The development of the Covid-19 vaccines happened with great urgency, for obvious reasons.
One of the timesaving techniques by Moderna and Pfizer involved scheduling the two vaccine doses fairly close together — just three or four weeks apart — during the research trials. The companies did not test multiple gaps between the two shots to see which was the most effective. They each chose a short gap to finish the trials as quickly as possible.
The decision made a lot of sense. It allowed the U.S. mass vaccination program to start in December, rather than pushing it back a few months. Many lives have been saved as a result.
But the approach means that nobody knows what is the most effective gap between the two shots. Maybe it really is three to four weeks. Maybe a longer delay is just as effective (or, for that matter, even more effective).
And the short delay does come with a large downside.
The U.S. is choosing to give millions of people a second shot while making millions of others wait for their first. That’s happening even though a single shot provides a high degree of protection and even as a more severe, contagious coronavirus variant is sweeping the country. Both cases and hospitalizations have risen in recent days, and deaths have stopped declining.
are calling on the Biden administration or governors to change policy and prioritize first doses:
“We’ve missed a window, and people have died,” Sarah Cobey of the University of Chicago told my colleague Carl Zimmer.
“Getting as many people as possible a vax dose is now urgent,” Dr. Atul Gawande, the surgeon and medical writer, tweeted.
“We need to get more people vaccinated,” Dr. Ezekiel Emanuel of the University of Pennsylvania told me.
In a USA Today op-ed, Emanuel, Govind Persad and Dr. William Parker argue that spreading out the first and second shots would be both more equitable and more efficient. It’s more equitable because working-class, Black and Latino communities all have lower vaccination rates, which means that first shots disproportionately now go to the less privileged and second shots go to the more privileged. It’s more efficient because a delay in second shots would allow the country to double the number of people who receive a first shot in coming weeks.
Doing so could prevent other states from experiencing the current misery in Michigan, where a severe outbreak fueled by the B.1.1.7 variant has overwhelmed hospitals. In much of the South and the West, the variant is not yet as widespread.
Britain’s better results
The biggest worry about a longer delay between shots is that it may allow a new variant to develop in people while they are waiting for their second shot and do not yet have full protection. Dr. Anthony Fauci, the top Biden administration adviser, opposes a longer delay largely because of this possibility.
But it remains only a theoretical possibility, as Dr. Catherine Schuster-Bruce, a British health care writer, has noted. There is no data showing that variants are more likely to develop in people who have received only one shot, just as there is no data showing that a three- or four-week gap between shots is ideal.
There is real-world evidence — from Britain — showing large benefits from maximizing the number of people who get one shot.
total shots per capita. The difference is that Britain has deliberately delayed second shots, by up to 12 weeks. The results are impressive.
Despite being the country where the B.1.1.7 variant was first detected, Britain now has the pandemic under better control than the U.S. does. Both cases and deaths have fallen more sharply, highlighting the power of a single vaccine dose. “The levels of antibodies after the first shot are sky-high,” Dr. Robert Wachter of the University of California, San Francisco, told me.