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The first data from an ongoing study in the UK is causing a wave of alarm about the pandemic this week. It found evidence that levels of antibodies to SARS-CoV-2 dropped sharply in the general population of England over the summer, raising fears that immunity to Covid-19 may start to decline significantly in as little as three months.
Although the study findings are relevant, they are not as scary as they seem. These types of studies alone cannot tell us if immunity wears off so quickly and, more importantly, antibodies are not the only factor that determines immunity to infectious diseases like COVID-19. Other research, including a study just published today, suggests that our most important antibodies to COVID-19 are not as endangered as the UK study indicates.
Researchers at Imperial College London, with government help, have been conducting the Real-Time Assessment of Community Transmission, or REACT, has been studying in England since the beginning of the summer. One part of the project focuses on coronavirus antibody levels in the community, asking people to use take-home tests that collect a finger stick blood sample. This week, on the preprint medRxiv website, researchers released preliminary data from the study, involving more than 350,000 residents.
In late June, they found that about 6% of the volunteers tested positive for these antibodies. But in September, that number fell to 4.4%.
“On the balance of the evidence, I would say that, with what we know about other coronaviruses, it would appear that immunity declines at the same rate as antibodies decline, and that this is an indication of waning immunity at the population level,” Wendy Barclay, Head of the Department of Infectious Diseases at Imperial College London, saying reporters at a conference announcing the results this week.
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Barclay is absolutely correct in pointing out that our immunity to other coronaviruses fades over time. Experts have long said that the same thing will likely happen to the coronavirus that causes covid-19, at some point. But beyond that, immunity to any specific disease can be a difficult knot to unravel. And while these results may be robust, given the large sample size, the implications for our immunity to COVID-19 are not that clear.
For one thing, it is perfectly normal to see the levels of antibodies against any fresh germ decrease over time. So seeing this decline in the last three months is not, in itself, proof that immunity will go away in that time frame. The other consideration is that not all antibodies are the same. The most important ones are called neutralizing antibodies, because they can directly prevent something like coronavirus from infecting new cells. Even if our coronavirus antibody levels drop in the short term, most of us may still have enough neutralizing antibodies to stop reinfection for a while longer.
This afternoon, a new study seems to show that the same thing is happening. The study, published in Science, analyzed antibody levels among 30,000 New Yorkers diagnosed with mild to moderate Covid-19. After three months after infection, the researchers continued to find a stable level of neutralizing antibodies in more than 90% of their volunteers; in a subset of volunteers seen five months after their illness, levels had only dropped slightly.
“Although this cannot provide conclusive evidence that these antibody responses protect against reinfection, we believe that it is highly likely that they decrease the odds ratio for reinfection,” the authors wrote.
As experts have saying Gizmodo previously, a person’s current antibody levels are not the only relevant factor in determining immunity. Our immune system also has memory B cells, which wake up the rest of the immune system when they detect a reappearing germ, including increased antibody production. This generally results in a much faster immune response the second time around. Besides that, there are certain T cells that “remember” a past germ and go into action when it tries to reinfect us. These other components may not completely prevent coronavirus reinfection, but they should generally make the second infection much easier for the body to handle.
This is all very complicated, and there are many things about our immune response to the coronavirus that we are only now beginning to understand (not to mention how these responses will affect the effectiveness of a vaccine).. Unfortunately, there have been several reports of confirmed reinfection in various countries, including the US. Some But not in most of these cases, the person got much sicker in the second round and at least one person died from reinfection. But many experts do not believe that these reinfections are occurring en masse at this time, although the necessary data to confirm the frequency with which they occur is still lacking.
The main conclusion here is that we must be careful when jumping to conclusions about any scary-sounding antibody study. It remains true that aspiring to “herd immunity” is a ridiculous and dangerous idea, but even more so because it will lead to many preventable deaths and illnesses, not because we all become re-infected in a few months.
In fact like me famous in June, the most present danger of covid-19 continues to be the first outbreak of infection. Even though the US is now in the midst of its third major pandemic peak, the vast majority of Americans, and indeed people around the world, still I do not have caught covid-19 yet. Hopefully, most of us never will.
