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Breaking Down Breakthrough Infections

October 4, 2021

In the last few months, the discussion around the COVID-19 pandemic has focused largely on the spread of the more contagious delta variant, which is now the dominant strain of the virus here in New York City and across the country.

In addition to the rapid spread of the delta variant among those who are unvaccinated, we have seen an increase in something else you may be hearing about: breakthrough cases.

What is a breakthrough case?

Put simply, a breakthrough case is when a fully vaccinated individual gets COVID-19. In technical terms, a vaccine breakthrough infection is defined as a positive molecular (PCR or NAAT) or antigen test in a respiratory specimen collected from a person 14 days or more after either a second dose of the Pfizer or Moderna vaccine, or a single dose of Johnson & Johnson’s Janssen vaccine.

It is important to remember that no vaccine is 100% effective, meaning that vaccine breakthrough cases are always to be expected. All COVID-19 vaccines currently authorized in the U.S. have been shown in clinical trials as well as real-world results to be highly effective at preventing COVID-19 and complications such as hospitalization and death.

So even when there are breakthrough infections, as can be expected with any vaccine, all authorized COVID vaccines in the U.S. are highly effective at preventing severe illness, hospitalization and death. In other words, they offer significant protection against the worst outcomes of COVID-19.

In addition, the data show that those who do get breakthrough infections fight off the virus more quickly than those who are unvaccinated and are likely infectious to others for a shorter period of time than an unvaccinated case.

How common are breakthrough infections?

While breakthrough infections have been increasing since the significantly more contagious delta variant became dominant in the U.S., from what we have learned so far, it appears that only a small percentage of fully vaccinated individuals have gotten breakthrough infections. According to the NYC Department of Health, from when the first vaccinations started offering protection in NYC on January 17, 2021 to September 18, 2021, unvaccinated persons are 5 times more likely to become infected with COVID-19 in NYC.

When it comes to the severity of infection, however, the data is actually quite overwhelming. Unvaccinated individuals account for the vast majority of COVID hospitalizations and deaths across the country. According to data from the NYC Department of Health from January 17, 2021 to September 18, 2021, unvaccinated New Yorkers are 9 times more likely to be hospitalized because of COVID complications.

Areas of the U.S. with the lowest vaccination rates are experiencing the most significant increases in infections as well as severe stress on their health care systems. Alarmingly, in some states, cases, hospitalizations and deaths have now surpassed all previous highs. This only appears to be happening in areas of the country with lower vaccination rates.

As we are confronted with heartbreaking news from around the country, every New Yorker can recall the pain of last spring and summer, when our own ICUs were at capacity and every day was another grim milestone of loved ones lost.

But thanks to the effectiveness of the vaccines and our high vaccination rates — as well as our world-class contact tracers — NYC is not experiencing the kind of surge in cases and hospitalizations seen in other parts of the country.

Do breakthrough cases mean the vaccines aren’t working against the delta variant?

The evidence of hospitalizations and deaths cited above actually shows that the vaccines ARE working. With each passing day, it becomes clearer that the COVID-19 vaccines are very effective at achieving their intended goals: preventing severe illness, hospitalization and death.

Studies that have been conducted thus far back up the real-world evidence we are seeing on a daily basis: being fully vaccinated offers clear protection from the most severe effects of COVID-19.

This is a reminder that getting vaccinated is more important than ever.

Does this mean vaccinated people can also transmit the virus?

Yes. Those who are fully vaccinated and get infected can spread the virus to others. Scientists are currently studying additional effects.

However, as mentioned above, vaccinated individuals appear to be infectious for a shorter period of time than those who are unvaccinated.

The highly contagious nature of the delta variant and the ability for anyone infected with it, whether they are vaccinated or not, to transmit it, make isolating if you have COVID and quarantining if you are both unvaccinated and have been exposed to someone with COVID absolutely crucial to stopping the spread of the disease.

How are breakthrough cases tracked in NYC, and who is at risk for them?

The NYC Health Department identifies breakthrough infections by matching case data to immunization data in the Citywide Immunization Registry (CIR). Cases that are hospitalized or die are reported to the Centers for Disease Control and Prevention (CDC).

Both agencies have been working to identify patterns in patient characteristics (such as age or underlying medical conditions), which vaccine was received and which variant the patient was infected with. To date, no unexpected patterns have been identified in the case demographics or vaccine characteristics among reported breakthrough infections.

Staying informed

The latest information on breakthrough infections in New York City can be found on the NYC Health Department’s COVID-19 webpage. On the COVID-19: Data page, you will find weekly rates broken down by vaccination status, as well as Breakthrough Infection FAQs.

Below are some additional resources:

Centers for Disease Control and Prevention

The Possibility of COVID-19 after Vaccination: Breakthrough Infections

COVID-19 Vaccine Breakthrough Case Investigation and Reporting

Interim Public Health Recommendations for Fully Vaccinated People

COVID data tracker

World Health Organization (WHO)

Vaccine efficacy, effectiveness and protection

Staying safe

As explained above, two critical reasons behind New York City’s relative success in combatting COVID-19 are the effectiveness of the vaccines and the city’s high vaccination rates. These have helped prevent us from returning to the dire situation we were in last year and when every day was another immeasurable tragedy of lost loved ones.

Another reason NYC is not seeing the same kind of surges in COVID-19 cases and hospitalizations that are overwhelming cities and states around the country is the NYC Test & Trace Corps. We have made testing and vaccination free and widely accessible, including offering these services at home for any and every New Yorker who wants them. Additionally, we offer services that make it easier for people to isolate or quarantine such as a free hotel stay and Take Care packages with personal protective equipment for a household of three that is enough for ten days. Our contact tracing workforce, which has served the city proudly and with distinction since June of 2020, has been tireless in its efforts to stop the spread of COVID-19 in New York City. In fact, NYC’s contact tracers have engaged with over one million New Yorkers who were identified as being in close contact with someone who had COVID-19.

Today, as we watch other parts of the country suffer increasing COVID-19 cases, hospitalizations and deaths, each and every one of us must be steadfast in our resolve to stay New York Strong by doing everything we can to stop the spread of this virus.

WNYC Test & Trace therefore asks all New Yorkers to be our partners in fighting this pandemic by:

  • Getting vaccinated
  • Becoming a vaccine champion—help your family, friends, colleagues and neighbors understand how crucial vaccination is to stop the spread of COVID-19 in our communities
  • Sharing reliable, factual, science-based information such as that found on the CDC and NYC Health Department websites
  • Enabling exposure notifications on your smart phone to know if you’ve been exposed to COVID-19—or exposed someone else
  • Answering the call if a contact tracer calls you

If you have been in close contact with someone who tests positive for COVID-19, they may provide Test & Trace with your information so a contact tracer can reach out to you to let you know you’ve been exposed and provide you with resources and information on what you should do next.

A call from an NYC contact tracer will come from one of the following: “NYC Test & Trace Corps,” “NYC COVID Test,” 212-540-#### or 212-242-####. If you want, you can ask to validate your tracer. They’ll give you a code to type into testandtrace.nyc to prove who they are.
Participating in the contact tracing process is one of the most important things you can do to help stop the spread of COVID in your community and your city. So please, if you see a call from one of the above caller IDs, answer the call!

And remember: The best and easiest way to protect you, your loved ones, your community and your fellow New Yorkers from COVID-19 is to get vaccinated.

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