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On Tuesday, Paul Offit, the vaccine developer and a professor of pediatrics at Children’s Hospital of Philadelphia, dropped by, virtually, for a conversation with STAT+ subscribers. During the discussion, he addressed a question on everyone’s mind: How worried should we be about new variants of SARS-CoV-2, the virus that causes Covid-19?

Offit — who, overall, believes “we’re going to turn the corner,” with the help of vaccines — had plenty of worries. A rare side effect of the vaccines could emerge and scare people away from them, even when the benefits far outweigh its risks. It could take a long time to fix vaccine distribution and manufacturing problems.

But he said his biggest concern is that a new variant of the SARS-CoV-2 virus will learn to evade the vaccines. He also explained, at length, why he doesn’t think it’s time for you to worry yet. The transcript of that explanation follows; it has been edited for clarity and length.


Offit: So this is a bat coronavirus — it’s not a human coronavirus — that made its debut in the human population in November 2019. It will adapt to growth in humans, and when it adapts, it will create variants. It created a variant the minute it left Wuhan, the so-called 614 variant, which was somewhat more contagious. Since then, it’s created at least four variants that we know of — the U.K. variant, the South African variant, the Brazilian variant and then, just in the last few days, the California variant.

So the critical question is not are variants being produced. Of course they’re going to be produced. The critical question is do these variants make the virus more contagious, more virulent, and most importantly, far and away most importantly, have these variants evaded recognition by vaccine-induced immune response? That’s the critical question.


Here’s what I would say. It looks like the U.K. variant is somewhat more contagious. The good news is it’s still spread by small droplets, so masking and physical distancing still work. I don’t think there’s good evidence that the U.K. variant is more virulent. If you look at people who are hospitalized in the U.K., you are no more likely to die if you’re hospitalized with a variant strain or not. That may change over time.

The critical question is, have these viruses mutated away from the vaccine? The way you’re going to know that, the proof for that, is when you see people who have gotten two doses of vaccine who are then hospitalized and who are shown to be infected with a variant strain. That’s the proof. Everything else that we’re looking at is just a way to predict whether or not that happens. And the predictions are not perfect.

So, for example, if you look at the U.K. variant, both Pfizer and Moderna have taken serum from people who were immunized with their vaccines and shown that those sera neutralize the U.K. variant in the same manner that they neutralize the non-variant viruses. So therefore one should be reassured.

But if you look at the South African variant, it looks like when the companies take the sera from people who were immunized with their vaccines and see whether you can neutralize that South African variant in the laboratory, it shows that there’s a decreased capacity of those antibodies that are obtained from people who are immunized to neutralize that virus. Now, it’s unclear what that means. Just because you have a lesser capacity to neutralize that virus doesn’t mean that you’re not still protected. Because we don’t really know the level of neutralizing antibodies that’s associated with protection. Even though it’s a lesser response, that doesn’t mean it’s still not an adequate response.

The second thing is you’re just looking at one aspect of the immune system, which is neutralizing antibodies. There are other aspects of your immune system that are associated with protection. One is called T-helper cells, which are a kind of T cells that actually help your B cells make antibodies. And those are much more broadly cross-reactive. The second thing is so-called cytotoxic T cells, which are T cells that kill virus-infected cells. All three of those parts of the immune system are important for protection or at least amelioration of disease. And we’re only looking at neutralizing antibodies when we’re doing these studies.

So I would say, don’t worry yet. We don’t really have any evidence that people who have been given two doses of these vaccines are at greater risk. We’ll see what happens with the South African strain. Interestingly, studies of unapproved vaccines are being done now in South Africa. So we’ll see whether or not people who get those vaccines in South Africa are relatively protected against this strain. We’ll know this over time. But I would say don’t worry yet.

  • Additionally, the classic pattern of viral mutation is more contagious, less harmful. I know the Brits think their varient is slightly more lethal. But, I suspect, and they’ve even postited, that the higher mortality is due not to the varient’s effects on the body, but the overwhelmed health care system causing a drop in the quality of care.

    Viruses mutating to become more deadly just defies the classic pattern of viral mutation. It defies evolution. A virus doesn’t want to kill you. It wants you to not even notice it, so it can reproduce and spread freely. The host dies, the virus dies. The host slows down due to severe illness, the virus doesn’t spread as quickly or as far.

    • I think the analyses of the UK transmissibility compare like with like – both variants are circulating at the same time so the patient data comes from the same time period and hospitals. So any decrease in standard of care should have affected both classes equally. Also, the virus doesn’t ‘want’ anything, it just mutates and a mutation that increases spread will get preferentially selected. So yes, if it mutates to a form that kills very quickly it won’t spread as well. But if it mutated to a form that spreads much better because of higher viral load, the higher load could well make one sicker. If the increased transmissibility outweighed the effects of increased sickness then a more lethal mutation could be selected. It’s not a iron rule that they get weaker.

    • Not sure where you are getting your nonsense theory. You are spreading false information. In the Spanish Flu, the virus mutated to be more deadly and killed more people during the second waves.

      The theory that virus want to multiple and not kill its host is nonsense. Looks at ebola.

      Also, by the time the host died, the virus has already spread to someone else. Virus are meant to kill. That is the meaning of their existence. The are like organic programming that follows a certain instructions.

      If you have more virtual load, that means more of your cell get damage or killed by this virus. How is that not more deadly ?

      Please stop you harmful and misguided theory.

  • Considering that there’s evidence that even infaction from similar known coronaviruses can train your T & B cells to fight SARS-COV-2, protecting you not from infection but from disease, from the severe effects, then I think it logical that at worst, the vaccines or prior infection to an earlier varient would leave you with B/T cell protection.

    In the end that’s what matters. Who cares if everyone gets infected as long as it’s not dangerous? We’re infected by harmless viruses all the time without even knowing it. We don’t need to eliminate SARS-COV-2. We need to eliminate COVID-19.

  • I am concerned that people are still not taking this seriously enough. The reason these variants occur is that everyone infected is like a mini lab allowing mutations. The more infected, the more chance for mutation. Also there is currently no evidence that vaccination prevents spread as scientifically you need secretory IgA for this. Also secretory IgA seems to only last about 2 months. Everyone needs to be vaccinated or they are likely to get the disease.

  • Michael Osterholm is worried that the new variants will explode in the population faster than we can get people vaccinated. His fears seem grounded in reality. I am worried, too–not so much that the vaccines will not be effective, but that enough people will be able to get them before it is too late and before our health systems become overwhelmed in a way we’ve never seen before. I hope this is wrong, but it seems that this may be our current trajectory.

  • “Don’t worry it will probably be like SARS 15 years ago, the Chinese are sensationalizing the situation. It will probably burn itself out in a couple of weeks.”

    Is what a lot of “experts” were saying last year in January, as a mysterious disease caused by a new(novel) coronavirus began to spread worldwide. And instead of a few hundred fatalities(from SARS) over several months, we now have millions around the globe as this new disease suddenly became one of the leading causes of death in many countries.

    “Not worrying” and not preparing for the worst case scenarios is what got us here. Overreacting is better than not reacting when dealing with pandemics. If medicine, attitudes, reactions, and conditions were the same as 100 years ago we would probably be dealing with comparable numbers of deaths as the 1918 Flu Pandemic.

    Actions need to be taken to introduce(test and approve) new versions of current vaccines or some type of booster of a monoclonal antibody treatment to eliminate any defenses the virus develops as soon as they are detected, not when it is too late… again.

  • I’m worried because I have friends in Haiti. For unknown reasons, the country seems to have fewer covid infections than known variables would predict. My concern is that, depending on the interaction between some hidden aspect of the epidemiology and any potential shocks to the dynamics, that the country might experience an (informally specified) phase transition into a much deadlier epidemic.. without any reasonable chance that any vaccine might make a difference in any reasonable time. So under those conditions.. shouldn’t we rather be very worried indeed?

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