Stories like this will become more common as millions of Americans receive the Pfizer-BioNTech and Moderna vaccines over the coming months. Over time, many vaccinees will continue to be infected with the novel coronavirus.
During the trials, the vaccines were found to be around 95% effective, meaning that some people who were vaccinated were still infected.
Here’s how and why:
IMMUNITY IS NOT EFFECTIVE
Vaccines take time to build immunity, and the two licensed coronavirus vaccines both require two doses, spaced several weeks apart, to train the body’s immune system. People can be exposed to the coronavirus just before they are vaccinated, or right after, and the body will not have time to develop its defenses.
The Centers for Disease Control and Prevention says building immunity “typically takes a few weeks.”
“This means that it’s possible for a person to be infected with the virus that causes COVID-19 just before or right after vaccination and still get sick,” the CDC says.
The 95% efficacy number for COVID-19 vaccines also assumes some built-in wait time. Moderna measured the effectiveness of its vaccine from 14 days after the second dose, while Pfizer measured it from seven days after the second dose.
VACCINES MAY NOT OFFER PERFECT PROTECTION
No vaccine is 100% effective and manufacturers of coronavirus vaccines are still evaluating whether vaccines protect against all infections, or just those that cause symptoms.
The CDC estimates that 40% of coronavirus infections do not cause symptoms, and trials of the Moderna and Pfizer / BioNTech vaccines only looked at whether the vaccines prevented symptomatic infections.
Moderna said in December that it submitted data to the US Food and Drug Administration showing that its vaccine prevented 2/3 of all infections, including asymptomatic infections. For now, the CDC recommends that people don’t assume they are fully immune to the infection after being vaccinated.
Overall, the two vaccines provided about 95% protection in clinical trials – so a small number of people could still catch the virus even after two injections. In wider use, this rate of effectiveness may decline as people with varying levels of immune system response get vaccinated and then travel to the world.
IT’S NOT BECAUSE THE VACCINE GIVEN YOU THE VIRUS
Current coronavirus vaccines cannot infect anyone with the virus. They do not contain the virus.
Instead, they carry a small stretch of genetic material called messenger RNA or mRNA. It asks cells in the body to make a small piece of material that looks like part of the virus. These bits, in turn, are recognized by the immune system as a foreign invader, and it begins to make antibodies and immune cells that can recognize and neutralize the virus if the vaccinated person is ever exposed.
“None of the approved and recommended COVID-19 or COVID-19 vaccines currently in development in the United States contain the live virus that causes COVID-19. This means that a COVID-19 vaccine cannot make you sick with COVID-19, “the CDC says.
IMMUNITY MAY RELEASE OVER TIME
No one knows how long vaccines will protect people from infection.
The new coronavirus has only been around for about a year, and the final stages of vaccine testing were only completed a few weeks ago. Pfizer and Moderna followed the volunteers for at least two months after their second doses.
The protection provided by vaccines may wear off over time, and some vaccines require a booster shot years later. For example, the CDC recommends that adults get the tetanus vaccine every 10 years. During measles or mumps outbreaks, the CDC says some people “may be referred” to get an extra dose of the MMR vaccine for extra protection.
It is also possible that the new coronavirus mutates in a way that makes vaccines less effective. The flu virus strains are constantly mutating and this is one of the reasons people need fresh flu shots every year.
Doctors hope the coronavirus doesn’t mutate like the flu. If that happens, however, the technology used to make the new coronavirus vaccines is designed to be easily adapted. Updating Moderna and Pfizer vaccines is expected to take much less time than manufacturing new influenza vaccines.
OTHERS MAY NOT BE SURE
Dr Anthony Fauci’s health officials are warning people that no one can get rid of face masks and social distancing behavior just because they have been vaccinated.
This is because even people who are themselves immune to the virus can be exposed to it and pass it on to others. It can grow in the nose, says Fauci, director of the National Institute of Allergy and Infectious Diseases.
“It’s possible that someone could get the vaccine but could still be an asymptomatic carrier,” said CNN medical analyst Dr. Leana Wen, an emergency physician. “They may not have symptoms, but they have the virus in their nasal passage, so if they talk, breathe, sneeze, etc., they can still pass it on to others. ”
Given these unanswered questions, the CDC says those vaccinated should always use “all the tools we have” to stop the pandemic, including wearing a mask and staying at least 6 feet from others.