Despite the alarming spread of the Delta variant and the Center for Disease Control and Prevention’s renewed recommendation that the fully vaccinated again wear masks indoors in areas with higher rates of transmission, one thing about COVID-19 has not changed.

If you’re fully vaccinated, you have very little risk of serious illness, hospitalization or death from the coronavirus.

An accurate assessment of breakthrough cases, when someone fully vaccinated becomes infected, remains elusive because of inconsistent tracking. But the CDC, through July 19, received reports of 5,914 COVID-related hospitalizations among the nation’s 161 million-plus fully vaccinated people. That means only 0.004 percent of the fully vaccinated later became seriously ill or died from COVID-19.

The state Department of Public Health reported, as of Wednesday, 1,133 confirmed COVID-19 cases among the fully vaccinated — less than 0.06 percent of the 2 million people vaccinated in the state. The unvaccinated account for almost all COVID-19-related hospitalizations. People 75 years old and up have accounted for close to 54 percent of hospitalizations and and 80 percent of the deaths among the state’s breakthrough cases.

A new CDC report says the Delta variant spreads as rapidly as chickenpox and more easily than the common cold, the 1918 flu and smallpox. The agency also cited a recent Cape Cod outbreak, where  both vaccinated and unvaccinated people had similar levels of virus in test samples. Previous studies indicated the fully vaccinated were less likely to spread the virus. This new information adds urgency to vaccinate those who remain hesitant.

“If you do get the vaccination, your chance of dying or being hospitalized are extremely, extremely low,” says Dr. Ajay Kumar, Hartford HealthCare’s Chief Clinical Officer. “It’s worse if you don’t get the vaccination.”

Despite the apparent protection against serious illness among the fully vaccinated, limited tests of vaccines against the Delta variant  have produced inconsistent results. In the most encouraging lab test, the Pfizer-BioNTech vaccine was 88 percent effective against Delta after two shots — a drop from 93.7 percent against previous COVID-19 strains. At that level of effectiveness, the United States could expect 88 percent fewer Delta cases compare to a no-vaccination baseline.

Another study in Israel, however, found the Pfizer-BioNTech vaccine only 64 percent against Delta. The Moderna vaccine was 72 percent effective against Delta after one dose in another lab study.

These results have led to some speculation that people might need a booster shot, depending on the vaccine. Pfizer released data this week that antibody levels quintupled among people 18 to 55 years old and by 11 times among those 65 to 85 who received booster shot. But health officials await additional studies before recommending a booster shot.

“We don’t have the answer to that yet,” says Dr. Virginia Bieluch, Chief of Infectious Diseases at The Hospital of Central Connecticut in New Britain. “For some people, especially those who are older, have underlying medical problems or those whose immune systems aren’t working well, boosters may well be indicated in the near future. There are some data that some patients with compromised immune systems do get an added boost from a third injection of one of the mRNA (Pfizer or Moderna) vaccines.”