Current Vaccines vs. SARS-CoV-2 Variants

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Miller School researchers say the Indian variant is the most concerning

As more Americans get fully vaccinated, the immediate threat from COVID-19 is beginning to recede. However, viruses are evolving organisms, making them moving targets for any medical intervention.

Current COVID-19 vaccines show different degrees of effectiveness against the known variants.

“Many people are asking what will happen if we receive a vaccine and encounter one of these new variants — U.K., Brazil, South Africa, India,” said Mehdi Mirsaeidi, M.D., M.P.H., associate professor in the Division of Pulmonary, Critical Care, Sleep and Allergy. “Will the vaccines be effective or not?”

To answer that question, a team of University of Miami Miller School of Medicine researchers, led by Dr. Mirsaeidi, carefully analyzed the relationships between the SARS-CoV-2 spike receptor, the human ACE2 receptor to which it binds, and a neutralizing antibody isolated from a COVID-19 patient (called CV30) that should block those interactions.

Using molecular information from an international database and advanced computational techniques, the group determined that existing vaccines provide ample protection against the U.K. variant, but are less robust against the Brazil, South Africa, and India versions. The study was published May 21 in the journal Viruses.

How the virus propagates

The SARS-CoV-2 virus propagates when the spike protein binds to the ACE2 receptor. The immune system, with or without vaccine support, generates neutralizing antibodies to block this transaction and prevent the virus from inserting its genetic material into cells and creating more viruses.

“The most important things we need to understand about the viral variants are their affinity to the ACE2 receptor, which measures its infectivity,” Dr. Mirsaeidi said, “and whether the antibodies have an affinity for the viral spike protein, so they can neutralize it.”

Using information from the global Nextstrain database, the team analyzed relevant spike protein mutations — from the original Wuhan strain to more contemporary variants in April 2021. While they found the U.K. variant has higher affinity for the ACE2 receptor, and is therefore quite infectious, the neutralizing antibodies also have great affinity for the U.K. spike protein. In other words, current vaccines will be quite effective against it.

The South African strain has less affinity for ACE2, but also has around 30% less affinity for neutralizing antibodies, compared to the original Wuhan virus, making it more resistant but less infectious. At this point, the Indian variant seems to be the most concerning.

Escaping the immune system

“This specific variant has a very low affinity to neutralizing antibodies, as well as high affinity for ACE2,” Dr. Mirsaeidi said. “Which means it has a great chance of escaping the immune system, as well as superior capabilities to get inside cells and infect them.”

Dr. Mirsaeidi cautions that these numbers are not cause for panic but rather motivation to continue aggressively monitoring these variants and accept that, at some point, a vaccine booster may become necessary to handle viral variants.

“India has a large population, over a billion people, and every day they are producing more variants,” Dr. Mirsaeidi said. “We know, because of international travel, that this variant is probably already in the U.S. We will continue to monitor it closely.”

Other Miller School authors included Elena Quinonez, Majid Vahed, Pharm.D., and Abdolrazagh Hashemi Shahraki, Ph.D.

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