The Covid-19 vaccine, developed by Pfizer and BioNTech, delivers a robust immune response after just one dose, according to a new Israeli study of vaccinated health workers in the country’s largest hospital.
The research, published Thursday in the medical journal The Lancet, followed 7,214 staff members in Israel’s Sheba Medical Center, a government agency that received their first dose of Pfizer-BioNTech vaccination between December 19 and January 24. Medical center scientists found that the vaccine was 85 percent effective in preventing symptomatic Covid-19 within 15 to 28 days after the shot was given.
Experts have warned that more research is needed before broad conclusions can be drawn, but the results do show that robust immunity is generated after one dose and that the second dose can be delayed after the three weeks prescribed by Pfizer to facilitate distribution. . supply constraints.
The timing of the second dose has recently been the subject of debate, and some countries such as the UK have decided to postpone it as a way of accelerating the rate of vaccination in the country. In the United States, where the explosion of the vaccine was bumpy and the winter storms hampered some countries’ ability to administer shots in recent weeks, similar questions have arisen.
Dr. Jonathan Temte, a vaccine expert at the University of Wisconsin’s School of Medicine and Public Health, who was not involved in the Israeli study, said that any comprehensive changes to immunization recommendations needed more information, but that the results of the new study were encouraging. is. .
“It does provide the reassurance that delays for whatever reason, be it the weather or supply chain problems, are comforting, knowing that the individuals who received the one dose do achieve a good level of protection,” he said. he said.
According to the official guidance of the Food and Drug Administration and Pfizer-BioNTech, the two doses should be administered 21 days apart based on the results of clinical trials. For the Moderna vaccine, the only other vaccine currently allowed in the US, the prescribed interval between the two shots is 28 days.
But the vaccine supply is limited and different strains of the virus are circulating across the country, putting pressure on states to vaccinate as many people as possible quickly. Some have questioned whether the timing of the second dose is flexible.
Last month, the Centers for Disease Control & Prevention updated its guidelines to say that the second shot should be administered where possible within the prescribed time frame, but that the second dose of the Moderna and Pfizer-BioNTech vaccines could be delayed to six. weeks, if necessary.
Pfizer said he had not yet studied the changes in timing between doses, and the drugmaker maintained that the health authorities were any deviations from the dosing schedule.
In the new Israeli study, researchers reported 170 Covid-19 infections among health workers at Sheba Medical Center between December 19 and January 24. Of these, 78 people tested positive after receiving the first dose and three individuals tested positive after receiving the second dose. Since the vaccines are not 100 percent effective, it is expected that a small number of people will be able to catch the virus even after they have been fully vaccinated.
The study also found a 75 percent reduction in both symptomatic and asymptomatic infections just after the first shot. The scientists said this reduction suggests that one dose provides a robust enough immune response to justify delaying the second shot.
“Early reduction of Covid-19 rates provides support for delaying the second dose in vaccine-scarce and scarce resource countries, thus enabling higher single-dose population coverage,” the researchers said. written in the study.
However, they recognized that the limitations on the test may have resulted in asymptomatic cases, and that follow-up research is needed to determine the long-term efficacy of a single dose.
The findings provide some of the first real data on the effectiveness of a single vaccine dose. Israel’s vaccination program far surpassed any other country, with more than 30 percent of the country’s 9 million inhabitants receiving both doses.
Temte said that although the early results of Israel’s vaccination program are positive, there are still too many unknowns about the effectiveness of a single dose lasting more than three to six weeks.
“Until that time that there are good clinical trials showing that a single dose provides an equal level of protection, I do not know that we should abandon our approach or draw up new policies,” he said.
It is also not clear how one dose will act against more and more widespread coronavirus strains, including separate strains first reported in the UK, South Africa and Brazil.
“We are walking in an uncharted area,” said Deepta Bhattacharya, an associate professor of immunobiology at the University of Arizona, who was not involved in the study. “The uncertain issue is how long the protection against the current variants will last, as well as some that you might opt for if you wait too long.”
Bhattacharya said it seemed reasonable to postpone the second dose to six weeks, in line with the guidance of the CDC. But beyond that, it can be too soon to know, which means health officials can come up with difficult decisions.
“We reach the limits of what we can see,” he said. “We are currently at a point where we have to make decisions based on imperfect evidence.”
