“It’s not that you don’t have good immunity,” she said. “Then, instead of having serious illness, you may have some symptoms of runny nose and upper respiratory tract symptoms - before you kick start your immune system and fight it,” she said. This strategy, which uses T cells, kills the virus. Once a host is infected with the virus, a different arm of the immune system is deployed, said UC San Francisco infectious disease expert Dr. If there are fewer antibodies, the virus wins. If there are more antibodies that can bind to the virus, the antibodies win - and fend off the virus, he said. It’s a competition between the immune system and the virus, he said. Joel Ernst, professor of medicine and chief of the Division of Experimental Medicine at UCSF. When multiplying, delta cranks out so many new virus particles that sometimes a few of them escape our protective troops, called antibodies, said Dr.

“It’s definitely a harder virus to stop.” “Delta is just incredibly more infectious than the original virus,” said Crotty. The challenge is that delta behaves differently. For instance, data shows that six months after inoculation, protection from the Pfizer vaccine dropped only slightly, from 94% to 91%, he said. The problem is not that protection from the vaccine is weakening, said virologist Shane Crotty of the Vaccine Discovery Division at La Jolla Institute for Immunology. “Unlike the Alpha variant that we had back in May, where we didn’t believe that if you were vaccinated you could transmit further, this is different now, with a delta variant,” Walensky said. In the past, vaccinated people who became infected were found to have greatly reduced levels of virus, suggesting little danger that they would pass it on.īut more recent research of delta-driven clusters of cases has revealed that levels of virus are nearly equivalent in both vaccinated and unvaccinated people, said Walensky. Vaccines are 79% to 95% protective against the delta variant, according to an assortment of international studies.īut the ascendance of the delta variant, which spreads much more readily than earlier strains, has changed our understanding of the risk of transmission. That means they’re also less likely to become infected and transmit it. Masks are especially important in high-risk regions, and vaccinated people who are visiting children, the immunocompromised or the unvaccinated should wear them, she said.Īlthough daily case rates are rising in some highly vaccinated Bay Area counties, the overall case rate remains low here, so vaccinated people are less likely to be confronted by someone with the virus. People with “breakthrough infections - rare as they are - have the potential to transmit at the same capacity as an unvaccinated person,” she said. Because of the virulence of the delta variant, the unvaccinated can no longer count on protection from people who have gotten the shots. Walensky said at a Tuesday press briefing. Unaware that they are infected, vaccinated people are inadvertently infecting others, Centers for Disease Control and Prevention director Dr. Masks, again? Vaccines were supposed to protect us.įaced with the threat of the highly contagious delta variant and startling new evidence that vaccinated people can spread COVID-19, the CDC is following in California’s footprints, urging us to once again to mask up.

Vaccinated people transmit virus