A vaccine breakthrough is defined as a SARS-CoV-2 infection in someone who is fully vaccinated. The U.S. Centers for Disease Control and Prevention’s (CDC) case definition for vaccine breakthrough cases include:

  • A U.S. resident who has SARS-CoV-2 RNA or antigen detected on a respiratory specimen collected 14 days or more after completing all recommended doses of a US Food and Drug Administration (FDA)-authorized Covid-19 vaccine
  • No prior SARS-CoV-2 positive PCR or antigen test in the last 45 days

SARS-CoV-2 breakthrough infections are extremely rare—documented cases generally occur in less than 0.1% of vaccinated individuals—and tend to cause less severe disease than infections in those who have never been vaccinated. Timely information about these infections is crucial to our understanding of the clinical and epidemiological implications of the breakthrough cases. There are many reasons for vaccine breakthroughs, each of which has important and varying implications:

  • A weakened immune system in a vaccinated individual (due to age, medical treatment, or a pre-existing condition)
  • Vaccine degradation (due to improper storage, for example)
  • Waning vaccine-induced immunity (studies on the duration of immunity are ongoing)
  • A viral variant that can bypass vaccine-induced immunity

The CDC reported that between January 1 and April 30, 2021, 10,262 breakthrough infections had been voluntarily reported in 46 U.S. states and territories. Of those infections, 27% were in asymptomatic individuals, 10% of infected people were known to be hospitalized and 2% died.

Sequencing and sharing information about viruses associated with breakthrough infections is a public health priority. Doing so can provide an early warning of the emergence of a known or novel virus variant that can bypass immunity conferred by the vaccines currently in use. This is critical to know early to guide public health guidance and to inform scientists of the need to consider modifying the vaccine formulation or to administer a booster dose of existing vaccine. Of the positive vaccine breakthrough infections that were sequenced to date within the United States, 64% were identified as variants of concern.

Fifteen states currently report vaccine breakthroughs publicly on a regular basis, with varying levels of detail. Nine states report only total numbers and/or the number of vaccine breakthroughs that resulted in hospitalization or death. Our research into US state reporting of vaccine breakthrough cases can be found here.

The best approach to controlling the Covid-19 pandemic is through widespread vaccination. The study of vaccine breakthrough infections is one way to ensure that vaccination is, and will continue to be successful.  By thoroughly investigating viruses that apparently breach the immunity barrier, we can monitor their prevalence and evaluate potential mechanisms for their occurrence. Knowledge of the virus, combined with clinical and demographic information, can be supportive to a better understanding of how the immune status of vaccinated individuals may have contributed to virus evasion of immunity. Linked data to know which vaccine was administered, and when, can further clarify trends that may be associated with specific vaccines to better inform their appropriate use. Importantly,  sequencing breakthrough viruses will show if a vaccine-resistant variant virus is circulating or a new variant is emerging.

Vaccine breakthrough is a rare occurrence, so every bit of information that can be gleaned from such cases will inform scientists about the epidemiology and evolution of the virus. This information would be much more valuable if it were linked to data regarding the vaccination, the lineage of the virus causing the breakthrough, and clinical and demographic information about the infected individuals. Unfortunately, the U.S. health system is ill-suited to connect those dots. States, academic hospitals, and research centers in the U.S. rarely share and aggregate their vaccine breakthrough data, which results in an incomplete picture of the prevalence, spread, and risk associated with emerging variants. This challenge grows exponentially more difficult on a global level.

Coordination requires cooperation, sharing data, and sharing viral specimens. More data is better than less. More connected data is even better. The Covid-19 pandemic is not over, and the availability, transparency, and management of this information is vital to getting the world through this outbreak. Improvements in our global early warning systems will strengthen our ability to detect outbreaks sooner to reduce the risk of another pandemic.

Read the full article about researching vaccine breakthroughs by Jacqueline Houtman, Jessica Malaty Rivera, Dr. Rick Bright,  Lindsey Shultz, and Rebecca Glassman at The Rockefeller Foundation