Your next-wave Covid-19 vaccine questions, answered by an expert

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Regulatory authorities across the globe have authorized several Covid-19 vaccines for emergency use. Now the challenge is getting those shots into arms. And while much of that challenge is logistical, there’s a communication hurdle, too.

Even people who trust scientists and the vaccine development processes have questions about what to expect. So on March 3 Quartz sat down with Panagis Galiatsatos, a pulmonologist and critical care specialist at the Johns Hopkins Bayview Medical Center, to answer our readers’ latest questions about the rollout of vaccines. You can watch the conversation above, and read answers to some of the key questions below.

When will we know if vaccinated people can transmit the virus?

Unfortunately, this isn’t something we can establish by recruiting participants into a clinical trial, as scientists did when testing the safety and efficacy of vaccines. “The way we’re going to prove this is through observational trials,” Galiatsatos says.

We do have reason to believe that fully vaccinated people mingling together won’t be able to get one another sick, and it’s also reasonable to expect that once enough people in a group have been vaccinated, herd immunity can be achieved—meaning even unvaccinated people won’t pick up the virus. That comes from the virus not having anywhere to live; if too many people around have immunity and can’t host it, it will eventually die out. Estimates project herd immunity will be reached when 60% to 90% of the population is vaccinated.

Are there more risks associated with Covid-19 vaccines than other vaccines because of how quickly they came out?

These vaccines were developed quickly—and that’s a great thing, Galiatsatos says. “We just saw the pace of science” without man-made barriers, like the cost of running clinical trials that may fail. In many cases, the US government ate those costs so pharmaceutical companies could get trials up and running faster.

But there are still many independent regulatory bodies looking at the data from companies’ clinical trials, and the parameters these groups used to justify authorizing these vaccines for the public didn’t change from pre-Covid times.

There are questions the clinical trials haven’t answered, like how long immunity from vaccines can last, and whether vaccinated people can transmit the virus to others. These data are still being gathered through ongoing observational studies of participants who were in original phase 3 trials.

How can we assess the long-term effects of these vaccines?

Because Covid-19 vaccines haven’t been around for a long time, “we’re going to have to extrapolate,” says Galiatsatos. However, scientists have reasons to believe that there likely won’t be long-term effects, based on the lack of significant long-term effects from other vaccines, like the annual flu shot.

Additionally, some participants in vaccines’ stage 3 clinical trials are still still being monitored, and will be for more than two years after they finish the vaccination course. In the US, there’s also a system for reporting adverse events after Covid-19 vaccines so doctors can keep an eye out for any unexpected symptoms.

Have we learned anything else about the side effects of Covid-19 vaccines?

By and large, side effects from the Covid-19 vaccines have remained relatively stable: Some people have mild pain at the injection site, and may feel achey or feverish for a couple of days. Most people feel those side effects slightly more after the second dose, in the case of Pfizer and Moderna’s vaccines. These side effects are merely an indicator that your immune system is gearing up a response—although you don’t have to feel them to enjoy the immunological benefits of a vaccine.

Galiatsatos compared this brief discomfort to going to the gym: We don’t always feel great at the end of a long, hard workout, but those feelings of being out of breath and sweaty dissipate over time. And in the long run, our bodies benefit from the exercise.

Anaphylaxis can happen to some people with certain allergies. But having an anaphylactic reaction to something in the past doesn’t preclude someone from getting a vaccine altogether. Instead, healthcare providers may want to observe that person for up to a half hour after getting the vaccine to make sure they’re safe.

Is there an optimal length of time to wait in between first and second doses? What if I get my shot outside of that window?

Spacing for vaccine doses isn’t an exact science; the three and four weeks in between vaccinations for the Pfizer-BioNTech and Moderna doses, respectively, come from the fact that those were the timelines that were studied in clinical trials. Earlier this year, the US Centers for Disease Control and Prevention gave guidance for a little more wiggle room around dose-timing, saying it was permissible to receive a second shot four days early, or up to six weeks after the first dose.

If that isn’t possible, “you want to get it in a window of 90 days,” Galiatsatos says. Although this timeline hasn’t been studied yet either, he’s recommending it based on what we know about immunology; any longer, and he fears that the immunity from the first dose may wane.

Getting the shots too soon probably won’t elicit any worse of an immune response, he says, but it may leave a person open to experiencing more of those uncomfortable, temporary side effects.

Can I mix vaccine types if I want to get a second dose faster?

At the moment, there’s no data on mixing vaccine types and doses—so it’s probably not likely that you’d want to mix doses when accruing your initial immunity. But Galiatsatos says it’s highly likely that, should we need to get SARS-CoV-2 vaccine booster shots like we do for the annual flu, it won’t matter which manufacturer it came from.

Do we have any more data if pregnant people should be given the vaccine?

At the moment, there’s no great data on whether pregnant people should get the vaccine, but observational studies are ongoing. The American College of Obstetricians and Gynecologists has pushed for pregnant people to be allowed to receive the vaccine, should they want it, because it doesn’t seem to be dangerous so far.

Galiatsatos says that there are two main things he as a health care provider is looking out for: any adverse events reported in pregnant individuals who elect to get the vaccine (so far, there haven’t been any), and mouse model data as a proxy for human studies. “We constantly test pregnant mice to see if they’re okay…and the mouse models were perfect.”