FEW ANSWERS ON VACCINE’S LENGTH OF PROTECTION

You may be among the nearly 100 million people in the United States who have taken a coronavirus vaccine. Or you may still be awaiting your turn. Regardless, there’s a crucial question on most of our minds: How long will the vaccine really protect us?

As with most aspects of the virus, the answer is not completely clear. Why? Because although Americans have been battling the pandemic for more than a year, the vaccines were granted emergency use authorization relatively recently, so experts have not had time to observe their long-term effectiveness.

That research is underway, and in the meantime, experts say we can make an educated guess.

1. How long will vaccine-supported inoculation last?

Federal health authorities have not provided a definitive answer, but based on clinical trials, experts know that vaccine-induced immunity should last a minimum of about three months. That does not mean protective immunity will expire after 90 days; that was simply the time frame participants were studied in the initial Pfizer, Moderna and Johnson & Johnson trials. As researchers continue to study the vaccines, that shelf life is expected to grow.

In the real world, immunity from the vaccines should last quite a bit longer, experts say.

2. What factors influence immunity?

Chunhuei Chi, director of the Center for Global Health at Oregon State University, said immune responses vary from person to person. People who have a stronger immune response to a vaccine will produce more antibodies and memory cells and therefore will have stronger protection, he said. But there is no evidence to show that a stronger immune response will increase the duration of immunity.

And it does not mean people with a stronger immune response will have more severe side effects from the shots or vice versa, according to a recent survey by the British National Health System.

Immunity also could depend on what happens with future variants. If a person were exposed to a variant capable of evading vaccine-induced antibodies, a vaccine might not be as effective as initially expected, said Lana Dbeibo, an infectious-disease expert at the Indiana University medical school.

3. Can we extrapolate from what we know about natural immunity?

Yes.

In fact, much of this hypothesizing comes from extrapolating data examining immune responses in people who have had COVID-19 and illnesses from other coronaviruses, rather than in people who have been vaccinated, said Dbeibo, director of vaccine initiatives for Indiana University.“But vaccine responses should not be less reliable than in natural infection,” she added.

Research shows that people who have been infected with the coronavirus retained immunity that was robust after eight months. That gives researchers a starting point in predicting how long immunity may last after vaccination, Dbeibo explained.

But antibodies will wane. And though it is a gradual process, once antibodies decline to a level that is no longer protective, reinfection is possible. Still, the infection probably will be milder, experts say.

Experts also are speculating whether immunity to SARS-CoV-2 will be as durable as with seasonal coronaviruses, which people contract repeatedly. Experts estimate that immunity from those viruses lasts a couple of years.

4. What now?

Experts are still trying to determine how long it will take for antibodies to decrease to the point where they are no longer protective. But once that happens, people will need boosters to remind their immune systems to make more antibodies against the disease. Evidence suggests that the available vaccines are still effective against most variants.