Many countries around the world initiated their covid vaccine rollouts earlier this year. While some countries, like Israel, the United Arab Emirates (UAE), and Bahrain, have managed to give significant portions of their populations the shots they need others, like the US and Canada, are still on the way to complete theirs.
Delays in vaccinations are partially the result of vaccine supply shortages, and partially the result of fragmented, underfunded healthcare systems lacking in federal support.
People who have received one shot may have to wait much longer than the recommended three or four weeks to get their second dose. Fortunately, these delays don’t necessarily spell disaster. “It’s really not a problem,” says David Topham, a microbiologist and immunologist at the University of Rochester in New York.
Like many other vaccines, the first two COVID-19 vaccines authorized by the Food and Drug Administration (FDA)—the Pfizer-BioNTech and Moderna vaccine—require two doses. The vaccine will be given three or four weeks apart, depending on the vaccine being used.
The timing of your second dose of the COVID-19 vaccine will be coordinated by the organization that provided your first dose. The two-week window to receive your second dose begins 21 days after the first dose for Pfizer-BioNTech and 28 days for Moderna. When the US Food and Drug Administration (FDA) granted these vaccines emergency use authorization, it did so prescribing those exact intervals for each, since that’s what they had data for.
The FDA has since acknowledged that spacing doses a little farther apart may not hurt. And on Jan. 21, the US Centres for Disease Control and Prevention said it’s okay to receive a second vaccine dose as many as four days early, or 42 days after the first dose. Neither agency has much data on what extra time between shots does to the vaccines’ effectiveness, but the CDC considers it a “permissible risk.” What is important is that both doses come from the same manufacturer.
Getting both doses of these vaccines maximizes your ability to receive full immunity from the vaccine. Receiving only one dose does not provide you with the full protection and does not give you the full effectiveness of the vaccine. First time immune cells encounter a potential threat, they need a few weeks to rev up their defensive engines and get their antibodies in gear. That’s why the first dose of the vaccine is called a priming dose: It’s like an immunological meet-and-greet. By the time of the second shot, the “boosting dose,” immune cells are already familiar with the general idea of the threat; they just need to fine-tune their antibody response to promote even stronger protection.
For the two-dose vaccines, receiving one dose does provide you with some protection, though we do not know the full extent of the protection or how long it might last. Receiving only one dose is not as useful as receiving the full second dose. Given the spread of the virus and the serious health risk it poses, the second dose is strongly recommended.
So in conclusion, if you’re contacted to schedule your second dose of a COVID-19 vaccine, please make every effort to receive it. It’s important to fully protect you and our communities.