News has been circulating about Covid-19 breakthrough cases. But what exactly is a breakthrough case, and how many are happening locally?

Breakthrough cases are Covid-19 cases that develop after a person has received full vaccination against the virus. In the U.S., the FDA issued emergency authorization for the use of Pfizer, Moderna and Johnson & Johnson vaccines, which are proven to reduce the risk of hospitalizations and death from Covid-19. According to the Centers for Disease Control, more than 161 million Americans have been fully vaccinated as of July 19, 2021. The consensus from the CDC and health professionals nationwide is that vaccination is the first line of defense and can significantly reduce the severity of your case if you do contract Covid.

And while rare, breakthrough cases are occurring. During the same time period, the CDC received reports from 49 U.S. states and territories of 5,914 patients with Covid-19 breakthrough infections who were hospitalized or died.

Locally, Sarasota Memorial Hospital has admitted some breakthrough cases, too. On Saturday, July 24, infectious disease specialist Dr. Manuel Gordillo wrote in a Facebook post that, out of 187 Covid-19 inpatient admissions during the month of July, 17 patients were vaccinated. Of those 17, 10 had moderate symptoms and seven were asymptomatic but were hospitalized for other medico-social problems. As of Thursday, July 28, there are 95 Covid-19 positive patients at the hospital and 23 positive cases in the ICU.

Dr. Gordillo answered some of the community's questions about the delta variant and breakthrough cases in a video for the hospital on Wednesday, July 21.

What are the current Covid-19 case numbers at SMH?

"Three to four weeks ago, we saw the beginning of a new surge. This escalated within the last two weeks, with our Covid cases going from three to the upper 30s in the hospital. [As of July 28, there are 95 Covid-positive patients in the hospital.] Initially, we only had one or two patients in the ICU. This same trend is happening across the state."

Is the delta variant the reason for the increase in cases?

"There's a convergence of issues. Delta drives the whole thing, because it is more transmissible than the other variants. If a more transmissible variant is introduced to a population, it is going to target the unvaccinated. The other big factor is behavioral. We have more mobility in the population; we are interacting and meeting indoors more frequently. When you get into a crowded environment without masks on, that's a recipe the virus loves. Another factor is seasonality. In Florida, seasonality is a little different—as the weather gets hotter, people go indoors, which drives the opportunity for the virus to spread."

Who are the people being hospitalized with Covid-19? Are some of them vaccinated?

"Since the beginning of January, when vaccination began, the majority of people coming into the hospital with Covid have been unvaccinated. These are not exact numbers, because things change a little bit, but not too long ago we had one case. This is why we are saying the pandemic is becoming one of the unvaccinated."

"In the outpatient setting, there are more breakthrough cases, but they're milder. Some people who are vaccinated pick up the virus but are asymptomatic, or have flu-like illness. The severe disease is largely occurring in unvaccinated folks."

If you have a breakthrough infection, are you still able to pass Covid-19 to others?

"The answer is unclear. You probably can, but it's much less probable. The chances are markedly attenuated, and the reason is because people that are vaccinated have less viral load, or amount of the virus in the nose and mouth—sometimes by 1,000 times or more. So the virus is less likely to be transmissible."

"We've learned this lesson with HIV and Hepatitis-C and other viruses. When there's little virus in the blood, you are not contagious. The same thing happens with respiratory viruses: the less virus in the nose and mouth, the less contagious you are going to be."

Are most breakthrough infections the delta variant? Why is this the case?

"Viruses evolve and have mutations, and the mutations out-compete each other. Delta, in particular, is more fit than other variants. It doesn't take long for it to displace other strains. We have the U.K. variant—the predominant one in Florida—and then we have the Brazilian one and the Indian one, or delta strain."

"At this point, when we have all three competing in Florida, delta is predicted to out-compete all others. Just about every [case] out there is delta. While we don't sequence, or test, all cases, health professionals have done studies, projections and modeling. Just about everything is delta."

"Remember, 60 percent of adults in Sarasota County are vaccinated, so it's bound to happen. For example, in places like Israel, where 100 percent of the population is vaccinated, breakthroughs are occurring because there is nobody else to spread it to."

Will there be Covid-19 booster shots to prevent these breakthrough cases?

"For immunocompromised people, it will probably be fairly soon. Five percent of the U.S. population is immunocompromised, whether due to an organ transplant, chemotherapy, certain immune deficiencies or AIDS. Those folks are going to need boosters at some point in the near future.

"For the general population, it's really uncertain what's going to happen. We've heard that Pfizer applied for a booster, but the FDA and CDC have already said the evidence is not meeting the threshold for a booster. These groups have several cohorts studying folks, testing them from time to time to see if their infection rate is higher than expected at that time."

"We need to see a higher incidence of infection among vaccinated people than what is expected in order for a booster [to be approved], and so far, we are not seeing that."