A single-dose COVID vaccine presented an alternative approach to immunization, offering a simplified vaccination schedule. The development of such a vaccine sought to offer a convenient option for individuals to gain immunity against the virus.
Overview of Single-Dose COVID Vaccines
The Janssen COVID-19 Vaccine, developed by Johnson & Johnson, was a single-dose vaccine. It received an Emergency Use Authorization (EUA) from the U.S. Food and Drug Administration (FDA) on February 27, 2021, for individuals 18 and older. Its single-dose design aimed to simplify vaccination and accelerate global immunization.
How They Work
The Janssen vaccine employs viral vector technology to deliver genetic instructions to the body’s cells. It utilizes a modified, harmless adenovirus, a common cold virus, as a vehicle. This adenovirus cannot replicate in humans. The adenovirus carries the genetic code for the SARS-CoV-2 spike protein.
After the vaccine is administered, the adenovirus enters human cells, where it releases the genetic instructions for the spike protein. The body’s cells then read these instructions and produce copies of the spike protein. The immune system recognizes these foreign spike proteins and begins to develop antibodies and T-cells specifically targeting them. This prepares the body to recognize and fight off the actual SARS-CoV-2 virus if it encounters it in the future, thereby providing protection against COVID-19.
Level of Protection Offered
Clinical trial data indicated that the Janssen single-dose vaccine provided a notable level of protection against COVID-19 outcomes. Approximately 28 days after vaccination, the vaccine was 66.3% effective in preventing symptomatic COVID-19 in clinical trials. This efficacy was observed across different geographic regions, including the U.S., Latin America, and South Africa.
The vaccine demonstrated even higher effectiveness against severe outcomes of the disease. It was 85% effective in preventing severe COVID-19, and offered complete protection against COVID-19-related hospitalization and death 28 days post-vaccination. While initial protection was observed, booster doses were later recommended to enhance and prolong immunity, especially against emerging variants. For individuals who initially received the Janssen vaccine, a booster dose of an mRNA vaccine was generally preferred.
What to Expect After Vaccination
After receiving the single-dose vaccine, individuals commonly experienced temporary side effects, which typically resolved within a day or two. These included pain, redness, or swelling at the injection site. Systemic side effects often reported were fatigue, headache, muscle aches, and fever. These reactions are normal signs that the body is building protection.
A rare but serious adverse event associated with the Janssen vaccine was Thrombosis with Thrombocytopenia Syndrome (TTS), involving blood clots with low platelet counts. This condition was very rare, occurring in approximately 3.8 cases per million doses administered. TTS typically presented within one to two weeks after vaccination, primarily affecting women younger than 50 years old. General advice after vaccination included resting, drinking plenty of fluids, and contacting a healthcare provider if side effects were concerning or did not subside.