Letters to the Editor • Opinion
We already know how to prevent pandemics
(Joel Saget/AFP via Getty Images)

Michael S. Saag is associate dean for global health and the director of the Center for AIDS Research at the University of Alabama at Birmingham.

It will take at least 10 months — and perhaps longer — after a vaccine is approved for use for one to be administered to a sufficiently large number of people across the country to bend the curve of new covid-19 cases. At least 60 to 70 percent of the population needs to be immunized in order to reduce the number of people susceptible to the infection so that the pandemic can no longer sustain itself.

In the meantime, it is critical for all of us to fully commit to using public health measures (masks, distancing, avoiding crowds, hand hygiene) to buy time until that day arrives.

And we need to keep one other thing in mind: The immune system’s success in fighting infections is rooted in memory. Strange as it seems, our bodies need time to learn how to fight this disease.

Think of the immune system as the body’s Defense Department. Its army consists of millions of infantry-like cells that storm the invaders, causing local redness and pus at the site of battle. Its navy uses radar-like receptors to scope out the enemy and send signals — in the form of chemokines — back to headquarters to help direct and coordinate the attack. The air force drops smart bombs, or antibodies, on the invaders to block their attack.

Full coverage of the coronavirus pandemic

But covid-19 is a bug that our bodies have never seen or fought before. And this virus is particularly evil — I know because I have both had it myself and spent the past six months assisting with the University of Alabama’s response to it. Covid-19 manipulates the immune response in such a way that the normal command-and-control signals that tell the immune system to "stand down" after it has attacked the invader are commandeered, or hijacked, by the virus. A dysregulated, out-of-control immune system turns on the host body itself, creating collateral damage in the tissues, resulting in worsening illness and, in too many cases, death.

Humans have been trying to understand immunity since the plague of Athens in 430 BC. But over the past several decades our understanding of how the immune system works has become much more sophisticated. We know now that our immune system works best when it has fought a disease before and, in the process, literally develops the memory of how it won the fight. When our immune system encounters new threats, it takes time to learn how to fight back.

Which brings us to the vaccines under development by Pfizer and Moderna. The intent of all vaccines is to mimic a real infection, allowing the immune system to develop a response that establishes “memory” should the host later become exposed to the actual infection. With covid, it is especially important to prevent infection before the virus has the opportunity to create severe immune dysfunction.

The Pfizer and Moderna covid-19 vaccines would inject the genetic code of a part of SARS-CoV-2 into a person’s muscle tissue. That code uses the muscle cells as a factory to produce the covid-19 protein at the site of injection. The vaccine functions as a spy of sorts, showing the body’s immune-system cells what the protein looks like so they’ll be prepared to fight should the vaccinated person ever encounter the virus.

Many investigators, including me, were skeptical that the resulting immunity generated by these vaccines would actually prevent infection. Over the past several decades, after all, we had seen similar types of vaccine-induced immune responses to HIV and other pathogens, only to discover that the candidate vaccines failed to protect against acquisition of infection for a variety of reasons. In short, many candidate vaccines may create “memory” from the exposure, but they fail to keep you from becoming infected. Hence the need for additional studies to prove protection.

Over the past 10 days, both Pfizer and Moderna announced that their mRNA vaccines were spectacularly protective. In each study, among the first some-95 subjects who developed covid-19, the vast majority (90 to 95 percent) of infections occurred in those who received placebo; only a few vaccine recipients became infected. Most scientists hoped for 70 percent efficacy; the 90 percent result was beyond our wildest expectations.

While the general public will focus on the overall success rate, scientists will focus intensively on the handful of participants who developed covid-19 after receiving the actual vaccine.

What is different about their immune response compared to others who were protected by the vaccine? Is there a gap in their immunity? Conversely, among those vaccine recipients with successful protection, which immune-system responses are most important in protecting against infection? Is it the antibody response? The cellular immune response? We still have much to learn.

Knowledge of these correlates of immunity will be used, among many things, to determine how long the effects of the vaccine will last, indicating when a booster vaccination might be administered. All that takes time.

The immune system’s success in fighting infections is rooted in memory — which is ironic since so many of us seem to have forgotten how to fight this disease in our daily lives. A question for us: Have we been hijacked by the virus as well?

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Distrust in the Trump administration has turned into distrust of science, adding to an already powerful anti-vaccine movement. (Video: The Washington Post, Photo: Joseph Prezioso/AFP-Getty/The Washington Post)

Read more:

Leana S. Wen: We should be just as careful about covid-19 in relatives’ homes as we are in grocery stores

Megan McArdle: My No. 1 Thanksgiving tip: Don’t gather this year

Leana S. Wen: Stop talking about a ‘national lockdown.' It won’t happen, and it is a distraction.

The Post’s View: The coronavirus’s origins are still a mystery. We need a full investigation.

The Post’s View: The pandemic is galloping ahead. The president is AWOL.

Coronavirus: What you need to know

Where do things stand? See the latest covid numbers in the U.S. and across the world. In the U.S., pandemic trends have shifted and now White people are more likely to die from covid than Black people.

The state of public health: Conservative and libertarian forces have defanged much of the nation’s public health system through legislation and litigation as the world staggers into the fourth year of covid.

Grief and the pandemic: A Washington Post reporter covered the coronavirus — and then endured the death of her mother from covid-19. She offers a window into grief and resilience.

Would we shut down again? What will the United States do the next time a deadly virus comes knocking on the door?

Vaccines: The CDC recommends that everyone age 5 and older get an updated covid booster shot. New federal data shows adults who received the updated shots cut their risk of being hospitalized with covid-19 by 50 percent. Here’s guidance on when you should get the omicron booster and how vaccine efficacy could be affected by your prior infections.

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