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The Covid-19 vaccine developed by Pfizer and BioNTech produces a robust immune response after a single dose, according to a new Israeli study of health workers vaccinated at the country’s largest hospital.
The research, published Thursday in the medical journal The Lancet, followed 7,214 staff at Israel’s Sheba Medical Center, a government facility, who received their first dose of Pfizer-BioNTech vaccination between December 19 and January 24. the medical center found the vaccine to be 85% effective in preventing symptomatic Covid-19 within 15 to 28 days of receiving the vaccine.
Experts have warned that more research is needed before general conclusions can be drawn, but the results provide evidence that robust immunity is generated after one dose and that the second dose could be delayed beyond the three weeks prescribed by Pfizer to facilitate distribution and supply constraints.
The timing of the second dose has been the subject of much debate recently, with some countries such as the UK choosing to delay it in order to speed up the country’s vaccination rate. In the United States, where the vaccine rollout has been bumpy and the winter storms of the past week hampered the ability of some states to deliver vaccines, similar questions have emerged.
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 any drastic changes to vaccination recommendations would require more data , but that the results of the new study are encouraging. .
“It reassures that delays for whatever reason, whether it’s the weather or issues in the supply chain – it gives some comfort in knowing that people who have received the single dose are achieving a good level of protection. “, did he declare.
Official guidelines from the Food and Drug Administration and Pfizer-BioNTech state that the two doses should be administered 21 days apart based on the results of clinical trials. For Moderna vaccine, the only other vaccine currently authorized in the United States, the prescribed interval between the two injections is 28 days.
But vaccine stocks are limited and different strains of the virus are circulating across the country, pressuring states to quickly vaccinate as many people as possible. Some wondered if there was any flexibility in the timing of the second dose.
Last month, the Centers for Disease Control and Prevention updated their guidelines to state that the second vaccine should be given on time when possible, but the second dose of Moderna and Pfizer-BioNTech vaccines could be delayed. up to six. weeks, if necessary.
Pfizer said it had not yet studied changes in the timing between doses, and the drugmaker argued that any deviation from the dosage schedule is up to health officials.
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 people tested positive after receiving the second dose. Since vaccines are not 100% effective, it is expected that a small number of people can contract the virus even after being fully vaccinated.
The study also found a 75% reduction in symptomatic and asymptomatic infections after the first stroke. Scientists said these reductions suggest that one dose provides an immune response robust enough to justify postponing the second shot.
“Early reductions in Covid-19 rates allow second dose to be delayed in countries facing vaccine shortages and limited resources, so as to allow higher population coverage with a single dose,” the researchers wrote in the study.
They recognized, however, that testing limitations may have resulted in an undercount of asymptomatic cases and that follow-up research is needed to assess the long-term efficacy of a single dose.
The results provide some of the first real data on the effectiveness of a single dose of vaccine. Israel’s immunization schedule has far exceeded any other country, and more than 30 percent of the country’s 9 million people have already received both doses.
Temte said that while the initial results of Israel’s vaccination program are positive, there is still too much unknown about the effectiveness of a single dose beyond three to six weeks.
“Until there are good clinical trials that show that a single dose provides an equivalent level of protection, I don’t know if we should abandon our approach or create new policies,” he said. declared.
It is also unclear how one dose will work against different strains of coronavirus that are becoming more prevalent, including separate strains that were first reported in the UK, South Africa and Brazil.
“We are facing uncharted territory,” said Deepta Bhattacharya, associate professor of immunobiology at the University of Arizona, who was not involved in the study. “The uncertain question is how long this protection will last against the current variants, as well as some of those that might be selected if you wait too long.”
Bhattacharya said delaying the second dose for up to six weeks, per CDC guidelines, seems reasonable. But beyond that, it may be too early to tell, which means health officials may be faced with tough decisions.
“We are pushing the boundaries of what we can see,” he said. “We are sort of at a point where we have to make decisions based on imperfect evidence.”
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