What Happens If You Have COVID When You Get the Vaccine? Scientists Explain

Getting a COVID vaccine while infected with the virus may not cause harmful effects, scientists have said—but it could cause the vaccine to be less effective. Google search trends show U.S. citizens are wondering what would happen if they were to receive the shot while already ill with COVID.

It is important to note that the U.S. Centers for Disease Control and Prevention (CDC) states that people should not get a COVID vaccine if they are ill with COVID symptoms, and says they should wait until they meet the criteria for coming out of self-isolation.

This advice also extends to people who are not showing symptoms, but are having to quarantine because they came into contact with someone who does have COVID.

Dr. David Margolius, an internal medicine specialist at MetroHealth, told Ohio news network Ideastream: "The reason we ask people to wait until they have recovered from COVID before getting the vaccine is to keep all the health care workers and others safe during the process."

Whilst it is important to quarantine when necessary to prevent COVID spread, scientists have said that if a person were to receive a vaccine while infected with COVID, it would not necessarily cause harmful effects—though this may depend on whether they are showing symptoms and how severe the symptoms are.

Robin Shattock, head of mucosal infection and immunity at Imperial College London, told Newsweek the shot might be less effective if it is given to someone showing severe COVID symptoms. He said: "It is possible that if someone got the [shot] when they had more severe symptoms that the vaccine taken might be less effective."

This point was echoed by Dr. Thaddeus Stappenbeck, chair of the Cleveland Clinic Lerner Research Institute, who told Ideastream it would not make people sicker or less sick, but the vaccine could be less effective if someone gets a shot while they have symptoms.

However, Shattock added: "There is no scientific reason to think there would be any additional safety concerns with getting the vaccine during asymptomatic infection, which I suspect is the primary concern of those doing the searches.

"There is some argument that getting the [vaccine] might accelerate the immune response relative to natural infection, in which case it might prevent severe disease in those that might have gone on to be ill if they'd not got the [shot]."

Al Edwards, an associate professor in biomedical technology at the University of Reading in the U.K., said it is statistically likely that some people infected asymptomatically with COVID will receive the vaccine due to the scale of rollouts. Asymptomatic infection means the person has the virus but is not showing symptoms, and may not know they have it.

He told Newsweek: "I don't think anything would really happen much differently, biologically speaking, except there could be a few outcomes; you might get faster recovery, if the vaccine is able to prime your immune system fast enough to help you respond to the infection.

"You might get a better immune response to the vaccine, if the natural infection drives even better response by providing virus to respond to as well as the vaccine.

"The immune system is super-clever and very robust so it's improbable that anything negative would happen. We also know you can mix different vaccines and get equally powerful responses even if you combine 4 or 5 different vaccines, so there is no worry about the immune system being 'overwhelmed.'"

While the CDC advises against people getting vaccinated if they are in quarantine or self-isolating with COVID, it says people should still get vaccinated once they recover—and after 90 days if they were treated with monoclonal antibodies or convalescent plasma, to be on the safe side.

Megan Macleod and Georgia Perona-Wright, both senior lecturers in immunology at the University of Glasgow, Scotland, said it is important for people to get vaccinated even if they have already had COVID in the past.

They told Newsweek in a joint comment: "It is still important that people who have been infected are vaccinated. This will boost their immune response against SARS-CoV-2, giving them more and longer-lasting protection.

"The immune response to any pathogen gets better each time you are exposed to it through infection or vaccination—this is why we often give booster vaccines, e.g. for tetanus."

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COVID vaccine
A member of staff uses a needle and a phial of Pfizer-BioNTech Covid-19 vaccine to prepare a dose at a vaccination health centre in Cardiff, South Wales on December 8, 2020. Scientists say people should get a vaccine if they have previously been ill with COVID and recovered. Justin Tallis/AFP/Getty