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Will the COVID-19 vaccines encourage the emergence of new variants or immune evasion?

Biology/Immunity Vaccines

A: No. Vaccines REDUCE opportunities for viral replication needed for variants to emerge.

➡️ TL;DR: The virus has more opportunity to replicate in unvaccinated populations, creating a FAR bigger risk for the development of SARS-CoV-2 mutations.

Even so, the good news is that the emergence of variants that fully evade vaccine induced immunity is considered unlikely.

If you’ve heard about antibiotic resistance, you might wonder why the same evolutionary pressure might not lead SARS-CoV-2 to evade vaccine induced immunity. Most scientists do not consider this a likely scenario. Why not? Vaccines work differently from therapeutic drugs such as antibiotics. While antimicrobial resistance is common, vaccine resistance is rare.

Important differences:

➡️ Vaccines tend to work prophylactically (preventing infection and initial replication) while drugs tend to work therapeutically (resolving existing infection that has already undergone extensive replication).

➡️ Vaccines induce immune responses against multiple targets on a pathogen while drugs tend to target very few. Thus, a pathogen has fewer chances to develop a mutation that completely evades vaccine immunity.

💥 To evolve resistance, you need mutations– which requires replication. When a vaccinated person is exposed to a pathogen, infection might not occur at all.

➡️ No infection=no replication=no mutations.

Sometimes initial infection and replication in a vaccinated person does happen. But when this happens the vaccinated immune system has a huge head start stopping the virus, so the virus replicates MUCH less compared to an unvaccinated person starting their fight from scratch.

➡️ Less replication= less opportunity for mutations.

❓But if the vaccines all target the spike protein, isn’t this a vulnerable target that could be evaded by potential mutation? Luckily not.

The spike protein of SARS-CoV-2 is not just one target for your immune system. The protein comprises 1273 amino acids, and the immune system can target short stretches of them, giving it MANY targets. To escape immunity, a large fraction of them would need to change via mutation. T cells can target almost the entire spike protein, and we know that the variants don’t seem to impact T cell effectiveness.

So far, the most successful variants owe their success to better *transmissibility* rather than immune evasion. While Beta and Gamma show greater immune evasion in lab studies, Alpha and Delta have consistently outcompeted them in real life. This is likely because even if a variant can evade some neutralizing antibody response, it still mostly hits a dead end in vaccinated individuals. Thus, it is increased transmission in the *unvaccinated* that has allowed Alpha and now Delta to become dominant and cause huge outbreaks—not Beta and Gamma spreading among the vaccinated.

So, if evolution of vaccine resistance is so unlikely, what are we worried about?

➡️ Many people are still unvaccinated, and vaccines don’t protect 100%. As Delta shows, a variant that spreads more easily can be very bad news.

BOTTOM LINE:

💥 Vaccines prevent viral replication.
💥 Less replication= less opportunity for mutations.
💥 Vaccine induced immunity is multi-faceted and robust to variants.
💥 Vaccinating the world is the best way to slow the emergence of new variants.

Love,
Those Nerdy Girls

Further reading:

This post was partially adapted from threads from Edward Nirenberg and Dr. Angela Rasmussen.

“Why does drug resistance readily evolve but vaccine resistance does not?”

“Concerns about SARS-CoV-2 evolution should not hold back efforts to expand vaccination”

T cells and variants

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