It’s been close to 6 months since the initial rollout of the fall (bivalent) booster. A lot of people are wondering: Do I need a spring booster?
The answer hinges on more questions: What is the purpose of vaccines? Does that purpose change depending on age or health status?
The Purpose of the COVID Vaccines
Last month, the FDA and CDC made it clearopens in a new tab or window that the primary purpose of vaccines is to prevent severe disease and death. Decreases in infection and transmission are a bonus at this point, and unfortunately, protection against infection is only temporary.
This makes sense for younger and healthier people. They are staying out of the hospital from COVID-19 for three main reasons:
- Hybrid immunity. Younger people are more likely to have been infected. People with both vaccination and infection history have protection that lasts longer.
- Less likely to have comorbidities. Their immune systems are less taxed.
- Robust immune memories, particularly T-cells. Their thymuses (the organs that give rise to T cells) haven’t gradually degraded into useless blobs of fat, yet.
This means that even if antibodies are waning after 5-6 months, this is okay because protection against severe disease isn’t waning yet.
The story is different for immunocompromised and other very high-risk groups, like older Americans with comorbidities. The purpose of the vaccines for this group should also be to prevent severe disease and death. However, one could argue that in order to do that, we also need to prevent illness.
There’s one big reason for this: SARS-CoV-2 infection can exacerbate potentially fatal underlying illnesses, like heart failure or diabetes. Protection against viruses and underlying illnesses relies on antibodies to act quickly before the immune system is pulled in multiple directions. If it is pulled in multiple directions, it can lead to hospitalization and death.
The Immunocompromised
Of the COVID-19 hospitalizations today, 25% are among the immune-compromised. (Immune-compromised make up 3% of the general population). There are really two subgroups to think about:
- Non-responders to vaccines. At this point, this is a very small group of people, like organ transplant patients. Some people who did not respond to 2 or 3 doses eventually did respond to 4 or 5 doses. For the remaining non-responders, one could argue that there’s no point in boosting them, but the downsides of trying seem low.
- Protection wanes quickly. The majority of immunocompromised people belong in this second group. The vaccine works, but just not as well and not as long. For them, vaccine effectiveness against hospitalization with the fourth dose peaks at 51% at 0-2 months, then drops to 28% by 2-4 months. (The bivalent booster may increase protection and duration, but we don’t know yet.)
- There are few downsides to boosting this group every 6 months. It’s actually possible that the immune-compromised are somewhat protected against imprintingopens in a new tab or window by virtue of their sluggish immune systems.
- Older Americans With Comorbidities
- Those 65 years and older are contributing more and moreopens in a new tab or window to the proportion of deaths over time. Among adults hospitalized for COVID-19, 96% had at least one underlying condition.
- This is because 2 of the 3opens in a new tab or window defense walls have more holes than those of younger people. Comorbidities also increase with age, which means the immune response in general is a lot more taxed.
- So this is another group in whom we want to prevent infection in order to prevent severe disease.
- The latest dataopens in a new tab or window from the last ACIP meeting shows waning protection against infection among this group after 4-5 months.
- The good news is that we clearly see that the risk of severe disease even in the very elderly dramatically declinesopens in a new tab or window with vaccination. In fact, very few people are in the hospital today who are up-to-date on vaccines. However, will this change with time? How much each booster helps (or does not help) incrementally is something that we really don’t have a good grip on prospectively.