Get a second booster?
In these newsletters I've promoted COVID-19 vaccines and boosters, because the data show that they help protect you (and those in your vicinity).
Now that a second booster may be an option, I want to be a cheerleader for it, but.... the data aren't as persuasive. It pains me a little to say that.
In this newsletter I won't take sides. I won't say that you should or shouldn't get a second booster when it becomes available. I just want to share some stats, put them in context, and let you decide for yourself.
Background
The FDA is reviewing data now on the use of current vaccines as second boosters; emergency use authorization is likely by fall. Meanwhile, Pfizer and Moderna are testing second boosters that have been modified to be omicron-specific. Thus, in the near future, the FDA could authorize (a) current vaccines for use as second boosters, (b) new, omicron-specific second boosters, or (c) both.
(The differences between "primary doses", "additional doses", "boosters", " and "fourth shots" are explained in the Appendix.)
What do the statistics tell us?
Here are the two most relevant findings from studies conducted this year:
(a) The effectiveness of the first COVID-19 booster declines over time.
(b) A second COVID-19 booster increases key antibody levels.
These findings seem to justify second boosters, but the data seem equivocal in each case. Below I discuss each finding in turn.
(a) Decline in first booster effectiveness
Studies show that vaccine effectiveness increases shortly after the first booster and then diminishes over time. In the U.S., the largest of these studies found that four months after boosting, protection against hospitalizations declined from 91% to 78%.
I trust this study. The sample was large (93,408 hospitalizations across 10 states), key variables were controlled for (age, health, etc.), the main variables were relatively unambiguous (vaccine status and hospitalizations), and the results echo those of smaller studies. All the same, the findings don't overwhelmingly call for a second booster.
A critical point is that in this study, effectiveness was defined in terms of hospitalizations rather than infection rates, and hospitalization is an uncommon outcome. Consider that 78% statistic. It tells us that if you're vaccinated and boosted, then four months after your booster, you're 78% less likely than an unvaccinated person to be hospitalized for COVID-19. (Of course, you're less likely than an unvaccinated person to be infected in the first place.)
Let’s put that 78% figure in context. CDC data show that for everyone (vaccinated, vaccinated-and-boosted, unvaccinated), hospitalizations were over 10 times higher in January of this year than in January 2021. That's a big jump, and it makes headlines, but it's a relative increase. The absolute rates are still low. For instance, in January of this year, about 10 out of 100,000 vaccinated-and-boosted adults were hospitalized each week for a breakthrough infection. (Data for February aren't available yet.)
This stat doesn't mean that if you're vaccinated and boosted, your chances of being hospitalized for a COVID-19 infection in any given week are 10 in 100,000. Your actual chances depend on your age, your health, your city, your behavior, etc., and so the individual risk value can’t be precisely calculated. But consider this: If there are 10 unique breakthrough hospitalizations per 100,000 people each week for the next year, the breakthrough rate will be 10 x 52 = 520 out of 100,000, which is 1.04 out of every 200 vaccinated-and-boosted people.
In short, if breakthrough hospitalizations continue at their current rate, then by February of next year, roughly 1 in 200 vaccinated-and-boosted Americans will have been hospitalized during the year for a COVID-19 infection. That adds up to a large number of people, because our population is large, but your individual chances remain low. As I said, "low" can't be defined precisely, but four months after your booster, they'll be 78% lower than they are for unvaccinated people.
Since that 78% figure is a decline from 91% shortly after boosting, we might ask: Will booster effectiveness continue to decline beyond the four-month mark? Maybe, maybe not. Studies on other vaccines reveal substantial variability in how much their effectiveness changes over time. At one end of the spectrum, the annual flu shot loses about 10% of its effectiveness each month after you receive it; on the other hand, the MMR vaccine gives you lifelong protection against measles and rubella. In between these extremes is the primary series of tetanus shots, which maintains minimally protective levels up to about 10 years (or 30 years, according to a new study). COVID-19 vaccines probably fall somewhere in the middle too, and so for now, we may need to just live with Anthony Fauci's appropriately vague remark that 78% effectiveness is "still a good protective area".
(b) Benefits of a second booster
Preliminary data on second boosters are promising. For example, among 274 Israeli medical workers who received a second booster (either Pfizer or Moderna), antibodies increased to roughly the same levels attained after the first booster. This seems like clear evidence that you should get a second booster, right?
Well, sort of.
For vaccines whose immunological benefits diminish over time, boosters will increase antibody levels. However, boosters aren't offered every time antibody levels decline, because, for some vaccines, boosting would be needed so often that it wouldn't be an affordable or sustainable strategy (much less palatable to the general public). There would also be a risk of undermining immune system functioning.
In short, the goal is a "sweet spot" where vaccines are administered often enough to protect public health, but not so often that they become harmful or impractical. Some loss of effectiveness is expected, but there's no objective cut-off point.
To illustrate what I mean here, consider influenza vaccine guidelines. The CDC and other authorities recommend one flu shot per year, in autumn, before case rates begin to spike. But no particular month is consistently optimal, because flu spreads during the winter at different rates depending on the year and the region. Likewise, there's nothing special about the 12-month mark, because the effectiveness of the flu vaccine decreases about 10% per month. The CDC's guidelines represent their best attempt at a strategy that protects people while being affordable, sustainable, and likely to maximize public compliance. Not all experts agree with those guidelines.
The same kind of strategy will be needed for second COVID-19 boosters, and we won’t find consensus there either. Debates are already underway about how much decline in effectiveness after the first booster would be tolerable and render a second booster unnecessary. If that 78% effectiveness against hospitalization holds for considerably longer than four months, then some experts, like Anthony Fauci, won't end up recommending a second booster after all.
Expect future discussion of this topic to be contentious, partly because vaccine-related topics are deeply politicized, and partly because agencies like the CDC continue to struggle with messaging. Meanwhile, new variants may continue to emerge. (Fortunately, preliminary data on BA.2 suggest that although it may be more contagious than what we call omicron, it doesn't lead to more hospitalizations.)
In sum, the fact that boosters improve immune system functioning doesn't mean that a second COVID-19 booster will automatically be a good idea.
Final thoughts
Unless you're immunocompromised, I don’t think you should stress about whether or not to get a second booster. Reasonable arguments can be made both for and against this option. If you're fully vaccinated and boosted already, and you still mask and/or distance when needed, then your chances of winding up in the hospital from a COVID-19 infection are already extremely low, and would be lowered slightly by another booster.
I'll include updates in future newsletters. In the meantime, stay safe, and have some fun!
Appendix: Terminological notes
A "primary series" (also known as "primary dose", "full course", or "standard regimen") is the vaccine treatment deemed necessary to achieve full effectiveness. This is two Pfizer or Moderna vaccines, or one from Janssen.
A "first booster" is the vaccine given after a primary series. A "second booster" would be the vaccine given after the first booster. So, if you had Pfizer or Moderna (or one of each) as your primary series, the first booster would be your third shot. If you had Janssen as your primary series, the first booster would be your second shot.
An "additional dose" is not the same as a booster. Rather, it's an additional vaccination, following the primary series, that immunocompromised people receive in the hopes that they'll attain the level of protection that people with normal immune system functioning get from a primary series.
Finally, you sometimes see the term "fourth vaccine" (or "fourth shot"). Usually it refers to a second booster (e.g., in studies where participants have already had a Pfizer or Moderna primary series, followed by a first booster). However, it may refer to a first booster in discussions of immunocompromised people who received a primary series and an additional dose.