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The Capitol outbreak shows one vaccine dose may not fully shield against the coronavirus

Just because you got a Covid-19 vaccine doesn’t mean you’re invulnerable to reckless behavior.

House Speaker Nancy Pelosi receives a Covid-19 vaccination shot in her office on Capitol Hill in Washington, DC, on December 18, 2020.
Anna Moneymaker/AFP via Getty Images
Umair Irfan is a correspondent at Vox writing about climate change, Covid-19, and energy policy. Irfan is also a regular contributor to the radio program Science Friday. Prior to Vox, he was a reporter for ClimateWire at E&E News.

Can you still get Covid-19 after getting a vaccine? And can you still spread the virus that causes it to other people? As more Americans begin the process of vaccination, how much protection each dose provides in the real world is being put to the test.

At least three Democratic members of the House of Representatives recently found out the hard way. They were sheltering for hours with Republican colleagues who refused to wear masks during the Capitol riots on January 6 and later tested positive for SARS-CoV-2, the virus that causes Covid-19. Their experience suggests that one dose of a vaccine and masks may not be enough to protect someone in the face of hours of reckless behavior.

Rep. Bonnie Watson Coleman (D-NJ) reported on January 11 that she tested positive for SARS-CoV-2 and began experiencing symptoms, though she’d already received one dose of the Pfizer/BioNTech vaccine on December 29. Watson Coleman, who’s 75 and a cancer survivor, said she may have been exposed at the US Capitol during the riots as she sheltered with other representatives who refused to wear face masks.

“[S]he is always masked and that included the time she spent in the Capitol in lockdown,” said a spokesperson for Watson Coleman in an email.

Another Congress member who was in the same lockdown area on Wednesday with maskless colleagues, Rep. Pramila Jayapal (D-WA), announced Monday night she’d also tested positive. The Cut reports she received the vaccine on January 4.

On Tuesday, a third Democratic lawmaker, Rep. Brad Schneider of Illinois, who was also vaccinated on January 4, said he tested positive for the virus but was not experiencing any symptoms.

“Today, I am now in strict isolation, worried that I have risked my wife’s health and angry at the selfishness and arrogance of the anti-maskers who put their own contempt and disregard for decency ahead of the health and safety of their colleagues and our staff,” he added on Twitter.

The vaccines for Covid-19 that have been approved to date are highly effective, but the new cluster in Congress is a reminder that they’re not perfect, especially not at one dose.

Both the Moderna vaccine and the Pfizer/BioNTech vaccine are reported to be around 95 percent effective at preventing Covid-19 illness after two doses, but that means that a tiny fraction of people who were vaccinated could still get sick.

And since the two doses of both vaccines are supposed to be administered 28 and 21 days apart, respectively, it is possible for people to be infected between their shots as well. While the first dose of the vaccine does offer some protection, that protection takes days or weeks to build up, and it’s not as complete as the shield provided by two doses.

Testing positive for the virus does not necessarily mean that an individual will experience the disease and show symptoms. But it might mean that they can still transmit the virus to others.

The possibility of getting infected even after beginning an inoculation regimen was evident during clinical trials of Covid-19 vaccines.

In Pfizer and BioNTech’s application for an emergency use authorization from the Food and Drug Administration, they reported 178 Covid-19 cases among participants in their phase 3 clinical trial, with nine cases in the group that received the vaccine. The majority of those nine cases were between the first and second doses.

A graph comparing a placebo group to the treatment group in the Pfizer-BioNTech Covid-19 vaccine clinical trial.
Most Covid-19 cases in the Pfizer/BioNTech vaccine group (lower line in blue) occurred within two weeks of the first dose.

Moderna’s phase 3 trial showed a similar pattern, with 185 Covid-19 cases in the placebo group and 11 cases in the group that received the vaccine, most within two weeks of the first dose.

Chart comparing cases of Covid-19 in the placebo group and the treatment group in the phase 3 clinical trial of Moderna’s Covid-19 vaccine.
The Moderna Covid-19 vaccine trial also showed that people who received the vaccine can still get infected, but most infections were shortly after the first dose.

For both vaccines, it may also be the case that some of the people who reported Covid-19 symptoms were infected before they received their first vaccine dose. In rare cases, people may fall ill even after two doses, but the evidence points to a less severe course of the disease among the immunized.

It’s important to note (since there’s a lot of misinformation circulating on social media) that the vaccines themselves cannot cause infection. Both the Moderna vaccine and the Pfizer/BioNTech vaccine don’t contain any part of SARS-CoV-2. Instead, they use a strand of genetic material called mRNA that instructs the body to make a fragment of the virus.

There’s still more to learn about the protection offered by Covid-19 vaccines

One lingering concern about Covid-19 vaccines is that protection might not last forever. Since Covid-19 is still a fairly new disease and there’s only a few months of data on people who’ve received the vaccine, scientists are still trying to figure out how quickly immunity might wane. Based on experiences with past coronaviruses, scientists expect protection might last a few years, but that’s something that can only be verified with the passage of time.

Another important question is whether someone can spread Covid-19 to others after getting partially or fully vaccinated. Some early evidence from Moderna showed that its Covid-19 vaccine does block some transmission, but it might not be to the same degree that it prevents illness.

Determining this will take time, especially since many SARS-CoV-2 infections are asymptomatic and require testing to confirm. Researchers have reported recently that up to half of infections are caused by people who get infected but don’t show symptoms themselves, so it’s important to figure out how much asymptomatic transmission can still occur among the immunized.

If a vaccine does block transmission well, it means that it can provide a faster route to herd immunity. But since there are currently so many unknowns, people who have been vaccinated for Covid-19 should still follow all the regular Covid-19 precautions, like hand-washing, mask-wearing, and social distancing, especially when community transmission is as high as it is now. Vaccines are critical, but they are just one line of defense against Covid-19, and as the recent infections of members of Congress show, preventing transmission requires others to take precautions as well.