As more Americans get vaccinated, our knowledge of COVID-19 and the efficacy of the vaccines grows. While all three currently available vaccines have been proven effective at preventing moderate to severe COVID-19 illness, recent research shows there is still the remote chance that people can contract the disease after vaccination.
However, according to the Centers for Disease Control and Prevention (CDC), if post-vaccination infection does occur, it will likely lead only to very mild illness or possibly infection without symptoms, known as asymptomatic infection.
Vaccination is vital, even if infection is possible
COVID-19 vaccination works by priming the immune system to first recognize the novel coronavirus that causes COVID-19 and then spring into action to protect from illness. Even though many people with COVID-19 experience mild symptoms, some people become severely ill, require hospitalization, have long-term health effects or even die. There is no way to know how your body will react to the virus. So vaccination is vital.
But it is important to be aware that infection after vaccination is possible. Here’s why:
Enough time needs to pass after vaccination to develop immunity. Even after receiving the vaccine shots — 1 dose for the Johnson & Johnson vaccine, and 2 doses for both the Pfizer and Moderna vaccines — it typically takes a few weeks after vaccination for the body to build immunity against the virus that causes COVID-19. Once people have developed immunity, they are protected from getting seriously ill.
The vaccines are slightly less than 100% effective. In clinical trials, the Pfizer vaccine showed an efficacy of 95% at preventing symptomatic COVID-19 infection after immunity is fully developed; the Moderna vaccine showed 94.5% efficacy; and the Johnson & Johnson vaccine has proven to be 72% effective against moderate to severe COVID-19 illness in the U.S. However, all three vaccines were determined to be 100% effective against hospitalization and death, the most important measure of efficacy.
We don’t know how long immunity lasts. Because COVID-19 is a new disease and the vaccines were developed over the past year, the length of time that each of the three vaccines offer protection against moderate to severe COVID illness is still uncertain. Like the flu vaccine, people may need to receive annual COVID-19 vaccination to have continued protection from illness. Research is ongoing so more will be known in the coming months.
Practice post-vaccination precautions
It’s important to note that while vaccination can protect people from getting moderate to severe COVID-19 illness, it’s not known whether it prevents people from spreading the disease to others. Experts believe that it might require 75% to 80% of the population being vaccinated to reach herd immunity, reducing the risk of infection passing from person to person.
Until then, everyone — whether they have been vaccinated or not — should continue to wear a face covering, avoid crowds, maintain 6 feet from others not from their household, and wash their hands often.