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Why Covid-19 Vaccines Can’t Be Silver Bullet: Immunity Explained

Nov. 19, 2020, 8:36 PM

Federal health officials are preparing to distribute, by the end of December, the first 40 million doses of Covid-19 vaccines from Moderna Inc. and Pfizer Inc./BioNTech SE, pending authorization from the Food and Drug Administration.

The 95% efficacy demonstrated by both vaccine candidates offers hope of ending the global spread of the novel respiratory disease.

But public health officials caution that the good news about vaccines doesn’t mean the shots will immediately stop the virus from spreading. It likely will take more than that to eradicate Covid-19. Here’s a reality check on what lies ahead:

1. Will I Still Have to Wear a Mask After Vaccination?

For a while, yes. While clinical trial data from Moderna and Pfizer/BioNTech SE shows that their vaccines protect people from Covid-19, it doesn’t rule out the possibility that someone could continue to spread the virus after they’ve been vaccinated—even if they are feeling well and show no symptoms.

2. What Will and Won’t the Vaccine Do?

The vaccine keeps people from getting sick. It doesn’t necessarily stop the virus from embedding itself into the lungs or other organs.

Both the Moderna and Pfizer vaccines are based on the genetic material that makes up the novel coronavirus. By exposing a person’s body to that material through a shot, the immune system can build the antibodies that fight the growth of the virus once it enters the respiratory tract.

That means a person who has received a full vaccine regimen—two shots based several weeks apart in the case of Pfizer and Moderna—could inhale the SARS-Cov-2 virus and not feel any symptoms. If that person does feel symptoms, they will be milder than if they hadn’t received the vaccine because the virus won’t have an unchecked ability to spread throughout the body.

It’s easier to trick the body into forming its own immunity against the virus once it enters the lungs or nasal passage. That keeps people out of the hospital and protects them against the most dangerous symptoms if they do inhale the SARS-Cov-2 virus.

3. How Does the Vaccine Play Into Herd Immunity?

It will take many months to reach “herd immunity"—the stage when a large portion of a community becomes immune to a disease, effectively stopping the spread. Once a vaccine is authorized, millions of doses will likely be rolled out in phases based on risk, with frontline health workers and the elderly going to the front of the line.

As more of the population becomes vaccinated, the danger from contracting what’s left of the virus decreases because people have the ability to fight it. When enough people have received the vaccine, some public health restrictions won’t be needed. A community’s increased ability to fight the virus will also slow its ability to grow inside the body, which diminishes the spread from person to person. Once a virus has nowhere to go, it’s effectively dead. But the process can take years.

Measles is a good example of how this works. In 1978, Centers for Disease Control and Prevention set a goal to eliminate measles from the U.S. within four years through vaccination. By 1981, the number of reported measles cases was 80% fewer compared with the previous year, but the disease wasn’t declared “eliminated” until 2000. And measles outbreaks have occurred in recent years when certain communities have forgone vaccinations.

4. How Long Before Things Return to Normal?

Definitely not immediately, although as the levels of vaccination grow over the first six months of 2021, some of the more stringent measures such as school closures might be relaxed.

Public health officials expect some restrictions to be in place for most of next year. Stores and other retail outlets may continue requiring masks and social distancing because it will be difficult to know which of their customers has received a vaccine. Restrictions on public gatherings will likely continue “until the level of virus is so low that the risk of someone getting infected is minuscule,” Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said at a Hastings Center event.

When new cases do appear, rapid contact tracing and isolation of exposed people will need to continue to stop a resurgence of the virus’s presence in a community.

To Learn More:

—From Bloomberg Law:
Covid Vaccine Freezers in Place for Rollout Once FDA Gives OK

Moderna, Pfizer Covid Trial Placebo Recipients Want Vaccine (2)

Universal Masks in U.S. Could Save 130,000 Lives Before Vaccine (1)

Tracking Covid Shot’s Safety Puts Strain on Health IT Networks

Free Covid Vaccine Called Good Path to Ease U.S. Restrictions (1)

The Virus Shot Goes in Your Arm, but Where Does Your Data Go?

—From Bloomberg News:
Moderna Vaccine Production Is Gearing Up, Partner Lonza Says (2)

Pfizer Plans Filing as Vaccine Proves 95% Effective

The Final Hurdle in the Covid-19 Vaccine Race Is Bureaucracy (2)

Vaccine Safety to Remain Unclear Until Millions Get Their Shots

To contact the reporter on this story: Jeannie Baumann in Washington at

To contact the editor responsible for this story: Fawn Johnson at