来自医学博士Daniel C. DeSimone的回答。
After getting a COVID-19 vaccine, it's still important to take safety precautions, such as avoiding close contact with others, to prevent the spread of the virus that causes coronavirus disease 2019 (COVID-19). Further research is needed to understand the immunity that a COVID-19 vaccine provides and how long protection lasts before experts will consider changing current safety recommendations.
After you get both doses of a COVID-19 vaccine, it takes about two weeks for your body to build up protection. But even then you could become infected with the virus that causes COVID-19. Keep in mind that the Pfizer-BioNTech COVID-19 vaccine is 95% effective in preventing the COVID-19 virus. The Moderna COVID-19 vaccine is 94.1% effective in preventing the COVID-19 virus. While your risk of getting the COVID-19 virus after being vaccinated is low, it is possible.
It's also not clear if the COVID-19 vaccines reduce the spread of the COVID-19 virus. As a result, it's not known if a person who is vaccinated could be a carrier of the COVID-19 virus and spread it to others, even if he or she doesn't become sick. More research is needed to determine if you are still contagious after being vaccinated.
Because of these factors, even once you're vaccinated you could still pose a health risk to unvaccinated family and friends by visiting with them in person. The risks of serious illness from COVID-19 are highest for people who are older. Nursing home residents are at high risk because they often have multiple underlying health problems, combined with advanced age.
Even after getting the COVID-19 vaccine, continue to follow safety precautions and consider avoiding in-person visits with friends and family until more is known about the immunity the vaccines provide. If you choose to have in-person visits, remember to keep distance between yourself and others (within about 6 feet, or 2 meters). Wear a mask. Visit outdoors, when possible, or open windows and doors to make sure the space is well-ventilated. And wash your hands often.