Vaccine Boosters: A Tutorial for New Parents

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Being a new parent, or an expectant parent can make you particularly aware of health issues, especially during the pandemic that we have endured over the past year and a half. As efforts continue to get more people vaccinated against SARS-CoV2 (the virus that causes COVID-19), you may be hearing discussions and debates surrounding the issue of vaccine booster shots, so let’s unpack that.

If you are up to date on your various non-COVID immunizations —as well you should be— that you know that typically you receive more than one shot of each vaccine. After the initial immunization that occurs when you are young, to prevent certain conditions, tetanus for example, you need to have a booster shot every certain number of years. The reason is that immunity tends to wane as time goes on, if you are not exposed to the disease-causing entity that the vaccine is designed to counter. This is the result of your immune system doing a kind of cost benefit analysis. Just like keeping all of you electrical appliances, heating, and air conditioning systems going 24/7 would take a high amount of energy, so would keeping up full time production of antibody producing B lymphocytes specific for each disease-producing entity. Rather, to save energy and resources, once it has learned to recognize each disease causing entity, the immune system makes and circulates only a minimal number of special cells, called memory B cells. Acting like advanced scouts, memory cells evolved for each particular entity will respond if that entity is encountered. This will result in the rapid production of many more B lymphocytes and T lymphocytes able to work with still other immune system cells and components to neutralize or destroy the disease causing entity. However, such memory response systems are tuned down increasingly if months or years pass without the body encountering the entity.

Among the approved vaccines against SARS-CoV2, most of the them require two doses (two shots) for the recipient to acquire the initial immunization protection, at least based on the analysis of data obtained during clinical trials of each vaccine. One of the approved vaccines, the Johnson and Johnson (Janssen) vaccine, requires just one shot for “full” immunity. However, the number of shots needed and the time spacing between them were worked out initially based merely on the goal of getting the greatest number of people immunized as quickly as possible, which is a logical policy. There is now much discussion surrounding the notion that, subsequent to one’s receiving the second dose (or the first dose in the case of Janssen), immunity wanes over time, and a related notion that administration of an additional dose —meaning a 3rd dose, if the person has received a two-dose regiment vaccine, such as the Pfizer/BioNTech, Moderna, or Oxford/AstraZeneca—  will compensate for the decreased immunity. These two connected notions may be true, but they are founded on studies and data that have yet to be confirmed, and it is all part of a spectrum of ideas of varying certainty, so let’s dig deeper.

One idea that the data do come together to support clearly is that people with weakened immune systems, such as organ transplant recipients cancer patients who have received certain types of treatments, often experience a blunted response to the normal vaccination treatment (for example the two-shot Pfizer/BioNtech) and can produced better immunity after an additional shot. It is also increasingly clear from the data that people who have obtained some natural immunity, due to previous COVID-19 or previous asymptomatic infection with SARS-CoV2 produce much better immunity if vaccinated, even after just one dose. Also, receiving an mRNA vaccine (Pfizer/BioNTech, Moderna) may possibly improve immunity in people who have received other COVID-19 vaccines, such as the Chinese Sinovac/CoronaVac.

When it comes to a booster shot for healthy people who have been fully vaccinated against SARS-CoV2, however, the benefits are still mostly hypothetical for a few reasons. Papers that were posted in pre-print (not yet peer-reviewed) form in late August, presenting Israeli data pointing to a benefit of giving everybody a third shot of the Pfizer/BioNTech vaccine were later critiqued for improper statistical analysis, for instance. Also, it is important to keep in mind that there is a great deal of debate in the scientific community about how to determine the strength of immunity. In most studies, the data that are analyzed come from measuring antibody levels, which give a hint about the person’s immunity —by 6-8 months after full vaccination, the antibody levels have decreased— but antibody levels do not tell the entire story of immunity, which also depends greatly on what is happening with T-lymphocytes. On top of this, the methods for measuring antibody levels are inconsistent between various laboratories.

This means that the idea that receiving a booster shot as early as 6 months after your second shot of a Pfizer/BioNTech, Moderna, or AstraZeneca vaccine, or 6 months after your single shot of Janssen, is beneficial comes down to an educated guess. I reason that an extra shot at that point will probably be helpful, but this raises the issue of equity.

Given the uncertainty at this point, the most reasonable argument that has been made against administration of a booster shot in healthy people is that billions of people spread through many countries still have not received a first dose. The problem with this reasoning, however, is that holding off from given people third shots of an mRNA vaccine generally would not help those doses reach people who would not otherwise be vaccinated. The situation is analogous to what you may remember your parents telling you in early childhood —or late childhood— about the need to finish your food, because there are children staring in Africa, or in India. Or maybe you are saying this to your own children now, but either way the response is typically “So send it to them!”. The food could not be sent, so it was thrown in the trash. It can be argued that there is a benefit to Israel giving three doses on a massive scale, effectively carrying out a nation-wide clinical trial, producing data, which themselves can be greatly helpful to the world. At the same time, a large country like the United States needs to maintain enough of a supply to give everyone who wants it a first and second dose, where the low temperature storage and transportation requirement for the mRNA vaccines is also a factor for many parts of the world. Putting all of this together, there actually is a “use it or lose it” scenario in many cases. Thus, when offered a third vaccine dose —which will probably be very soon in my case— I will be accepting it, knowing that the dose is indeed likely to be trashed if not put into my arm. Very likely, you are in the same situation, in which you may as well get that booster shot, which, after enough data are analyzed, may indeed turn out to boost your immunity in a meaningful way.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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