An earlier version of this column misstated the reduction in effectiveness for the Moderna and Pfizer vaccines. This version has been updated.

After months of waiting, I finally received my second coronavirus vaccine shot.

It’s not that I’ve procrastinated. Like 15 million Americans, I was initially inoculated with the one-dose Johnson & Johnson vaccine. Since then, I’ve been watching with growing concern as more and more studies emerged that showed one dose of J&J is inferior to the two-dose mRNA vaccines (Pfizer and Moderna).

Fortunately, the Food and Drug Administration has just authorized the second dose of the J&J vaccine for everyone who received the first dose. It is also allowing a “mix and match” approach, such that J&J recipients can receive a Pfizer or Moderna shot as their second dose.

I strongly support this approach. It allows for needed flexibility by local health departments, pharmacies and other vaccine providers to more rapidly administer boosters. It also empowers people to choose based on their preferences and medical circumstances.

All J&J recipients should plan to receive a second shot. A head-to-head comparison published by the Centers for Disease Control and Prevention in September found that vaccine effectiveness against hospitalization was 93 percent for the Moderna vaccine, 88 percent for Pfizer and only 71 percent for J&J.

In addition, protection against symptomatic illness appeared to be waning at an alarming rate among J&J recipients. A new study of more than 620,000 veterans found that J&J’s vaccine effectiveness fell from 88 percent in March to just 3 percent in August. Protection by the mRNA vaccines also waned but not nearly as dramatically as J&J. (Moderna fell from 92 percent to 64 percent and Pfizer from 91 percent to 50 percent.)

J&J reports that a second dose of the vaccine, given two months after the first, would substantially increase protection to 75 percent against symptomatic disease and 100 percent against severe and critical disease. This further supports that the J&J vaccine probably should have been a two-dose vaccine from the start, as many public health experts now believe.

In my case, I would rather not receive a second dose of the J&J vaccine because of the blood-clotting disorder, thrombosis with thrombocytopenia syndrome (TTS), associated with this vaccine. TTS is extremely rare, but it has caused severe illness — and death — in a handful of cases. The group most prone to TTS seems to be women under 50. As a 38-year-old woman, I opted for an mRNA booster because the Pfizer and Moderna vaccines are not linked to TTS.

There are others who might prefer J&J. The mRNA vaccines are associated with another rare condition, myocarditis (inflammation of the heart muscle), that’s most commonly seen in men under 30. It would be reasonable for someone in this group, in consultation with his doctor, to opt for a J&J booster. Similarly, if an individual had a severe allergic reaction to Pfizer or Moderna, a second dose of J&J could be more suitable.

Should people mix and match because it might be more protective than a booster of the same vaccine? Here, the data are less clear. Several research groups have found that mixing one dose of AstraZeneca (a similar vaccine to J&J) with either one dose of Pfizer or Moderna induces a stronger immune response than two doses of the same vaccine. In addition, preliminary results from a National Institutes of Health study showed that while J&J recipients had a fourfold increase in neutralizing antibodies after a second J&J shot, their antibody levels rose 35-fold after a Pfizer booster and 76-fold after Moderna.

As extraordinary as these numbers are, antibody levels are not the only measure of immunity. Moreover, these are limited laboratory studies that are not yet confirmed by real-life comparisons of how well mixing vaccines protects against disease.

My choosing an mRNA second dose is not because it’s necessarily more effective, but because I wish to avoid TTS. My getting Pfizer is purely a practical decision; the Moderna booster is not yet available, and I was not willing to wait any longer.

Frankly, I’ve waited long enough. J&J recipients have been left in the dark for months. Many have taken matters into their own hands to obtain an mRNA shot. Because this wasn’t authorized for J&J recipients — not even for people with severe immunocompromise — they’ve often had to lie and pretend that this was their initial vaccination. Some have been forced to cross state lines. Now, some local pharmacies, like the one I went to, are allowing J&J recipients to obtain a booster, and I expect that nearly all providers will within a week or two, once the CDC follows the FDA with their official recommendations.

A day after my Pfizer shot, I feel great — my only side effect was a slightly sore arm. Above all, I am relieved and thankful to finally receive the additional protection that other J&J recipients and I have known that we need.