Would a delayed second dose of the Covid-19 vaccine end the pandemic sooner?

The race to beat the coronavirus variants, and to get as many people vaccinated as quickly as possible has intensified a debate in the scientific community about what the best strategy is to end the pandemic.

The question at the heart of the debate: would delaying a second dose of the Pfizer and Moderna Covid-19 vaccine get more people protected more quickly?

People who push for this approach say it wouldn’t cause any harm and it would take those vaccines that states reserve for second doses and get them out now, as opposed to making people wait for a first dose.

With a steady supply, people should easily be able to get a second dose, just with more weeks in between, they argue.

For opponents of the idea – including scientists who lead the Biden administration’s pandemic efforts – it’s a gamble that could, in fact, spread more dangerous variants and not provide the best protection the vaccines offer.

How this debate plays out could change the trajectory of the Covid-19 pandemic and potentially change when some people can get a vaccine.

Currently, the US is vaccinating people at an average of 3.1 million doses a day. That’s five times faster than the global average. That may sound like a lot, but still only 19% of the population is fully vaccinated, according to the US Centers for Disease Control and Prevention.

At the same time, the US has seen a sixth straight week of increases in cases, according to the CDC, which says the spread of the more transmissible B.1.1.7 variant is in part to blame.

There is more vaccine supply than there was in early January, but vaccine appointments are still hard to come by in some parts of the country.

To get more people vaccinated, countries including the UK delayed the second dose of the two-dose Covid-19 vaccines. While the US Food and Drug Administration authorized the Pfizer and Moderna vaccines using a double dose, a CDC study found that just a single dose provided 80% protection. With a double dose it’s over 90% — and recent studies show that protection lasts at least six months and maybe longer.

A January editorial published in the Annals of Internal Medicine explained the reason for the delayed dose strategy this way: “A single-dose SARS-CoV-2 vaccine approach deals directly with the shortage of vaccines by vaccinating twice the number of people while maximizing the probability of achieving herd immunity.”

The math is pretty simple, Dr. Michael Osterholm, the director for the Center for Infectious Disease Research and Policy at the University of Minnesota, said.

If you have two people in a room and you give one person two doses they get 90% protection, but the other person gets none. Give each a single dose, in three weeks they both have 80% protection.

“Right now, with the surge that’s about to occur, this is what we want to do right now,” Osterholm told CNN Monday. “Get as many people protected as we can so they don’t get severe illness and hospitalizations and death.”

Dr. Atul Gawande, a member of the Biden administration’s coronavirus transition team, and a surgeon who works at the Harvard’s School of Public Health, said that behavioral measures alone aren’t going to be enough to curb the spread, especially in places seeing surges like in the Midwest and Northeast.

“In these areas where we are having a surge, vaccine appointments go in minutes,” Gawande said. “We need to be vaccinating a lot more people.”

Gawande had been on the fence about it, but as more contagious variants have spread, he started to think a delayed second dose would protect the population more quickly. He said many more people in these areas will need to be vaccinated to bring an end to the surge. The strategy would also reduce the number of variants.

Dr. Ashish Jha had been calling for the delayed second dose strategy for months, but the Dean of Brown University’s School of Public Health now thinks it may be too late.

“By the end of May we’re going to have more vaccines than arms for them to go into,” Jha told CNN Monday. “I don’t know that strategy has quite the same value as it did before.”

Unless something changes with the supply, Dr. Kent Sepkowitz, an infectious disease specialist at Memorial Sloan Kettering Cancer Center in New York, agrees.

“If the stockpile is running low, than yeah, I think we ought to prioritize ‘pretty good’ vaccination for more people than ‘super duper’ protection for the fewer,” Sepkowitz told CNN Monday. “If, however, the vaccine supply isn’t so sparse, than I think we ought to plow ahead with what we’re doing.”

The Biden administration is not on board with delayed second doses. The vaccines weren’t tested that way, and even if studies show one dose provides protection, it’s still a gamble.

“We have been concerned, and still are, that when you look at the level of protection after one dose, you can say is 80%, but it is somewhat of a tenuous 80%,” said Dr. Anthony Fauci, the direction of the National Institute of Allergy and Infectious Diseases. “When you just leave it at one dose, the question is, how long does it last?”

Variants may also diminish the effectiveness of the vaccine and that means, “you’re in a tenuous zone if you don’t have the full impact,” Fauci said.

Fauci fears that partly vaccinated people could get infected and the viruses in their bodies, rather than being stopped completely, could start mutating — giving rise to even more new variants.

“Right now, given the number of vaccines we’re able to give every day, literally every day that goes by, we get closer and closer to where we want to be,” Fauci said. “For that reason, although we always continue to keep an open mind, we consider the route that we’re on now is the best route.”

Dr. William Schaffner, an infectious disease specialist at Vanderbilt University, said with so much supply at this point in the pandemic, the more effective strategy may be to concentrate on on helping the hesitant get vaccinated.

“The eager beavers, the early acceptors, they’re still coming in, but we’re getting to the end of that group,” Schaffner said. “We’re now reaching out to the people who are more skeptical that they need the vaccine.”