What breakthrough infections mean for the COVID-19 vaccine

August 25, 2021 | by Jonathan Pinsky, MD
Categories: Healthy Driven Life

The delta variant has resulted in a surge of COVID-19 hospital admissions, largely among unvaccinated individuals.

Ongoing global transmission has resulted in the evolution of variants that can out-compete ancestral variants by their capacity to infect more individuals. The delta variant emerged due to unmitigated transmission through an unvaccinated population.

Because of the high vaccination rates in DuPage County, and strong protection against severe infection and hospitalization, the delta surge has been blunted. The number of patients admitted with COVID-19 at Edward-Elmhurst Health during July and August (during the delta surge) is fewer than during the winter and spring of 2021, and is occurring in predominantly younger age groups that have lower vaccination rates. In contrast, hospitalizations are at record highs in many regions with low vaccination rates.

When fewer persons are vaccinated and there is more infection circulating in the community, the chances of exposure rise. Vaccine breakthrough infections are more likely to occur in communities with low vaccination rates. The best way to prevent vaccine breakthrough infections is by getting more unvaccinated people vaccinated, and to continue a layered approach with masks, social distancing and handwashing.

Do we need boosters?

The delta variant infects more people by making more copies of itself, generating a higher viral load. It takes a higher level of antibodies to neutralize the virus, and the higher level of virus means it takes even more antibodies to neutralize it. In addition, the level of antibodies circulating declines after several months after being fully immunized.

All of these factors result in a drop off in vaccine effectiveness to estimates of 66-88% against delta, 4-6 months after vaccination. Yet, protection has not significantly diminished against severe infection, hospitalization and death, which is still 90-97%.

Those who are fully vaccinated and hospitalized for COVID-19 are more often elderly or immunocompromised. While severe infection requiring respiratory support or death does occur, it is extremely rare.

Though the level of antibodies after vaccination declines with time, memory B cells and T cells are stable. So even if the antibodies don’t stop the infection initially, memory B cells can be triggered to make more antibodies and T cells that can clear viral infected cells, making the infection more often short-lived and mild. This explains the sustained protection against severe infection despite a decline in vaccine effectiveness.

However, there is concern that further decline in vaccine effectiveness with time could result in decline in effectiveness against severe infection, especially in the elderly. There is evidence from Israel that this is the case.

Booster doses for the Pfizer-BioNTech and Moderna vaccines have been tested beginning six months after full immunization and demonstrated a restoration of antibody levels. While more evidence is being collected, the Centers for Disease Control and Prevention has tentatively recommended to start distributing boosters beginning eight months after the second dose of Pfizer or Moderna. Those who received the one-shot Janssen (J&J) vaccine may also need boosters as more studies are forthcoming.

How should fully vaccinated people navigate the surge of Delta variant cases?

It's time to return to a layered approach to protect yourself from COVID-19. While vaccination is the best way to prevent severe illness, hospitalization and death, vaccinated people can add additional layers of protection by masking up indoors and maintaining social distancing.

Higher levels of community vaccination will decrease breakthrough infections. As more people are vaccinated, the virus will have fewer people to infect and spread it. Finally, a tentative plan for additional boosters for those who are fully immunized may add additional protection by restoring circulating antibodies.

Edward-Elmhurst has COVID-19 vaccine appointments available to ages 12 and older. It is easy to schedule a vaccine appointment. You do not need a MyChart account. Schedule your COVID-19 vaccine now.

The information in this article may change at any time due to the changing landscape of this pandemic. Read more about COVID-19.

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