CNN  — 

Covid-19 vaccines are very effective against preventing infection, but no vaccine is 100% effective. Fully vaccinated people can and do become infected. It’s not known exactly how many of these breakthrough infections are occurring, as the US Centers for Disease Control and Prevention is not collecting national data this comprehensive. Based on reports from 25 states that do keep track of these data, the Kaiser Family Foundation estimates that the rate of breakthrough infections is well below 1%.

Many people have questions about what to do if they are vaccinated but test positive. Should they isolate, and for how long? What about family members — should they all get tested? What kinds of symptoms should make someone concerned that they might have a breakthrough infection? And how to address skeptics who question getting the vaccine if you can still get the coronavirus?

To glean answers to these questions, we turned to CNN Medical Analyst Dr. Leana Wen. Wen is an emergency physician and visiting professor of health policy and management at the George Washington University Milken Institute School of Public Health. She’s also author of a new book, “Lifelines: A Doctor’s Journey in the Fight for Public Health.”

CNN: What should people do if they get a breakthrough infection? Should they isolate from their household members? Does it matter if they have symptoms?

Dr. Leana Wen: Someone who’s vaccinated and tests positive for Covid-19 should definitely follow strict isolation protocols because we have to assume that the person is contagious and able to infect others. If that person is symptomatic, they should isolate for at least 10 days counting from the first day they started having symptoms, according to the CDC. They can end the isolation as long as they haven’t had a fever for more than 24 hours and other symptoms are improving. If the person is not symptomatic but still had a positive test, they should stay isolated for 10 days following their positive test.

Isolation means that they should not be going in public where they could infect others. They should also isolate from close household contacts. That means, if possible, staying in a part of the house away from others, in their own room. Essentially, once a person is infected with Covid-19, it doesn’t matter for the purpose of isolation whether they were vaccinated — they could be contagious to others and need to follow standard isolation procedures.

CNN: If one person in the household gets a breakthrough infection, should everyone get tested?

Wen: Yes. Close contacts should all be tested, with “close contact” defined as being within 6 feet for a total of at least 15 minutes over a 24-hour period during the potentially contagious period. The CDC differentiates guidance for those who are vaccinated versus those who are not. Those unvaccinated, if exposed to a close contact who has Covid-19, should quarantine for 10 days. They can shorten the quarantine to seven days if they have a negative test at least five days after exposure. During that quarantine period, they cannot be in public.

On the other hand, those fully vaccinated, when exposed to a close contact who has Covid-19, do not need to quarantine unless they develop symptoms. They should still get tested within three to five days after exposure and wear a mask in public for extra protection.

CNN: Does that mean a vaccinated person with a Covid-19 exposure can still go to work?

Wen: According to the CDC guidance, yes, as long as that person doesn’t have symptoms, and they keep a mask on at all times and still get tested three to five days after exposure.

CNN Medical Analyst Dr. Leana Wen  explains what to do if you're vaccinated but test positive. A woman receives a rapid Covid-19 test in Hanover, Germany.

This CDC guidance is missing needed nuance. Consider this: Would you be comfortable sitting shoulder to shoulder with a work colleague around a conference table if you knew that this person’s spouse was just diagnosed with Covid-19? Even if the CDC guidance says that this can be done, I think we need to use some common sense, too. If your spouse or child has Covid-19 and you’re still waiting for your coronavirus test, I’d urge you to tell your supervisor and see if you could work from home at least until you get a negative test result.

I’d also distinguish between what was the level of your exposure to the person who tested positive. If you were at an outdoor party and standing next to someone who ended up testing positive, you should still get tested yourself, but your risk of having coronavirus is pretty low, and it might be reasonable to continue going to work — masked, of course. But if it’s your child or partner with whom you spend many hours together, in close, indoor quarters, you are at much higher risk of contracting Covid-19 from them and so should try not to expose others if possible.

CNN: What are the symptoms of breakthrough Covid-19 infections?

Wen: The key benefit of vaccination is that it reduces the likelihood of severe illness. Those vaccinated who still contract coronavirus are much more likely to have mild symptoms compared to if they were not vaccinated. An individual who might have been very ill with high fever, severe cough and so much trouble breathing that they need oxygen or a ventilator, could now instead have body aches, fatigue and the sniffles. That’s the power of vaccination — it reduces the severity of illness.

Since the symptoms in the vaccinated are much milder than the unvaccinated, be on the lookout for even one of the symptoms of Covid-19. These include fever, chills, cough, fatigue, muscle or body aches, headache, sore throat, runny nose, nausea, diarrhea and loss of taste or smell. Of course, this is a broad list, and it could indicate other viral illnesses, too.

Given how much coronavirus is surging in most parts of the country, keep your radar on high alert. If something doesn’t feel quite right to you, get tested.

CNN: If you find out you’re positive, should you tell your colleagues? What if you were at a party — do you tell the host?

Wen: You should follow procedures at your workplace. Talk to your manager, who may direct you to your company’s human resources department or someone else who can help with contact tracing. Generally, this would include identifying the individuals with whom you had close contact in the time period that you could have been contagious. This typically includes up to 48 hours before the beginning of your symptoms.

You should definitely think through what social activities you were engaged in during that potentially infectious period. If you were at a party, you should tell the host, as well as guests with whom you can remember spending prolonged periods of time with.

This is work that your local health department’s contact tracers should be conducting, but in many places, they are overwhelmed. Remember, too, that the contact tracers depend on you to recall where you were, and you would know best as to who you were with when. It’s important to let those you could have exposed know as soon as possible; we would want the same courtesy ourselves.

CNN: Do you need to test again before you’re cleared to go back to work?

Wen: No. Assuming you haven’t had a fever for more than 24 hours and your other symptoms are improving, 10 days after the beginning of your symptoms is the isolation period as recommended by the CDC. After that, you can end isolation and go back to work and interact with others.

CNN: Would a booster shot help to reduce breakthrough infections?

Wen: Probably. Federal health officials have already said that people who are moderately or severely immunocompromised, who received the Pfizer or Moderna vaccines, can receive a third dose now. The White House just announced that beginning the week of September 20, pending a final go-ahead from the FDA and CDC, they will begin allowing people who are at least eight months from their initial vaccinations to get a booster dose. That’s because vaccine effectiveness against symptomatic illness appears to decrease over time (though the vaccines still protect very well against severe disease), so one might expect that a booster shot would prevent future breakthrough infections. I’d advise that you speak with your doctor. The decision for a booster dose is probably not a one-size-fits-all recommendation, but an individualized decision depending on your medical circumstances.

CNN: Some people might be asking what’s the point of getting vaccinated if breakthrough infections can still happen?

Wen: We get vaccinated for two reasons. Remember that vaccination reduces the likelihood of severe illness — according to estimates from CDC data, by about 25 times. Second, vaccination also reduces getting Covid-19 by about eight times. A vaccinated person is much less likely to get sick from Covid-19 and spread it, compared to someone who is not vaccinated.

Get CNN Health's weekly newsletter

Sign up here to get The Results Are In with Dr. Sanjay Gupta every Tuesday from the CNN Health team.

Why do breakthrough infections still happen? We can think of vaccination as a very good raincoat. The raincoat will keep you dry in a drizzle. It might even work in a thunderstorm. But if you are in thunderstorms day after day, and sometimes going through hurricanes, at some point, you may get wet. The problem isn’t that the raincoat isn’t working — it’s that there is too much bad weather all around you.

That’s what is happening now with Covid-19 around the country. The level of virus is so high that the vaccine alone may not be enough to protect you. That’s why a mask can help, as can reducing the number of high-risk environments you’re in. Ultimately, we need to reduce the level of virus around us — and the best way to do that is through all of us getting vaccinated.