Until last June, the cumulative data from the C.D.C. showed that immunization with the Moderna vaccine resulted in the lowest rates of breakthrough infections; those who got Johnson & Johnson saw the highest rates, with Pfizer-BioNTech somewhere in the middle.

During the summer months, the gaps — particularly between J. & J. and Pfizer — began to narrow. By now, all the vaccines seem to be performing about equally well against coronavirus infections; in fact, Johnson & Johnson appears to be holding up slightly better.

As of Jan. 22, the latest data available, unvaccinated people were 3.2 times as likely to become infected as those who received the single-dose Johnson & Johnson vaccine; they were 2.8 times as likely to become infected as those who received two doses of the Moderna vaccine and 2.4 times as likely as those with two doses of Pfizer-BioNTech. Overall, then, the Johnson & Johnson vaccine appeared to be somewhat more protective against infection than the two alternatives.

Among Americans who got booster doses, all the vaccines appeared to have roughly the same effectiveness against infection. A booster shot did not add much to Johnson & Johnson’s previous level of protection (although the data do not indicate who received which type of booster shot).