Will They Transmit the Virus? Scientists Say They Do Not Know.
Researchers reacted angrily after the head of the Centers for Disease Control asserted that vaccinated people “do not bear the virus.”
The Centers for Disease Control and Prevention retracted controversial statements made by its director, Dr. Rochelle P. Walensky, on Thursday, claiming that people who are vaccinated against the coronavirus never contract the virus or spread it to others.
The assertion cast doubt on the measures the agency had urged vaccinated people to take only a month earlier, such as wearing masks and congregating with unvaccinated people only in limited circumstances.
“During this interview, Dr. Walensky spoke freely,” an agency spokesperson told The Times. “It is possible for individuals who are completely vaccinated to contract Covid-19. The proof is inconclusive as to whether they are capable of spreading the virus to others. We are still analyzing the evidence.”
The agency was reacting in part to criticism from scientists who acknowledged that existing evidence does not support the argument that vaccinated individuals cannot transmit the virus.
The data show that “it is much more difficult for vaccinated people to become infected, but do not assume for a moment that they cannot become infected,” according to Paul Duprex, director of the University of Pittsburgh’s Center for Vaccine Research.
Dr. Walensky cited data released by the Centers for Disease Control and Prevention showing that one dose of the Moderna or Pfizer-BioNTech vaccine was 80 percent effective at preventing infection and two doses were 90 percent effective at preventing infection in a television interview with MSNBC’s Rachel Maddow.
This indicated that transmission from vaccinated individuals was highly improbable, yet Dr. Walensky’s remarks implied that safety was full. “Our evidence from the Centers for Disease Control and Prevention today shows that vaccinated people do not bear the virus and do not get sick,” she said. “And that this is true not only in clinical trials but also in real-world data.”
Dr. Walensky continued by stressing the importance of continuing to wear masks and taking care, including for those who have been vaccinated. Nonetheless, the brief remark was generally interpreted as implying that vaccines provided full protection against infection or transmission.
In a pandemic prone to scientific confusion, experts expressed sympathy for Dr. Walensky and her apparent wish for Americans to continue taking precautions. It was only Monday that she shared a sense of “impending doom” due to her increasing caseload.
“Had Dr. Walensky stated that the majority of vaccine recipients do not carry virus, we would not be having this discussion,” said John Moore, a virologist at New York’s Weill Cornell Medicine.
“What we do know is that vaccines are extremely effective against infection — there is increasing evidence for this — but nothing is 100 percent effective,” he added. “This is a critical public health message that must be delivered correctly.”
According to some experts, misinterpretation could jeopardize the agency’s urgent appeals for vaccination. As of Wednesday, 30% of Americans had received at least one dose of a vaccine, while 17% had received all three doses.
“There can be no contradiction between what the study demonstrates — truly remarkable yet imperfect safety — and how it is described,” said Dr. Peter Bach, director of the Memorial Sloan Kettering Cancer Center’s Center for Health Policy and Outcomes in New York.
“This gives credence to critics who believe the government is sugarcoating the science,” Dr. Bach said, “and totally undermines any remaining justification for continuing to wear masks after vaccination.”
Although all of the coronavirus vaccines are highly effective at preventing severe disease and death caused by Covid-19, the extent to which they avoid infection has been unclear.
The vaccines’ clinical trials were performed primarily to determine whether the vaccines prevent serious illness and death. The Centers for Disease Control and Prevention announced Monday that vaccines are still highly successful at preventing infection.
3,950 health care professionals, emergency responders, and those at high risk of infection were enrolled in the report. Each week, participants swabbed their noses and sent samples for testing, allowing federal researchers to keep track of all illnesses, whether symptomatic or not. The study discovered that the vast majority of vaccinated individuals stayed virus-free two weeks after vaccination.
Clinical study follow-up results corroborate this result. According to findings released Wednesday by Pfizer and BioNTech, 77 people who received the vaccine developed coronavirus infection, compared to 850 people who received a placebo.
“Clearly, some vaccinated individuals do contract the disease,” Dr. Duprex said. “We’re putting an end to symptoms and getting patients out of hospitals. However, we are not making them totally immune to infection.”
Experts believe that the number of vaccinated people who contract the disease would be higher than those who receive vaccines manufactured by Johnson & Johnson and AstraZeneca, which have a lower efficacy. (However, some vaccines are still worthwhile, since they consistently prevent serious illness and death.)
Infection rates can also be higher in individuals exposed to a virus variant that is immune-evading.
Cases across the country are once again on the rise, indicating the possibility of another boom. Dr. Walensky’s statement comes just one day after she made an emotional plea to the American public to maintain precautions.
“I’m pleading with you to just hang in there a little longer, to get vaccinated as soon as possible, so that all of the people we care for can still be here when this pandemic is over,” she said.
Given the rising numbers, it is important that those who have been immunized against the virus continue to protect those who have not been, experts said.
“Vaccinated individuals should not discard their masks at this time,” Dr. Moore said. “This pandemic is far from being over.”