little or nothing about omicron boosters in a survey.
Oct. 3: New variants gained traction as the prevalence of BA.5 plateaued.
Oct. 5: A report found that the new boosters could prevent 745,000 hospitalizations.
Oct. 12: The FDA and CDC authorized Pfizer's and Moderna's omicron-targeted boosters for children as young as 5.
Oct. 13: Pfizer said its bivalent booster was safe and effective among adults.
Oct. 14: New COVID-19 variants and subvariants are "splintering."