UPDATED: Aug. 26, 2020 — 5 p.m. EST
It’s back-to-school season and schools across the country are taking different approaches. Some are holding in-person classes on a rotating basis and others have gone fully remote. In addition, many workplaces are reopening, despite there still being high levels of new cases and deaths around the country. One big factor that’s driving reopening plans is immunity. Is it possible to be immune from COVID-19? And if there is immunity, how long does it last? It is more important than ever to understand how immunity to the coronavirus works and the implications to a reemerging public.
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The Journal of General Virology published an article on May 20, 2020 aiming to answer some of these questions. The paper is a review, meaning it gathers together information from multiple other studies. A lot of the information detailed in these studies comes from knowledge of the six other coronaviruses that have been discovered. That’s right — the virus causing COVID-19 is not the only coronavirus out there. There are four coronaviruses that circulate seasonally and cause the common colds and two viruses (SARS-CoV and MERS-CoV) that, like SARS-CoV-2, have crossed from animals to humans. These other coronaviruses have been studied in much more detail than the current virus and can be used to make inferences about SARS-CoV-2 based on their genetic similarities. The authors of the article explained to Science Daily:
“SARS-CoV-2 is a new virus in humans and because of this we are having to learn quickly many of its basic properties. In the absence of such data right now, we can try to make predictions about the immune response to SARS-CoV-2 by re-examining what we know about the two epidemic coronavirus of humans, SARS and MERS and the four seasonal human coronavirus. We need to be cautious about inferring too much, but it is a good place to start.”
Why Study of Antibodies Is Important
The big buzzword relating to COVID-19 immunity is antibodies. Antibodies are proteins formed by blood cells when faced with a virus, bacteria, or foreign material (like pollen). These antibodies stick around in your blood for varying lengths of time and help fight off that virus, bacteria, or foreign material if they encounter it again. However, not all antibodies are protective. Some can actually make the illness worse by causing inflammation. There is still work to be done to see which types of antibodies help protect against reinfection with SARS-CoV-2 and which do not.
The review from the Journal of General Virology cited a few studies that look at antibodies to MERS and SARS in the months and years following infection to figure out immunity. When looking at these viruses, the studies showed that functional antibodies (which may give you immunity) could remain for at least 34 months for those who had severe infections. However, those antibodies did decrease over time and were minimal for those with mild or asymptomatic initial infection. One study showed that the antibodies reduced by 75% by three years and a majority of those studied had “extremely low titers,” meaning that the antibodies would have little to no ability to protect a person from reinfection.
In other studies looking at the seasonal coronaviruses (those that cause the common cold), it was found that most children have antibodies against the seasonal viruses, yet these viruses accounted for 22% of acute respiratory illnesses in adults. This means, even if you have immunity to these seasonal coronaviruses at one time, the immunity is not permanent and you can still get the virus down the line.
Can COVID-19 Antibodies Give Me Immunity?
While previous studies on coronaviruses might provide some guidance, nothing beats studies involving the actual virus of interest. There have been some very recently published papers and non-peer reviewed preprints (potential future papers) regarding COVID-19 antibody responses. But since this virus is so new, all the data is still in its beginning stages. These studies have shown that the immune response to the most recent coronavirus is similar to that for SARS and MERS. Most infected individuals do show an antibody response 10-14 days after symptom onset, but these can be low or undetectable in mild cases. There is not enough data yet on how long the antibodies remain and if they will fight off reinfection. Interestingly, like SARS and MERS, severely ill patients had a higher antibody count compared to non-severe cases in the short term (7-14 days post symptom onset). However, 15-21 days after symptoms there was no difference in this count. This means that the antibody count for severely ill patients wanes quickly and beyond 15 days they have the same potential antibody protection as those who had mild illness.
What all the studies show is that most people infected with SARS-CoV-2 do have an antibody response between 10 and 14 days after infection, meaning there most likely is a level of immunity, at least in the short term. There is not a lot of information about how long these antibodies to SARS-CoV-2 last, but if you extrapolate information from SARS and MERS, we know that the antibodies wane over time and some people were re-infected in as little as 80 days. This is important to keep in mind as the world begins to reopen. Fortunately, new information is being discovered daily about immunity to SARS-CoV-2 and all this data being used to develop and test safe and effective vaccines. In the meantime, if you believe you have already had the virus, it does not exempt you from taking all precautions provided by the Centers for Disease Control and Prevention (CDC). It is still important to follow their recommendations including social distancing, wearing a mask in public, and frequent hand washing.
What about reports of people getting the virus twice?
If you’ve been paying attention to the news, there have been some reports of people testing positive for SARS-CoV-2 twice. At first, it may sound like these people were infected a second time. However, there is a more likely scenario: These patients were infected with the virus once and their symptoms have since resolved, but a small amount of the virus is still present in the body. Therefore, when the patients got tested weeks later, the tests still came back positive (because they were picking up the same virus that had been there since the first infection). In fact, according to the CDC, people may continue to test positive for the virus for three months after infection.
On the other hand, in late August 2020, the first true case of SARS-CoV-2 reinfection was reported. A man from Hong Kong was found to have the virus for a second time — and genetic analysis of the virus confirmed it was likely a different strain than he had the first time. The man did not have any symptoms the second time he was infected. Since this is only the first confirmed case of reinfection occurring so far, it’s hard to draw any conclusions about what it means for other people. Of note, the Hong Kong man did not have any antibodies after the first time he was infected, so it’s impossible to tell what role antibodies (or the lack thereof) played in his second infection.
What about T cells?
If you’re familiar with the body’s immune system, you may be aware that antibodies aren’t the only way we are protected against foreign invaders. T cells — a type of blood cell — can also recognize and remember pathogens like viruses and bacteria.
There is currently some research indicating that T cell immunity may play a role in COVID-19. For example, people who have been exposed to other coronaviruses in the past (such as one of the four coronaviruses that cause the common cold) may have a degree of T cell immunity that can help fight against SARS-CoV-2. Like antibody research, this research on T cells is still in its infancy and it’s too soon to say whether T cells can actually protect against COVID-19 or not. Check back to Dr. Oz’s COVID-19 center for updates as we learn more.