Pandemic Perspective #41  April 3, 2021

Why vaccines don’t always work

            Vaccines have never been without controversy since the first one appeared at the end of the 18th century. The permutations of that first smallpox vaccine led to the total eradication in the 1970s of one of the most terrifying of human afflictions, one that sometimes killed half of its victims and left many of the rest with characteristic pitted facial scars.

            The COVID-19 vaccines that have now been given to more than half a billion (!) people appear to have a protective effect in as many as 95 percent of vaccinees. Why not 100 percent? There are multiple reasons and they apply to all vaccines in one way or another.

            Reason #1. After more than half a century we still don’t have an influenza vaccine that is completely effective or whose protection lasts more than a few months. That virus undergoes mutations in those structures that are the targets of the vaccine so that a new preparation needs to be produced nearly every flu season. The SARS-CoV-2 virus that has upended the global economy mutates too but those changes – at least for the moment – are not of the type that negate the effectiveness of the vaccine.

            [Note: as of this writing there have been no deaths attributed to the current vaccines and no COVID-19 deaths among persons who are at least one month post-vaccination. That too might change by the time you read this but the numbers showing its safety remain overwhelming.]

            Reason #2. The human immune system is enormously complex and some persons are genetically missing a key component. An example is that some persons are incapable of forming antibodies against the diphtheria vaccine. However the redundancy of the immune system probably covers for that defect.

            Reason #3. Obesity and diabetes (type 1 and type 2) reduce the effectiveness of the immune system. The high incidence of obesity (nearly 40 percent) and type 2 diabetes (more than 12 percent) undoubtedly limit the protection afforded by the vaccine in these groups.

            Reason #4. Using a standard needle in an obese person can put the vaccine into fat, not muscle. This not only can make the vaccine ineffective it can lead to complications such as abscess formation. Some health facilities now use needles in obese persons that are twice as long as those used for those who appear to be of normal weight.

            Reason #5. Improper storage. Some COVID-19 vaccines require ultra-cold freezers to maintain potency.

            After the measles vaccine became available in the 1960s some children developed the disease in spite of having been vaccinated. Some medical offices had stored the vaccine in the door shelves of the refrigerator, where the temperature was too high, severely reducing the potency of the vaccine.

            Reason #6. Aging reduces the strength of the immune system. That’s why there exists a high-potency influenza vaccine for seniors. We don’t yet know if this will be a problem among our oldest old in this pandemic but it will require monitoring.

            Reason #7. Timing. The measles vaccine is not given to children until the age of  12 to 15 months. Prior to about 1985 most women had had natural measles infection and they transferred protective antibody to their infant that persisted for several months. A measles vaccine given too early might be ineffective, hence the delay. None of today’s mothers born in the U.S. have experienced natural measles and vaccine antibodies do not last as long as those induced by wild measles virus. For that reason, infants above the age of six months that are exposed during an outbreak should receive the vaccine.

            Coronavirus infections are common during the preschool years, less so afterwards. Existing natural antibody may help to explain why children rarely become seriously ill from the COVID-19 virus but it could reduce the effectiveness of the vaccine. Vaccine trials in children are only now being done and the vaccination of children will probably begin this summer. How they will respond won’t be known for at least another year.

            Vaccine failure is common, it is not unexpected and it should not be a reason for not accepting the vaccine. If you are willing to take a chance on being killed while driving your car you should be willing to take a chance on the vaccine. I’ll bet on the vaccine every time.