The director of the Centers for Disease Control and Prevention, Dr. Rochelle Walinsky, says the recommendation that in some areas of the country immunized people should stick to wearing masks was based largely on troubling research findings.

In a report to the American newspaper "New York Times", writer "Apurva Mandavili" said that new research showed that people who received the vaccination and were infected with the "delta" mutant carry huge amounts of the virus at the level of the nose and throat.

This discovery contrasts with what scientists observed in people who had received vaccinations and were infected with previous strains of the virus, as they seemed to pose no threat in terms of transmitting the infection to others.

This means that people infected with the so-called “penetration infection” - that is, infection with the Corona virus despite receiving two doses of the vaccine - from the delta mutant may transmit the infection just like unvaccinated people, even if they do not show symptoms.

Accordingly, the author indicated that people who have received two doses of the vaccine and live with young children, elderly parents or friends and family members with weakened immune systems will need to be careful, especially in societies where the infection is highly prevalent.

It is still not clear how common a breakthrough infection is and how long the virus remains in the body in those cases.

According to Dr. Walinsky, penetration infections are rare, and unvaccinated people are responsible for the bulk of transmission.

Data reviewed by the Centers for Disease Control and Prevention suggests that people who have received two doses of the vaccine can transmit the virus.

The conclusions are that vaccinated people who have contracted the virus should be tested, even if they feel well (in Britain, for example, vaccinated people who have been in contact with an infected person must self-isolate for 10 days).

The author stressed that the new data does not mean that vaccines are ineffective, as they still prevent the development of the condition of the injured to the worst and death, and people with penetrating infection rarely end up in the hospital.

According to data from the Centers for Disease Control and Prevention, about 97% of people hospitalized with the Corona virus are unvaccinated, but scientists have warned even over the past year that vaccines may not completely prevent infection or transmission (even immunity acquired from Natural infection may provide less protection).

The writer pointed out that previous strains of the virus rarely breached the immunization barrier, which prompted the CDC in May to reassure people who had received the vaccination and inform them that they could refrain from wearing masks indoors, but the usual health rules do not seem to apply to mutated delta.

The writer explained that the delta mutant is about twice as infectious than the original virus, and one study suggested that the viral load in unvaccinated people with the delta mutant may be a thousand times higher compared to what was observed in people who were infected with the original virus.

An expert familiar with the research said CDC data support this finding.

Penetrating infections are becoming increasingly frequent, with many vaccinated people reporting colds, headaches, sore throats, or loss of taste or smell, which are symptoms of an upper respiratory infection.

But the vast majority of infected people do not end up needing extensive medical care because the immune defenses produced by the vaccine destroy the virus before it can reach the lungs.

"We're still seeing a huge impact in disease severity and hospital admissions, and that's really what the vaccine was made for," said Michael Tal, an immunologist at Stanford University.

The writer stated that Corona virus vaccines are injected into the muscles and the antibodies produced by the immune response remain mostly in the bloodstream.

Some antibodies make their way to the nose, which is the main entry point for the virus, but they are not enough to prevent it from moving to the lungs.

"Vaccines are amazingly effective, but they won't give you that natural immunity," says Francis Lund, a viral immunologist at the University of Alabama at Birmingham.

When a person is exposed to any pathogen that infects the respiratory system, the agent finds a suitable environment for reproduction in the lining of the nasal mucosa without causing any harm beyond that.

Dr Michael Marks, an epidemiologist at the London School of Hygiene and Tropical Medicine, said: 'If you walk in the street and take samples from people, you will find people infected with viruses in the mucosa and they do not show symptoms, because our immune system mostly fights these viruses most of the time. ".

The delta mutant appears to develop in the nose, which may explain why more people than scientists expected are experiencing penetrating infection and cold-like symptoms.

But when the virus tries to penetrate the lungs, the immune cells of the vaccinated people flood in and clear the infection quickly before the virus does much damage.

This means that people who have been vaccinated become infected and transmit it in a much shorter period of time than unvaccinated people, says Dr. Lund.

"But this does not mean that they cannot transmit the infection to another person in the first two days of their infection," he added.

In order to stop the spread of the virus, some experts have advocated the use of nasal spray vaccines that would prevent the virus from spreading into the upper airway.

"The first dose of the vaccine should prevent death and admission to hospital, while the second dose prevents transmission. We just need another dose," Dr. Tal said.