"This is now the most transmissible subvariant we have of all," said Dr. Monica Gandhi, MD, MPH, UCSF Infectious Disease expert and added, "it now looks like it's 30% more transmissible than BA.2 alone."
Dr. Gandhi says that even if you are vaccinated, double boosted and doing everything right this subvariant can still infect you.
"You got a vaccine that looks like the old strain of the virus and there are 32 mutations across the spike protein that omicron has. So, the antibodies which is this defense up here (nasal cavities) don't work as well, but your deep defense down in the lungs and your ability to still protect yourself from severe disease the vaccine still works," said Dr. Gandhi.
RELATED: 100 million Americans could be infected during COVID surge this fall: Here's why
Dr. Bob Wachter, UCSF's chair of medicine, tweeted that his wife, journalist and author Katie Hafner tested positive for COVID-19 after attending a conference. She is vaccinated and double boosted.
"I don't feel great. I have a massive headache," described Hafner.
The couple shared with our sister station in San Francisco KGO-TV why it's important to not let your guard down even if a household member is infected.
"People often assume that one household member has it and the horse is out the barn. Everybody's got it. Don't even be careful. That is just not right. The household attack rate is 40%. So, 40% of people who live in a household of someone who has it will get it. Meaning you have a 60% chance of not getting it," said Dr. Wachter.
VIDEO: Scientists say this key factor could explain why some develop severe COVID and others don't
Dr. Wachter continues to test negative and his wife is expected to recover in the upcoming days. Hafner is taking Paxlovid.
"Within 30 minutes I just feel like I'm chewing metal," described Hafner after taking her first Paxlovid course.
Dr. Gandhi believes a nasal COVID-19 vaccine could prevent future infections.
"A nasal vaccine is going to come. What a nasal vaccine will do is give you antibodies in this area in the nasal cavity and that will prevent you from getting it. So I think that we need to wait for a nasal vaccine to prevent all infections," said Dr. Gandhi.