A breakthrough COVID infection refers to an individual testing positive for SARS-CoV-2, the virus that causes COVID-19, after they have been fully vaccinated. This means they have received all recommended doses of an authorized COVID-19 vaccine and at least 14 days have passed since their final dose. It indicates that despite vaccination, the virus has managed to “break through” the immune protection.
What is a Breakthrough COVID Infection?
A breakthrough infection is an expected part of vaccination campaigns. Vaccines significantly reduce the risk of severe illness, hospitalization, and death, but do not offer 100% protection against infection. Therefore, encountering the virus after vaccination can still lead to a positive test, even if the illness is mild or asymptomatic. This highlights that while vaccinated individuals are much less likely to get sick, infection can still happen.
Why Breakthrough Infections Occur
Breakthrough infections can occur for several reasons. Initial mRNA vaccine trials showed effectiveness around 94-95%. Immune protection provided by vaccines can also wane over time, as antibodies may decrease, making individuals more susceptible to infection.
The emergence of new viral variants, such as Omicron, also contributes. These variants may have mutations that allow them to evade some immunity from original vaccines. Omicron, for example, is significantly more transmissible than earlier variants like Delta, increasing exposure and infection risk. Individual variations in immune response also play a role, as some people, particularly older individuals or those with weakened immune systems, may not develop as robust an antibody response.
Symptoms, Severity, and Prevalence
Symptoms of a breakthrough infection are generally similar to those in unvaccinated individuals, but are often milder and of shorter duration. Common symptoms include fever, fatigue, sore throat, dry cough, headache, muscle aches, and sometimes a temporary loss of taste or smell. While vaccinated individuals can still experience these, they are significantly less likely to develop severe illness, require hospitalization, or die from COVID-19. For instance, one study found that among breakthrough cases, 27% were asymptomatic, 10% required hospitalization, and 2% resulted in death.
The prevalence of breakthrough infections has varied, with some studies showing low rates, such as less than 0.2% among those who received both vaccine doses in one U.K. study. Incidence can increase with highly transmissible variants like Omicron. In New York State, as of May 2023, approximately 19.1% of fully vaccinated individuals had a laboratory-confirmed breakthrough case, but hospitalizations among this group were much lower, at about 0.81%.
Managing a Breakthrough Infection
If you suspect or confirm a breakthrough COVID infection, it is important to get tested, either with a PCR test or a rapid antigen test. If your test result is positive, you should isolate yourself at home to prevent further spread of the virus. Current guidelines suggest isolating until your symptoms improve, you have been fever-free for at least 24 hours without fever-reducing medication, and at least five days have passed since your symptoms began.
You should contact your doctor for guidance on symptom management and to determine if antiviral treatments are suitable for you. Antiviral medications like nirmatrelvir plus ritonavir (Paxlovid) and molnupiravir are available for individuals at high risk of severe illness, and these treatments are most effective when started soon after symptoms appear. Rest, hydration, and over-the-counter medications like acetaminophen for fever and body aches can help manage symptoms. Continuing public health precautions such as wearing a high-quality mask when around others and maintaining physical distance are also recommended, especially until at least day 11 after symptom onset or a positive test.