Do Vaccines prevent severe disease and death? Yes and No
An exit strategy using vaccines and social action.
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An exit strategy using vaccines and social action.
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The power of the vaccines has been a dramatic success in humanity’s fight against COVID. There has, however, crept into our conversations a misunderstanding about their effectiveness against severe disease that should be addressed.
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Originally, the studies of vaccines tested their action against severe disease and found 90-95% efficacy of the Pfizer and Moderna vaccines. The high efficacy translates into a 10 to 20 fold reduction in severe disease.
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This is an important success. What was not measured and therefore not known at the time was how effective they are against transmission of the diseases to cause mild cases.
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Since then we learned a second piece of important good news, which is that transmission is also stopped at about the same rate of 90-95%. This means that vaccines can be used not only to prevent severe disease, but also to prevent transmission, reducing the number of cases.
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There is a however: if you do catch the disease, the similar reduction in transmission and severe cases, means that the cases that do arise, the “breakthrough” cases, are about as severe as the original ones.
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If the number of new cases goes down by a factor of 10 and the number of severe cases goes down by a factor of 10 then the fraction of new cases that are severe doesn’t change. Given uncertainties in the data there may be some difference, but it is not huge.
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So breakthrough cases are still subject to hospitalizations and deaths basically the same as the original cases without the vaccines. This means that we cannot double count the effectiveness of the vaccines.
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Vaccines are highly effective at reducing severe disease and death relative to the original unvaccinated state, they are highly effective at reducing transmission, but if you do get a case that case can be severe and be fatal.
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The risk reduction of about a factor of 10 or 20 assumes that people’s behavior doesn’t change. If behavior changes (reduced mask wearing and social distancing) the risk goes up again. How high does it go?
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We don’t know exactly because the question is whether the risk is associated with the strength of the immunity for an individual with some having low and others higher protection. If so, it remains strong even with changes in behavior.
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On the other hand, if the efficacy depends on the strength or frequency of exposure, then the rate of infections goes up with changes in behavior. Risk would accumulate over time. In that case, ongoing exposures could undermine the increase of effectiveness.
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That wouldn’t be much protection at all.
So next time someone tells you we don’t have to worry about getting a severe case when you are vaccinated, don’t believe them. If the risk is lower by a factor of ten, you likely still don’t want to get a severe case or die from it.
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So next time someone tells you we don’t have to worry about getting a severe case when you are vaccinated, don’t believe them. If the risk is lower by a factor of ten, you likely still don’t want to get a severe case or die from it.
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You may also not want to suffer long covid consequences (which we still don’t know how they are for breakthrough infections).
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And by the way. The variant first found in India is showing an increased ability to breakthrough the vaccine protection. Preliminary data say by about a factor of 2. This degrades the vaccine protection and we don’t know what the next variant will do.
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On the other hand, the prevention of transmission opens an outstanding possibility. Elimination. The basic calculation is that with a R of 5 (including superspreader events) for the original variant, and a reduction of 10X we can have an R well below 1.
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Of course, this is where people calculate how high a percentage we need to get R<1 so as to achieve “herd immunity” but the herd immunity calculations ignore the reduction of R that we can achieve using other measures.
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We can overcome the challenge of the level of vaccination by combining efficacy of vaccines with other measures like limiting gatherings and mask wearing. Avoiding the strongest social measures (including lockdowns) we can still achieve elimination locally and then globally.
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Taken together, vaccination along with social distancing, testing, isolation, and travel quarantines, can reduce the number of transmissions to zero within a short time, as is within reach in Israel.
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Surely this is with less effort than without the vaccines, this still takes patience in opening up. The faster we achieve elimination the sooner we can be without risk for everyone.
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There will be fewer cases. There will be less risk we will have vaccine evading variants that will make it harder by increasing R both because of higher transmissibility and because of partial or complete vaccine evasion. And there will be lower economic impacts.
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