His statement was intended to challenge the precautions that the agency insisted that vaccinated people take, last month, such as wearing masks and meeting only in limited circumstances with those who did not receive the vaccine.
“Dr. Walensky referred extensively during the interview,” an agency spokesman told the The New York Times. “It is possible that some people who have been fully vaccinated will contract covid-19. There is no clear evidence as to whether they can spread the virus to others. We continue to evaluate the evidence.”
The CDC sought to respond in part to criticism from scientists who noted that recent research is far from sufficient to claim that vaccinated people do not spread the virus.
Data suggests “it is much more difficult for vaccinated people to be infected, but don’t think for a second that they cannot be infected,” said Paul Duprex, director of the Center for Vaccine Research at Pittsburgh University.
In an interview with Rachel Maddow of the NSNBC TV network, Walensky referred to data published by the CDC showing that a dose of Modern or the Pfizer-BioNTech it is 80% effective in preventing infection and two doses are 90% effective.
This would certainly suggest that transmission of the virus by vaccinated persons would be unlikely, but the comments made by the doctor suggested that the protection is complete. “Our data at the CDC today suggests that vaccinated people do not spread the virus, they do not get sick,” she said. “And this is seen not only in clinical trials, but in real-world data.”
The doctor emphasized the importance of people continuing to wear masks and maintaining precautions, even when vaccinated. But his brief comment was interpreted as saying that vaccines offer complete protection against infection or the spread of the virus.
In a pandemic that regularly generates scientific misunderstandings, experts say they understand the doctor and her clear desire that Americans continue to take precautions. It was only on Monday that she declared that the increase in the number of cases left her feeling “an impending doom”.
“If Dr. Walensky claimed that many vaccinated people do not carry the virus, we would not be having this discussion,” said John Moore, a virologist at Weill Cornell Medicine in New York.
“What we do know is that vaccines are substantially effective against infection – and there is more and more data on this – but nothing is 100%,” he added. “It is an important public health message that needs to be understood correctly.”
“Misinterpretation can undermine the agency’s urgent calls for immunization, ‘” experts say. Since Wednesday, 30% of Americans have received at least one dose of a vaccine and 17% are fully immunized.
“There cannot be a visible gap between what the research shows – really admirable but incomplete protection – and how this is described,” said Dr. Peter Bach, director of the Center for Health Policy and Outcomes at Memorial Sloan Kettering Cancer Center in New York. “This opens the door for skeptics who think the government is camouflaging science,” said the doctor, “and totally undermines any argument that people should continue to wear masks after being vaccinated.”
All coronavirus vaccines have been spectacularly successful in preventing serious illness or death from covid-19, but how well they prevent infection is less clear.
Clinical trials have been conducted only to assess whether vaccines prevent serious illness and death. The CDC research, presented on Monday, offered the welcome conclusion that vaccines are extremely effective in preventing infection.
The study covered 3,950 health professionals, first responders and others who have a high risk of infection. Participants performed PCR tests each week and sent the samples to be evaluated, allowing federal researchers to monitor all infections, whether symptomatic or not. Two weeks after vaccination and the vast majority of vaccinees were still free of the virus.
Follow-up data from clinical trials support this conclusion. In the results released by Pfizer and BioNTech on Wednesday, for example, 77 people who received the vaccine contracted covid-19, compared with 850 who received a placebo.
“Clearly, some vaccinated people have contracted the disease,” said Duprex. “We are curbing symptoms, keeping people out of hospitals. But we are not making them completely resistant to infection.”
The number of vaccinees who contracted the infection is higher among those who received vaccines produced by Johnson & Johnson e AstraZeneca, which are less effective, experts say (but these vaccines are also valuable because they uniformly prevent serious illness and death).
Infection rates can be higher among people exposed to a variant of the virus that manages to evade the immune system.
Cases across the country are on the rise again, threatening a new wave. Dr. Walensky’s comment was made the day after she made a touching appeal to the American population to continue taking precautions. “I am asking you to hold on a little longer, to get vaccinated when possible, so that all the people we love are still here when this pandemic is over,” she said.
In view of the increase in infections, it is especially important that immunized people continue to protect those who have not yet received the vaccine, experts say.
“People who have already been vaccinated should not abandon their masks at this time. The pandemic is not over,” said virologist John Moore. / Translation of Terezinha Martino
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