Three questions and the emerging answers about COVID-19 Vaccine protection--NPR

As the COVID-19 vaccine rolls out, three big questions loom. First, can someone who has been vaccinated still spread the disease? Second, will the vaccine remain effective as the virus itself evolves? And third, how long will the vaccine's protection last?

Answers to these questions lie in our immune systems. And the answers aren't straightforward because our immune systems are both remarkably adept and remarkably challenging to predict.

...the first question, about whether people who are vaccinated can still spread the disease. Marion Pepper, an immunologist at the University of Washington, says that's not just an open question for this vaccine, but for vaccines in general.

"I think it's hard to say because we're constantly being bombarded by different pathogens and we don't know when your immune system is responding," she says. We may have infections that don't make us sick, so we never know about them. But we could be spreading disease.

When a person is infected – or inoculated with a vaccine – the immune system gears up to produce antibodies that specifically target the virus. Over time, those antibodies naturally wane. But the immune system still holds a memory of the virus, and if it ever shows up again, cells spring into action and start to gear up a new batch of antibodies. However, that process can take three to five days. ...

The second question, about whether the vaccine will remain effective even as the virus evolves, is harder to answer. Scientists thus far aren't too concerned about the current strains of the virus that are spreading globally – vaccines will apparently still work against them. But the virus will continue to morph, with uncertain consequences.

"Even though everyone is obviously concerned about a virus evolving, your memory B cell responsiveness also evolves over time," Pepper says. ...

Finally, is the question of how long a vaccine will last.

In some instances, your immune system can have a very long memory.

"Some natural infections can give you lifelong immunity," Jameson says. "You only get it once and you're protected for the rest of your life."

Vaccines mimic a natural infection to trigger an immune response. But vaccines may require a boost to keep that immunity strong. The memory B cells that target the coronavirus that causes COVID-19 may not have the staying power of the cells that protect us from the measles, for instance. So far, scientists have observed that these memory B cells have persisted for many months following a case of COVID-19, but it's too early to say anything about whether they will eventually fade. ..