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A new study out of Israel reignited the public debate Friday about the spacing between the two doses of COVID-19 vaccine, but the U.S. government isn't budging in its commitment to the original schedule.
The Pfizer-BioNTech vaccine might be just as effective if the gap between doses is wider than the recommended 21 days, according to the new study from Israel.
If the doses could be given further apart, more people could be protected faster. Vaccine supplies, which remain quite limited now, are expected to ramp up in late spring.
But government officials want to stick with the dosing schedule that has been scientifically proven to be effective, warning that altering it might weaken the vaccine's effectiveness against variants, or even drive the creation of new variants that escape that protection.
The current schedule provides "an optimal response when you're dealing with variants," Dr. Anthony Fauci, the nation's top infectious disease doctor, said Friday in a news conference.
Studies have shown that vaccines are less protective against some of the newer variants, including one that originated in South Africa, although so far, the vaccines appear to still protect against severe disease and death.
No one knows where the boundary is between lower effectiveness and no effectiveness, which is why, Fauci said, he wants to maintain the regimen shown to be effective in a trial of 44,000 people.
"You want enough of a height of a response that even if you diminish it, you don't diminish it so much to get out of the realm of protection," he said.
Fauci also has said he worries the public will get the wrong message if the gap is extended, believing they can get adequate protection with one shot, instead of two.
"Even though you can get a fair degree of protection after a single dose, it clearly is not durable," he said. "We know that the durability is not as much as the durability that you would get with the boost."
Partial protection from vaccination, he also warned, could lead to more variants, as the virus evolves to skirt around this partial protection. "If you do have a less than optimal response, you could theoretically and inadvertently be selecting immunologically for variants," he said.
The new study from Israel, published as a letter in the journal The Lancet, found that health care workers who received one shot were 75% less likely to get COVID in the 15-28 days after the shot than their unvaccinated peers. They all received a second shot in that time period.
"Our data show substantial early reductions in SARS-CoV-2 infection and symptomatic COVID-19 rates following first vaccine dose administration," the letter concluded. "Early reductions of COVID-19 rates provide support of delaying the second dose in countries facing vaccine shortages and scarce resources, so as to allow higher population coverage with a single dose."
In an email exchange, one of the authors, Dr. Eyal Leshem, director of the Center for Travel Medicine and Tropical Diseases at Sheba Medical Center, said their data on 9,100 healthcare workers isn't useful for determining how much immunity can be provided by a single shot. "In Israel most persons received two doses so these data are unlikely to come from here," he said.
In general, a second vaccination boosts the immune response and adds to the duration of protection.
"The immune response may even be better after a delay, enabling booster shots to enhance and expand the immune response," Barry Bloom, an immunologist at the Harvard T.H. Chan School of Public Health, said during a Friday call with media.
With a first shot, the body makes a mix of different antibodies, Bloom said. A booster expands both the number of those antibodies and their range, likely making the vaccine more effective against different viral variants.
That's particularly important, Bloom said, at a time when we're facing a lot of variants of the original SARS-CoV-2 virus that causes COVID-19.
Increasing the number of antibodies and their duration may be crucial at a time when the variant from South Africa has been shown to reduce the effectiveness of some vaccines.
"Boosters increase the amount (of antibodies), which increases the duration, and even for a variant, would increase to some extent the ability to bind and neutralize," Bloom said. "So giving up a second shot, in my view, is putting people at a risk."
The 44,000-person trial Pfizer and BioNTech ran to determine their vaccine's effectiveness, called for two shots 21 days apart – a relatively short gap designed to speed the testing and get the vaccine out to the public sooner. There was initial concern that the short gap might limit the vaccine's effectiveness, but the 95% efficacy shown in the trial put those concerns to rest.
The U.S. Food and Drug Administration would have to formally approve any change to the dosing schedule.
With some vaccines, a longer gap between shots seems to improve effectiveness. The AstraZeneca-Oxford COVID-19 vaccine for instance, seems to become more effective if the shots are spaced by three months rather than six weeks, according to another Lancet study published Friday.
In that study, researchers looked at the number of confirmed, symptomatic COVID-19 cases in a control group versus the vaccinated group that occurred more than 14 days after the second dose.
Andy Slavitt, the White House senior advisor on the COVID-19 response, speaking at the same Friday news conference as Fauci, said government scientists are keeping track of studies like the one from Israel.
But they do not expect to change government policy based on a single study
"The recommendation from the FDA is two doses, just as it always has been," Slavitt said. "It's important that people understand that we're not going to be persuaded by one study that happens to grab headlines."
In other research out of Israel this week, a national database suggests that the COVID-19 vaccines protect against transmission of the virus, in addition to symptomatic disease.
To save time and make the vaccines available faster, trials have focused on whether the vaccines limited symptomatic disease. They have not looked specifically at whether the vaccines prevent people from passing on the virus, even if they do not develop symptoms from it.
Some vaccines prevent transmission as well as severe disease, while others do not, so it's been an open question. Vaccines that block transmission help cut down disease faster than those that don't, and could bring a faster end to the pandemic.
Contact Karen Weintraub at kweintraub@usatoday.
Health and patient safety coverage at USA TODAY is made possible in part by a grant from the Masimo Foundation for Ethics, Innovation and Competition in Healthcare. The Masimo Foundation does not provide editorial input.
This article originally appeared on USA TODAY: One COVID shot may provide protection, but US stays firm on two doses