MIAMI (CBSMiami) — The global COVID-19 death toll has topped 4 million, as the Centers for Disease Control and prevention tracks a surge in the number of Delta variant cases.

The CDC says cases of the highly transmissible Delta variant is the dominant strain in the country and makes up 51.7% of all COVID-19 cases.

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It is also fast becoming the dominant strain in South Florida and that has Florida International University Infectious Disease Specialist Dr. Aileen Marty concerned for several reasons.

“Florida’s vaccination rate is not high enough for Herd Immunity,” said Dr. Marty in an email conversation with “Immunity from having had COVID-19 is not long-lived nor as specific or valuable as vaccine immunity, and thus, natural immunity cannot be “added” to vaccine immunity to produce significant Herd Immunity,” said Dr. Marty.

She added, “We have a very few inducements to the use of other public health measures in Florida; thus people’s behaviors are promoting the spread of infection.”

She is also concerned because the Delta variant is “far more contagious and produces more severe disease, behaviors that drive transmission also drive the production of newer and potentially more dangerous variants, and our cases are rising.”

Andy Slavitt, a former senior adviser to President Joe Biden’s COVID response team said Wednesday, “”We should think about the Delta variant as the 2020 version of COVID-19 on steroids.  It’s twice as infectious. Fortunately, unlike 2020, we actually have a tool that stops the Delta variant in its tracks: It’s called vaccine.”

For fully vaccinated people, the variant “presents very little threat to you, very unlikely that you’re gonna get sick,” he explained.

However, there is an upward trend in COVID-19 cases in South Florida, according to weekly reports released by the Florida Department Health and that is because the number of people receiving vaccines appears to be dropping.

The current surge of cases is troubling to experts who say everyone should still be protecting themselves with situational awareness.

“Continue to avoid large, crowded indoor spaces (especially poorly ventilated spaces) with unknown vaccine status persons. Continue to use all reasonable public health measures as appropriate,” said Dr. Marty.

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The increasing prevalence of new coronavirus variants is raising questions about how well protected those who’ve already had their COVID-19 shots are against evolving forms of the SARS-CoV-2 virus.

Dr. Marty says COVID-19 booster shots would be helpful.

“Ideally, we would get COVID-19 boosters, especially those who received less effective vaccines.  Unfortunately, on a world-scale, fully vaccinated persons are only at ~12% (and many received inferior inactivated forms of the vaccine). This leads to a moral dilemma between giving citizens of wealthy nations maximum vaccine protection but leaving citizens of LMIC nations stranded.”

But how will you know whether you need a booster shot?

“You don’t know. While it is possible to do tests that would identify your humoral (antibody) and cellular immunity, which would suggest if you need a booster, these tests are costly and invasive,” she explained. “There is no current recommendation to do these tests. However, if you are elderly or immunocompromised, there is data indicating that quite likely, you did not develop the highest levels of immunity from the vaccination cycle, and a booster may be indicated.”

If you are immunocompromised, she said, “Check with your doctor about the type of immunocompromised condition you have and how it may or may not be associated with your level of protection.”

She added the type of booster does not necessarily need to match your first shots.

“Data shows you can mix and match but check with your doctor.”

So what is the status of COVID-19 in Florida?

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“It is difficult to tell at times because Florida stopped providing that information directly to the public, however, the CDC continues to track it but not on daily basis and its data shows Florida is doing poorly compared to the rest of the country,” said Dr. Marty.