More than 21 million Americans have been officially diagnosed with COVID-19, but the real number is significantly higher. The vast majority have recovered and now have antibodies circulating through their blood that protect them from getting sick again.
If you’ve been infected with SARS-CoV-2 before, you might naturally wonder if there’s any point in taking a vaccine. Although this is something that studies in the future will be able to answer thoroughly, the short answer is ‘yes’, you should still take a vaccine if available and if there aren’t other, more vulnerable people waiting in line.
You’re protected from future COVID-19 infections after you become sick — but this natural protection doesn’t last forever nor is it uniform
In fact, scientists aren’t yet sure how long both naturally and vaccine acquired immunity against COVID-19 lasts.
“We do not know how well and how long naturally acquired immunity provides protection,” Hildegund Ertl, Professor at the Vaccine & Immunotherapy Center at the Wistar Institute, told ZME Science.
The good news is that we can expect natural immunity to last for at least a couple of months. A recent study published in December that involved more than 12,000 healthcare workers in England — by far the most exposed group of people to the coronavirus on a daily basis — showed that those who were infected with SARS-CoV-2 continued to produce antibodies against the virus.
This protection should last at least over the several months that the study was conducted (April to November). According to the same study, just three people out of more than 1,400 antibody-positive individuals subsequently tested positive for SARS-CoV-2. Not one of them had any symptoms of the disease.
Along with other studies, these findings suggest that, at least for the first few months, the risk of reinfection is extremely low.
Natural immunity may wane
There’s nothing surprising in any of this because this is simply what is supposed to happen. Nevertheless, there are still good reasons to get vaccinated.
First of all, at this stage of the pandemic when there are vaccination bottlenecks, if you’ve been sick recently, it’s best you let others take the shot before you.
However, if you had COVID-19 several months ago, a vaccine could boost any inconsistencies in immunity. For instance, we know from other common coronaviruses that cause common colds that antibody levels in response to these viruses wane rapidly. Whether that’s the case for SARS-CoV-2 remains to be seen. What’s certain is that cases of reinfection truly exist.
A small number of infected people may not develop long-lasting immunity after recovery, especially if they weren’t very sick the first time. This can have to do with differences in the amount of coronavirus they were exposed to. The most severe symptoms of infection often lead to higher levels of neutralizing antibodies, so a person with very mild symptoms or no symptoms, in theory, is less protected than someone who recovered from a severe illness. The best safeguard around this individual variability is vaccination — this essentially levels the playing field for almost everyone.
The uncertainty surrounding the length of natural immunity is why vaccination should eventually be performed regardless of the history of coronavirus infection. This is to ensure that a large enough percentage of the population is immune to SARS-COV-2 at the same time in order to achieve herd immunity. When herd immunity occurs at a global level, this pandemic is officially over.
And if you were wondering, the clinical trials for the Pfizer vaccines involved participants who were later found to have neutralizing antibodies. The vaccine was just as safe for them as in people with no history of coronavirus infection.
The Centers for Disease Control and Prevention (CDC) in the United States advises people with a history of COVID-19 that they may wait 90 days after their prior infection to get vaccinated, if they’d rather not have it immediately.
Vaccination may boost immunity (without serious risks)
The Pfizer and BionTech vaccine was found to be 95% effective at preventing COVID-19 in phase 2 and 3 clinical trials that involved tens of thousands of people. As well as lowering the risk of infection in people with no prior history of infection, these studies also found that the vaccine prevents reinfection in people who have already been exposed.
When people who already had COVID-19 get vaccinated, their immunity is essentially topped up, hopefully increasing the length of immunity.
Although this has yet to be proven, vaccine immunity may also be more robust than natural immunity. However, it’s not at all clear if vaccine immunity lasts longer than natural immunity following disease.
So, as long as the vaccine is readily available, the benefits of taking a vaccine far outweigh the small risks involved, which include mild and short-lived side effects (i.e. mild pain around the injection site, fatigue, or headache).
There’s one situation in which you should not take a vaccine: if you’re currently sick with COVID-19.
Per CDC guidelines, if you’re already sick with a coronavirus infection, you’re advised to wait until you recover from acute illness (until symptoms fade) and you’ve completed the quarantine period. For most people, that’s 10 days after the onset of symptoms.
BOTTOM LINE: if you’ve recently been sick with COVID-19, your natural immunity should prevent subsequent infections. If infection occurred many months ago (i.e. six months), or if the symptoms were very mild, natural immunity may not be enough to prevent a potentially contagious infection, while vaccination should offer more robust protection.
This article is part of a series by the ZME Science editorial staff meant to inform and educate the public concerning the coronavirus vaccines. This is not medical advice. You should consult your doctor before making a health decision based on information you read online.