![The CDC considers a person to be fully vaccinated two weeks after the final dose of the COVID-19 vaccine. [Evgenia Parajanian / Shutterstock]](https://npr.brightspotcdn.com/dims4/default/7dc1cd7/2147483647/strip/true/crop/3000x2003+0+0/resize/840x560!/format/webp/quality/90/?url=http%3A%2F%2Fnpr-brightspot.s3.amazonaws.com%2Flegacy%2Fuploads%2F2021%2F4%2F12%2Ffully%20vaccinated.jpg)
What are your questions about the coronavirus vaccine?
ideastream's health team is answering as many questions as possible, with help from local experts in a range of fields. You can send us your questions with our online form, through our social media group, or call us at 216-916-6476. We'll keep the answers coming on our website and on the air.
Marcelo writes to tell us he tested positive for COVID-19 three days after receiving the single-dose Johnson and Johnson shot, and he wonders if he needs to get another dose of the vaccine.
Another dose isn’t necessary, according to Dr. Keith Armitage, an infectious disease specialist at University Hospitals.
It’s possible Marcelo got infected with COVID-19 after he got the shot, but before he was fully vaccinated, Armitage said.
“People can get infected up until day 12, and then people can test positive for a long time,” he said.
For the Johnson and Johnson vaccine, Armitage said protection starts about two weeks after receiving the shot, but is much better after 28 days. So Marcelo wasn’t fully vaccinated when he tested positive.
Armitage said data presented to the FDA show that a patient’s antibody levels increase for 56 days after receiving the Johnson & Johnson shot. That means a person will continue to gain more protection over time.
People who receive Pfizer or Moderna vaccines are fully vaccinated two weeks after receiving the second dose, according to the CDC.
Marcelo could have gotten infected before or after the shot, Armitage said. Tests can detect COVID-19 weeks after a person first becomes infected, and a person can test positive without having any symptoms.
This is why it's important to continue to wear a mask and practice social distancing even after you receive the vaccine, he said.
It's also important to note that none of the vaccines are 100 percent effective, so it’s still possible for someone to become infected after receiving the vaccine. But health experts agree that the vaccines significantly decrease a person’s risk of becoming severely ill if they do get sick from COVID-19.
