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Boosters and Breakthrough Cases

Of the 63.7% of people in the US who are fully vaccinated, less than half have received their booster shot. This proportion is also true in Colorado where 68% of the population has been fully vaccinated while less than half have gotten boosted. The demand for boosters shots has also slowed despite the rapid rise in cases resulting from the new Omicron variant. While both the White House and the CDC have advocated for booster shots, about 85 million eligible Americans have not received their booster and 63 million eligible Americans have yet to receive any dose of a COVID-19 vaccine.


Breakthrough Cases: What they mean and why they happen

Breakthrough cases are COVID-19 cases that occur in fully vaccinated people. There were fewer when Delta was the prominent variant; however, with the rapid spread of Omicron, these instances have become far more common. The most important factor in why breakthrough cases happen is the emergence of new variants. Originally, the COVID-19 vaccines were created with the first variant (Alpha) in mind as that was what was mainly circulating at the time. Given that the current dominant variant (Omicron) is around 3 to 4 times more infectious than Delta, the antibodies produced from vaccination might be less effective. The vaccines weren’t specifically targeted at these new variants so their effectiveness (mostly against infection) is less now than it was earlier in the pandemic.


Additionally, no vaccine is 100% effective. For instance, the flu vaccine is typically somewhere between 40% and 60% effective at preventing infection. Some early studies in the UK suggested that COVID vaccine boosters were 70% to 75% effective at preventing symptomatic infection with Omicron.


Why get boosted? What difference will it make?

The purpose of a booster shot is to increase protection after the initial immune response from the previous vaccine dose has waned. The amount and quality of antibodies are improved after a booster dose. The extra shot allows immune cells to react which improves immune system response. Recently released studies (focused on the Moderna and Pfizer mRNA vaccines) found that those who have been boosted are significantly more protected against severe disease during the circulation of the Omicron variant. Receiving the booster reduced the risk of an ER or urgent care visit by 82%. Comparatively, in those who were not boosted and 6 months or more out from their second dose, the vaccine was only 38% effective at reducing that risk. The booster also was 90% effective at preventing hospitalization with Omicron compared to 57% effective for those who were not boosted and 6 months or more out from their second dose.


In an interview with The Harvard Gazette, Jonathan Abraham, an assistant professor of microbiology at Harvard Medical School, speculated that continued periodic boosters may be necessary for the next few years to protect against potential new strains of COVID-19. Other vaccines (not just those that protect against COVID-19) also require boosters. For example, Tdap immunization (which protects against tetanus among other things) is boosted every 10 years.


Who should get boosted? What if I already had COVID?

There is no official CDC guidance on getting boosted after contracting COVID-19. However, several experts say that getting boosted after ending isolation is beneficial as “people develop different levels of immunity following a COVID infection” and the duration and strength of that immunity is still unknown. A booster would provide more predictable immunity than an infection.


The CDC recommends that everyone aged 12 and over who received an mRNA vaccine (Moderna or Pfizer) should get a booster shot 5 months out from their second dose. For those who originally received a Johnson and Johnson vaccine, the CDC recommends an mRNA booster 2 months after the original vaccination.

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