Can Vaccinated People Spread the Delta Variant?

While vaccination prevents the transmission of the SARS-CoV-2 virus, all the studies that were carried out to develop the vaccine were done before the Delta variant appeared and spread so rapidly around the world. The data obtained on the transmission of this new strain establish that it could spread more easily among people who have already received the full dose of vaccination.

Vaccinated people and transmission of the Delta variant

According to the Nature report, data obtained from COVID-19 tests in the United States, United Kingdom and Singapore have shown that people who have already been vaccinated can transmit the Delta variant just like the unvaccinated, which contributes to its spread more quickly, increasing the number of infections.

Virologist at the University of Wisconsin-Madison David O'Connor says that people who have the Delta variant can carry a high level of the virus without knowing it, so they can transmit it to other people. This researcher analyzed the infections that occurred in Wisconsin during the months of June and July.

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The results of the researchers' comparisons of the values in 719 people were published on medRxiv. In the study, 90% of the samples studied were of the Delta variant. According to the results, it was determined that 311 vaccinated people were positive for the Delta variant, a large group had the values at a level where the presence of infectious Delta is expected. This was confirmed by culturing 55 samples from people with or without vaccines in which the presence of the virus was detected in almost all of them.

Study co-author Thomas Friedrich (a virologist at the University of Wisconsin-Madison) concludes that vaccinated people can spread the virus, but their relative role in transmitting it in a community is unknown. These data are similar to those published by the Provincetown, Massachusetts CDC. They showed that around three-quarters of new COVID-19 cases were in people who had already been vaccinated. In all cases, the Delta variant was identified.

As a consequence, the CDC recommends that people who are exposed in areas where there is a high probability of transmission continue to wear the masks when they are indoors.

The results obtained in other countries

Studies carried out in Singapore indicate that vaccinated people with the Delta variant can continue to spread the virus for a shorter time than in the case of people who have not been vaccinated. This suggests that, due to the high loads of viruses present in the first week of getting sick with Delta, it is necessary to continue with the measures of mandatory use of masks and correct hand hygiene. This is the best way to reduce infections, regardless of whether you are vaccinated or not, says study co-author Barnaby Young, who is an infectious disease physician at the National Center for Infectious Diseases in Singapore.

In the United Kingdom, a massive analysis of Delta transmission was carried out by Imperial College London, in which the results obtained suggest that in people who were positive for the Delta variant, those vaccinated had a lower viral amount. This confirmation, together with the increase in cases in young people who have not been vaccinated, establish that double vaccination against the Delta variant is effective.

The Delta variant has a different biology

At the Methodist Hospital in Houston, Texas, Delta variants were sequenced and recorded in almost all cases of COVID-19 within the hospital system, finding that almost 17% of the cases of contagion with the Delta had occurred in people already vaccinated. Patients infected with the Delta variant also remained hospitalized a little longer than those infected with the previous variants. This is because this virus has a biology that is slightly different from infection, explains James Musser, who is a molecular pathologist and director of the Research Center for Molecular and Translational Infectious Diseases at Methodist Hospital.

The importance of continuing with protection measures

As a result of the data obtained in the studies, it is vital to continue with the protection measures, that means, wearing protective masks when the person is in closed spaces in order to cut off the transmission process. O'Connor believes that it is necessary to emphasize that vaccines protect against serious complications and death, but do not prevent the transmission of the Delta variant, so it is necessary that after being vaccinated, precautions continue to be taken. The importance of continuing to use the mask to stop the spread of COVID-19 in all its variants is the same if you are exposed to gatherings of many people or in family gatherings. This new strain spreads in the same way in vaccinated people, so you should continue to use the established protective measures.