According to internal documents from the US CDC, people who have been vaccinated can still contract the Delta variant and pass it on to others, prompting officials to make new recommendations.
The document, presented at a meeting of the Centers for Disease Control and Prevention (CDC) in late July, documents the agency’s efforts to convince the public to vaccinate and self-prevent the virus. The CDC believes that Delta has changed the battle with Covid-19.
According to the report, Delta is more easily transmitted from person to person than the virus that causes Ebola or the flu. Dr. Rochelle Walensky, director of the CDC, said that vaccinated people infected with the Delta variant carry large amounts of the virus in their nose and throat. This is different from previous versions of the virus, when the person who injected the vaccine was almost unable to spread the disease to the community.
However, the new discovery does not mean the vaccine is less effective. Vaccines still help prevent patients from becoming serious and dying. Breakthrough nCoV infections very rarely require hospitalization. About 97% of new Covid-19 cases are in unvaccinated people.
Vaccinated people sometimes report headaches, sore throats, and loss of taste or smell – symptoms of an upper respiratory infection similar to Covid-19. But most don’t need to be hospitalized, because the antibodies and T cells from the vaccine destroy the virus before it enters the lungs.
Dr. Michal Tal, of Stanford University’s immunology department, said: “The vaccine will still have a very, very large impact on the number of severe cases and hospitalizations. That is its mission.”
The CDC says previous versions of the virus rarely cross the immune barrier. But Delta is a completely different story. The variant is twice as contagious as the original virus. Research shows that the amount of virus in unvaccinated people infected with Delta is thousands of times higher.
On the other hand, high levels of the virus cause some people to break through the infection. However, when the nCoV tries to invade the lungs, immune cells increase, quickly eliminating the pathogen before it wreaks havoc on the body. Thus, vaccinated people will contract nCoV in a much shorter time than the unvaccinated group, according to Dr. Frances Lund, an immunologist at the University of Alabama, Birmingham.
“But this means that during the first few days of illness, they can still pass the virus on to others,” she added.
To prevent the virus from entering the area, experts support the development of an inhaled vaccine to prevent pathogens from the upper respiratory tract. “Vaccine version 1.0 prevents hospitalizations and deaths. Version 2.0 should block transmission of the virus. We need to keep repeating the research process,” said Dr. Michal Tal.
The CDC’s findings have a major impact on efforts to contain the transmission. Recently, experts have recorded a number of cases of breakthrough nCoV infection, that is, getting sick after being vaccinated for 14 days or more. In these patients, the Delta variant is as contagious as an unvaccinated person, even if they have no symptoms.
Families with young children, elderly parents or immunocompromised relatives need to be vigilant, especially when living in an outbreak area. Vaccinated Americans may still have to wear masks, not only to protect themselves but also those around them.
On average, the US has about 67,000 new infections every day, the possibility that vaccinated people carry the Delta variant drives the number up.
The data in the CDC study related to the epidemic cluster in Provincetown, Massachusetts, where the July 4 National Day festival took place, causing 882 people to be infected with nCoV. Nearly three-quarters of them are fully vaccinated. They also monitor the situation from professional sports leagues through the Covid-19 Sports and Society Workgroup. The federation tests more than 10,000 people a day and sequenced all of the virus samples.
It is not clear how common the breakthrough infection is and how long the virus stays in the human body. The condition is rare, and unvaccinated people are still the main cause of outbreaks, Dr. Walensky said.
Research by the CDC shows that people who have been vaccinated are still attacked by the virus. “On an individual level, this is why we’re updating our recommendations,” says Dr. Walensky.
Experts suggest that vaccinated people should still be tested if exposed to F0. In the UK, vaccinated F1, F2s are still required to self-isolate for 10 days.
Thuc Linh (Follow NY Times, Washington Post)