A year ago, when the United States decided to go big on vaccines, it bet on nearly every horse, investing in a spectrum of technologies. The safest bets, in a way, repurposed the technology behind existing vaccines, such as protein-based ones for tetanus or hepatitis B. The medium bets were on vaccines made by Johnson & Johnson and AstraZeneca, which use adenovirus vectors, a technology that had been tested before but not deployed on a large scale. The long shots were based on the use of mRNA, the newest and most unproven technology.
The protein-based vaccines have moved too slowly to matter so far. J&J’s and AstraZeneca’s vaccines are effective at preventing COVID-19—but a small number of recipients have developed a rare type of blood clot that appears to be linked to the adenovirus technology and may ultimately limit those shots’ use. Meanwhile, with more than 180 million doses administered in the U.S, the mRNA vaccines have proved astonishingly effective and extremely safe. The unusual blood clots have not appeared with Pfizer’s or Moderna’s mRNA technology. A year later, the risky bet definitely looks like a good one.
The U.S. has ordered enough mRNA vaccines to inoculate its entire population. In that context, the CDC and FDA’s call to pause the J&J rollout this week is a blow to the American inoculation campaign, but hardly a devastating one. (J&J’s vaccine accounts for less than 5 percent of doses administered so far, and AstraZeneca’s has not yet been authorized in the U.S.) But the rest of the world has been banking on the J&J and AstraZeneca vaccines, which are both cheaper and easier to distribute because they don’t require the same cold storage as mRNA vaccines. If the blood-clot risk is real, the divide between the mRNA-vaccine haves and have-nots will only grow. The U.S. will be fine; the rest of the world will face difficult questions about balancing the risks and benefits of an affordable, good-but-not-best vaccine against a disease that has killed nearly 3 million people.