You may be among the more than 170 million people who have taken at least one dose of a coronavirus vaccine, or you may still be waiting your turn. Regardless, there’s likely a crucial question on your mind: How long will the vaccines protect us against COVID-19?
The vaccines developed are highly effective at preventing disease in real-world conditions, and research suggests they should maintain their effectiveness over time. What remains unclear is exactly how long the vaccines confer immunity, if vaccines will need to be tweaked to fight emerging variants of the virus, and if booster shots may be needed later. Here’s everything we know so far.
When Does Immunity Kick In?
After receiving a vaccine, it takes weeks for your body to develop disease-fighting antibodies that make you immune, says Dr. Peter Gulick, an expert on infectious diseases at Michigan State University. Full protection occurs two weeks after the second dose of the Pfizer-BioNTech or Moderna vaccines, and two weeks after the one-and-done Johnson & Johnson vaccine.
The Centers for Disease Control and Prevention reported last week that, in a study of nearly 4,000 health-care workers, a single dose of the Pfizer and the Moderna vaccines were 80 percent effective at preventing infection and a second dose 90 percent effective. During a briefing Monday at the White House, Dr. Anthony Fauci pointed out that relying only on the first shot provides “tenuous” protection, with questions looming about the duration of the vaccine’s defense against the disease: “The question is how long does it last?”
How Long Does Protection Last?
The CDC’s official position is “We don’t know,” and Gulick told Intelligencer, “We’re just starting to understand how long that immunity may last.” A piece of the answer came last week from Pfizer, which announced that antibodies triggered by the jab and the strong immunity they prompt persists for at least six months among vaccinated individuals — even against more contagious variants. New research also suggests that the protection the Moderna vaccine gives lasts for at least six months. That doesn’t mean immunity from these shots stops at six months, it’s how long volunteers in clinical trials of the vaccines have been followed. Gulick says some experts “would say it may last even longer, but we don’t have a good answer as of yet.”
“The Moderna and Pfizer vaccines are shockingly good mimics of natural infection,” biologist and former Harvard professor William Haseltine told The Atlantic. “But it’s really important to stress the fact that these vaccines are likely to be temporary protection. A year or maybe two.”
Several factors may influence how much protection the vaccines provide and for how long, Chunhuei Chi, director of the Center for Global Health at Oregon State University, told the Washington Post. For instance, people who have a stronger immune response to a vaccine will produce more antibodies and memory cells — and therefore have stronger immunity, he said. But, he adds, there is not currently evidence to show that a stronger immune response will increase the duration of immunity. Another factor is whether new, more infectious variants crop up that could dampen the vaccine’s efficacy. “With my HIV patients with an immunocompromised system, I always warn them, ‘You got the vaccine, you’ll get immunity, but still be cautious and wear a face mask,’” Gulick said.
Will We Need Booster Shots?
Experts believe the coronavirus pandemic is likely to become endemic, meaning the virus will stick around in populations, potentially requiring booster shots to beef up immunity. “We need to plan that this is something we may need to maintain control over chronically,” Fauci said in November. “It may be something that becomes endemic, that we have to just be careful about.”
A good comparison for what COVID-19 will look like in the future is the flu, a disease that occasionally produces worrisome variants that cause outbreaks. Millions of people routinely get a flu shot each year, and those vaccinations are formulated to combat the latest mutations of the influenza virus. Currently, Pfizer and Moderna are studying whether a booster shot may be helpful in maintaining COVID-19 protection following initial vaccination, especially when it comes to variants like those first detected in the United Kingdom (B.1.1.7), South Africa (B.1.351), and Brazil (P.1). “The flexibility of our proprietary mRNA vaccine platform allows us to technically develop booster vaccines within weeks, if needed,” Ugur Sahin, CEO and co-founder of BioNTech, Pfizer’s partner in vaccine development, said in a press release. Johnson & Johnson is also testing its own booster.
Gulick believes there will be a need to develop a test in order to measure people’s antibodies. “In theory, we could monitor and say, ‘Okay, your levels of antibodies are declining now. We need a booster or another vaccine,’ or ‘Yours are good,’” he says. Experts are working on this testing, but, he says, “because we don’t have that right now, everything is kind of speculative.”