We’ll probably need booster shots for COVID-19. But when? And which ones? – The Denver Post

By Carl Zimmer, The New York Times

As the nation edges closer to President Joe Biden’s goal of a 70% vaccination rate, many people are beginning to wonder how long their protection will last.

For now, scientists are asking a lot of questions about COVID-19 booster shots, but they do not yet have many answers. The National Institutes of Health recently announced that it has begun a new clinical trial of people fully vaccinated — with any authorized vaccine — to see whether a booster of the Moderna shot will increase their antibodies and prolong protection against getting infected with the virus.

Although many scientists estimate that the Pfizer-BioNTech, Moderna and Johnson & Johnson vaccines authorized in the United States will last at least a year, no one knows for sure. It is also unclear whether emerging variants of the coronavirus will change our vaccination needs.

“We’re in uncharted waters here in terms of boosters,” said Dr. Edward Belongia, a physician and public health researcher at the Marshfield Clinic Research Institute in Marshfield, Wisconsin.

Why do we have to get a flu vaccine every year, but two measles shots during childhood can protect us for life?

Different pathogens affect our immune system in different ways. For some diseases, like the measles, getting sick once leads to lifelong protection from another infection. But for other pathogens, our immune defenses wane over time.

In some important respects, vaccines mimic natural infections — without requiring that we actually get sick. Measles vaccines can produce lifelong immunity. Tetanus vaccines, on the other hand, generate defenses that fade year after year. The Centers for Disease Control and Prevention recommends getting a tetanus booster once a decade.

And sometimes the virus itself can change, creating a need for a booster to produce a new, tailored defense. Influenza viruses are so mutable that they require a new vaccine every year.

How do COVID-19 vaccines stack up against others in terms of protection?

The short answer is that we cannot be sure yet, since people started getting vaccinated in large numbers only a few months ago.

“Even in the trials, we don’t know what the immune response is a year out,” said Dr. Kirsten Lyke, a vaccine expert at the University of Maryland School of Medicine and a leader of the NIH’s booster trial.

But early signs are encouraging. Researchers have been drawing blood from volunteers in vaccine trials and measuring their levels of antibodies and immune cells that target the coronavirus. The levels are dropping, but gradually. It is possible that with this slow rate of decline, vaccine protection will remain strong for a long time. People who were previously infected and then received the vaccine may enjoy even more durable protection.

“I think there’s a real possibility that the immunity could last for years against the original strain,” Belongia said.

If that possibility bears out, COVID-19 boosters might not be required for years. But that is a big if.

Will some COVID vaccines last longer than others?

Possibly. Scientists have already found that vaccines using different technologies can vary in their effectiveness. The strongest vaccines include Moderna and Pfizer-BioNTech, both of which are based on RNA molecules. Vaccines relying on inactivated viruses, such as those made by Sinopharm in China and Bharat Biotech in India, have proved somewhat less effective.