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  • Writer's pictureP.K. Peterson

COVID-19 Vaccine Breakthrough Infections: What’s the Deal?

“Uninvited guests seldom meet a welcome.” - Aesop

“Uncertainty is an uncomfortable position. But certainty is an absurd one.” - Voltaire

In the U.S., Thanksgiving Day is only a little over a week away. No one wants SARS-CoV-2 to appear as an uninvited “guest” at dinner that day. Every sensible person is doing everything possible to keep this spoiler from ruining this American tradition. Leading the list of preventive strategies is getting vaccinated. Yet, the question on many minds is how much do we need to worry about “vaccine breakthrough infections”? I provide my answer in this Germ Gems post.

What exactly is a “vaccine breakthrough infection?” No vaccine is perfect. Some vaccinated people can develop asymptomatic infections or mild, moderate, severe, and, albeit rarely, even fatal COVID-19 disease. These are called “vaccine breakthrough infections,” which the Minnesota Department of Health defines as “a confirmed or probable SARS-CoV-2 infection [that] occurs 14 or more days after a person has completed all the recommended doses of their COVID-19 vaccine (not including boosters).”

As I’ve mentioned in previous Germ Gems posts, the term “infection” signifies an established relationship between a pathogen (in this case, SARS-CoV-2) and a host (here we’re mainly talking about Homo sapiens, even though we know a growing number of other animal species can be infected). The spectrum of host responses to infection ranges from no illness or symptoms (that is, an “asymptomatic infection”) to mild, moderate, severe, or fatal “disease” (as this word implies the host is provoked or dis-eased).

Although we know asymptomatic infections are very common and that the virus can be transmitted by people with no symptoms, what we care about most is COVID-19 disease. The good news is the currently approved vaccines continue to do well at preventing COVID-19 disease, including hospitalizations, ICU admissions, and mortality. Vaccines not only decrease disease severity, but they also reduce viral transmission rates

In a case-control study of 4,513 hospitalized adults in 13 states with COVID-19 published November 4, 2021 in the Journal of American Medical Association, “Association Between mRNA Vaccination and COVID-19 Hospitalization and Disease Severity,” vaccination with an mRNA COVID-19 vaccine was found to significantly protect against progression to mechanical ventilation and death.

Why do vaccine breakthrough infections occur? The answer to this question boils down to two interacting factors: waning immunity and the increased prevalence of the wily, highly contagious SARS-CoV-2 Delta variant. Several large outbreaks of COVID-19 vaccine breakthrough infections occurred this past summer in association with large public gatherings. These outbreaks afforded an opportunity to study the status of patient immunity to the virus and the risk of COVID-19, caused mainly by the widely circulating Delta variant. Coupled with studies from Israel, where a large majority of the population was vaccinated early on with the Pfizer/BioNTech vaccine, these studies demonstrated a clear waning of immunity—a reduction of neutralizing antibodies to SARS-CoV-2—over time.

In case you’re wondering if you’d be better protected against SARS-CoV-2 infection if you already had a bout of COVID-19 than you would be after vaccination, the answer surprisingly appears to be “no.” That is to say, COVID-19 vaccines create more effective and longer-lasting immunity than natural immunity. Studies show that more than a third of COVID-19 infections result in zero protective antibodies and that natural immunity fades faster than vaccine-mediated immunity. This is why vaccination is recommended, even if you’ve had COVID-19.

Do vaccine breakthrough infections occur with other pathogens? Currently, the Center for Disease Control and Prevention (CDC) recommends that children be vaccinated against 16 different infectious agents. (They are likely to add SARS-CoV-2 [COVID-19] vaccine for certain age groups sometime soon.)

The good news for adults is that the immunity against almost all the pathogens that cause these “childhood infectious diseases” is long-lasting. For adults 50 years-of-age and older, the CDC recommends a tetanus/diphtheria booster (Tdap) that protects against whooping cough as well. Also, to protect against the disease “shingles,” caused by reactivation of herpes zoster virus, the virus that causes chickenpox, the CDC recommends vaccination with Shingrix as a kind of booster. Additionally, adults should be immunized against Streptococcus pneumoniae, a bacterium that causes pneumonia in all age groups.

The only pathogen that’s as troublesome as SARS-CoV-2 in terms of a lack of long-lasting immunity is influenza virus. Like the growing number of SARS-CoV-2 variants, there are more than 100 strains of influenza. Every year the flu vaccine, which is recommended by the CDC for everyone over six-months of age, needs to be modified to include strains that recently emerged. It’s therefore not surprising that developing a “universal vaccine” that would prevent flu caused by all influenza virus strains is a very high priority. The same can be said of the need for a universal vaccine against all coronaviruses.

We have much to be thankful for. As pointed out by Dr. Francis Collins, the director of the National Institutes of Health, “The winter holidays are approaching, and among the many things to be grateful for this year is that nearly 200 million Americans are fully vaccinated for COVID-19. That will make it safer to spend time with friends and family, though everyone should remain vigilant just to be on the safe side.”

COVID-19 vaccine booster shots for all adults could be available as early as tomorrow. New data indicates that everyone should get one immediately. So, if you haven’t already done so, get your booster shot NOW!

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Main Page images courtesy of Shuxian Hu, MD. Dr. Hu is a scientist in the Neuroimmunology Research Laboratory at the University of Minnesota.

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