The two-shot coronavirus vaccines have been shown to have considerable efficacy rates even after a single dose, but there’s still a chance you can contract COVID-19 after receiving your first shot. This is why the time between shots (and immediately after) is so important: That is when your immune system is learning how to protect you properly — and unfortunately, you're not completely in the clear.
“Especially between the two doses of a two-dose vaccine like Pfizer or Moderna, it’s important to make sure that you still take precautions because you’re not fully vaccinated and you could get infected in-between those two doses,” Amesh Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security, told Refinery29.
The reason for this has to do with the effectiveness of a single dose in a two-dose system. The Pfizer-BioNTech vaccine is only 52% effective after the first shot, according to one study. While the Moderna vaccine shows 80% effectiveness after the initial dose, both of these vaccines start working at their optimal levels about two weeks after the second dose, when their efficacy rates jump to over 90%. According to the Centers for Disease Control and Prevention, it takes about 14 days for your immune system to fully respond to the coronavirus vaccine. That’s why the second shot is so important.
It also seems to matter at what point during your vaccination schedule you get infected. “If you got COVID between doses of the vaccine, when you got it in that interval would likely influence how severe the symptoms might be,” Adalja explained. “If it was two weeks post your first dose, I suspect that the vaccine-induced immunity would have some impact on how bad the infection might be. So it’s likely to be a little bit less severe if it’s two weeks or more past the first dose. And I think if it’s before that, you probably don’t have much vaccine-induced immunity. Maybe some after a week, but it could be more like a normal case of COVID-19 that you would have had were it not for the vaccine.”
So what should you do if you get sick in-between shots? The advice will sound familiar, as it is pretty much the exact same thing you’d do if you got the virus without a vaccine. First things first: Isolating yourself will keep you from spreading the virus to others. And, you should still go for shot #2. “You should get your second dose as planned,” Adalja said. “But only if you’re not still contagious. So it should be 10 days or so since you developed symptoms or tested positive before you get your second dose so you don’t expose anybody when you’re getting vaccinated.” However, it is important to note that this time frame may vary for people. Abisola Olulade, MD, a physician in San Diego, told Refinery29 that someone who is immunocompromised may take longer to recover fully before being able to safely receive the second dose. “Possibly for up to 20 days, and you should discuss this with your doctor,” she added.
Once you’ve recovered and are symptom-free with the all-clear from a medical professional, you are able to receive the second dose of the vaccine as planned. There’s no evidence that having COVID would impact the effectiveness of the second dose, Dr. Adalja said. If this all takes place before your original booster appointment, then stick to your original appointment time as long as you get the go-ahead from your doctor. But if the three or four weeks between doses have passed, you should try to reschedule your appointment as soon as possible.
Currently, there is limited data on what happens if you wait too long between vaccine appointments. “The CDC has stated that you can wait up to six weeks before getting a second dose of the mRNA vaccines,” said Dr. Olulade. “Beyond this time frame, there is limited data available on efficacy. We don’t have a lot of evidence on how it would affect the efficacy at this point.”
It’s important to remember that even at full efficacy, no vaccine currently on the market completely prevents you from getting coronavirus. Even after you get the second dose, you could still become infected. What the vaccine does do, though, is make that possibility rare, and most importantly, it keeps symptoms from becoming severe. In fact, studies have shown that your risk of contracting a serious case after being vaccinated is incredibly low.
"Two weeks after [your] second dose of the Pfizer or Moderna vaccine, I do think you can become much more open about the activities that you engage in because you are definitely protected from severe disease, symptomatic disease, and highly unlikely to be a transmitter of the virus," Dr. Adalja said.