Despite the messy rollout so far, the arrival of the COVID-19 vaccine is a beacon of hope for many New Yorkers who want to safely return to some semblance of normal human interaction—a Super Bowl party, perhaps—in the not-too-distant future. But new questions are coming up about safe and appropriate social behavior now that some people are immunized against the virus while others remain ineligible, unable, or unwilling to get the vaccine.

Dr. Stephen Morse, a professor of epidemiology at Columbia University, answered some of our questions about how to act after you or your loved ones get vaccinated. The responses were lightly edited for clarity.

How long does it take the immune response to build defenses after vaccination?

[Being fully vaccinated] means getting two shots at the appropriate time and then waiting two weeks after the second one to make sure the immune response has really started to kick in effectively.

Should vaccinated people continue to wear a mask and social distance?

Absolutely. In fact, with these new variants that you’ve heard about that appear to be more transmissible, it is even more important to keep up what we call non-pharmaceutical interventions—the masks, social distancing, hand hygiene, trying not to [socialize] indoors or at least trying to have ventilation, and trying to avoid crowds.

Not everyone has had the vaccine yet. We know these vaccines do a very effective job at preventing clinical illness, but we don’t know if the vaccine will prevent someone who’s immunized from developing an asymptomatic infection and passing it on to others. We also don’t know how long immunity is going to last. It seems to be suitable at least for a few months after the second dose for the Pfizer and Moderna vaccines. This duration is similar to others that are now being tested, but it will take time to find out exactly how long that protection will last.

Can a group of people who are all vaccinated hang out normally?

It is less risky in that they all at least are not likely to get sick or make each other sick. One concern right now is that we would like to suppress transmission of the virus. The more it’s transmitted, the more opportunity there is for all these variants to evolve to be more transmissible.

People can perhaps relax somewhat. We can somewhat enlarge our group hangouts, and families can get together more if everyone is vaccinated. But until we know for sure whether the vaccine also prevents transmission, there is that possibility that someone can get infected and pass it on to someone who’s unvaccinated.

Can I visit my elderly parents in their apartment if they’re vaccinated and I’m not?

You could safely visit them. At least from your parents’ point of view, you’re not going to represent a danger to them, from what we know.

Now that the higher-risk people are getting vaccinated, if they get the two shots and wait a couple of weeks, there’s a better than 95% chance they’re not going to get sick even if they become infected. Younger people can still get infected, and some can also get unexpectedly sick. We can’t throw all precautions to the wind, but we can feel a lot more relaxed about visiting parents, other elderly relatives or people who have some underlying medical condition. They can feel better about it, too.

Would you still recommend wearing a mask and social distancing in that situation?

I think that becomes more of a personal choice. I know a lot of people find that in family settings, it’s hard to do that. It depends on how risk-averse you and your parents are. But you will still need masks at other times and so will they.

Is it recommended to keep getting tested for COVID-19 after getting vaccinated?

As far as I know, there’s no official recommendation on that. For those being immunized, the big question is, Can they still get infected? So some organized effort to test the fully vaccinated and collect the data would be particularly helpful.

[Ed note: The vaccine itself will not cause someone to test positive for a current COVID-19 infection, according to the Centers for Disease Control and Prevention.]

When will we know more about whether the vaccine protects against infection?

It’s mostly a matter of resources and finding the right sample of people to study. You want to find people who have been immunized and have some reasonable probability of knowing they’ve been exposed [to the virus]. Health care workers might be one way to target that. But vaccine companies and governments probably are researching it now or planning to do so. Countries that are well organized like Israel are in a much better position to answer some of these questions because they can get ready access to people after they’ve been immunized to test them. So, we should also be looking internationally.

When will it be safe to socialize normally again?

Once we reach a sufficiently high level of herd immunity. What herd immunity means is the infection just can’t find new people to infect very easily. That’s closely related to how transmissible the virus is. That’s why we’re worried about more transmissible variants. It’s not only easier to catch them, but to control them with immunization and other measures. You need a higher level of herd immunity.

For [COVID-19], we think it’s about 80%. It’s going to take a while to get that many people immunized. Even as we’re getting to that point, we’ll still need to keep up those same precautions but we’ll see less and less transmission, we hope, as there are pockets of herd immunity. Hopefully New York City will eventually be one, but we’ll see.

But you will also see that our flu season here was much milder than usual. The social distancing, the avoidance of mass gatherings, hand hygiene and so on were all recommendations made years ago for pandemic influenza. I don’t know if we’re going to make a habit of keeping this up.

Even if we keep it up imperfectly, it’s going to reduce our illness and death from the flu and from some other respiratory infections. So, there are reasons not to completely throw away all the masks after we’ve been immunized.