A program director emails an infectious diseases faculty member to ask if a SARS-CoV-2 booster is really necessary for their residents, since they are young, have already received 2 prior doses of an mRNA vaccine, and some recent variants have tended to cause milder disease. The program director raises the concern that “the risk of vaccination may outweigh the benefit.”

SARS-CoV-2 boosters were implemented to mitigate the waning effectiveness of vaccines against symptomatic COVID-19 infection.1  By February 13, 2022, 64.2% of the US population had completed the initial COVID-19 vaccination protocol, but only 27.5% had received a vaccine booster.2  Boosters decrease the risk of symptomatic infection and dramatically reduce the rate of hospitalizations in all age groups.3  The reduction in hospitalizations is more evident in those 65 and older, but those in the 18- to 49-year-old age group also benefit. For the week ending February 26, 2022, there were 10.8 hospitalizations per 100 000 boosted individuals 65 years and older vs 26 per 100 000 fully vaccinated, non-boosted individuals 65 years and older. In the 18-49 age group, there were 1.4 hospitalizations per 100 000 boosted individuals compared to 2.1 per 100 000 fully vaccinated, non-boosted individuals.4  Boosting people in the younger age group prevents 0.7 hospitalizations per 100 000 individuals. Is boosting worth it for a young, healthy person?

The short answer is yes.

Some recent data from Portugal can help put this into context. The authors examined predictors of hospitalization for COVID-19 in December 2021 in patients with the Omicron versus Delta variants. As with other studies, the risk of hospitalization with the Omicron variant was considerably lower (hazard ratio 0.25) than for Delta. Even after adjusting for virus strain, age, gender, and prior infection, vaccination that included a booster was estimated to reduce the risk of hospitalization by 93% over no vaccination, versus an 84% reduction for 2 vaccine doses without a booster.5  Booster vaccination has been relatively safe, with no increased adverse reactions to booster doses of mRNA vaccines versus second doses.6 

So, let's do some math. Based on COVID-NET data,4  the overall rate of hospitalization for individuals between 18 and 49 years old for the week ending on January 8, 2022—during the Omicron peak—was 30.6 per 100 000 or 306 per million fully vaccinated (not boosted) individuals, or 0.0306%. This was almost 20 times the highest hospitalization rate for the same age group during the Delta surge—1.7 per 100 000 fully vaccinated individuals. For the week ending on February 26, 2022, corresponding to the end of the Omicron surge, the rate of hospitalization for the same age group was 2.1 per 100 000 fully vaccinated individuals or 21 per million or 0.0021% (Table 1). The number needed to treat (or to boost) to prevent a hospitalization during the Omicron peak was 4255, and it increased to 200 000 by the end of the wave (Table 2).

Table 1

Comparison of Risk of Hospitalization From COVID-19 Versus Risk of Myocarditis

Comparison of Risk of Hospitalization From COVID-19 Versus Risk of Myocarditis
Comparison of Risk of Hospitalization From COVID-19 Versus Risk of Myocarditis
Table 2

Number Needed to Treat to Prevent 1 Hospitalization Due to COVID-19

Number Needed to Treat to Prevent 1 Hospitalization Due to COVID-19
Number Needed to Treat to Prevent 1 Hospitalization Due to COVID-19

Compare this with the risk of a booster-related adverse event. A recent study from the United Kingdom explored the association between vaccination doses and myocarditis.7  No cases of myocarditis were observed after a third dose of the AstraZeneca or Moderna vaccines, possibly due to the relatively smaller number of such individuals in the case series. An additional 2 cases of myocarditis per million vaccinated people from a third dose of the Pfizer-BioNTech vaccine were estimated. In other words, the number needed to harm is 500 000. To account for underreporting and other potential serious adverse events, let's inflate the risk of a serious adverse event due to a booster from 2 in a million cases to 10 in a million, or 0.001%. Even with this adjustment, the risk of a serious adverse event such as myocarditis in a young person with no history of a prior severe adverse event receiving a booster is a small fraction of the risk of hospitalization for COVID-19 during a surge. Even if we drop the hospitalization risk by a log (or by a factor of 10) during surge periods, the benefit of boosting outweighs the risk.

The benefit of boosting younger individuals, such as graduate medical education (GME) residents and fellows, may not be limited to themselves but extends to their families. A Danish study showed that the secondary attack rate, or number of secondary cases, in houses with confirmed cases of COVID-19 was 10% higher in households with a case of the Omicron variant compared to Delta.8  However, boosted individuals were less susceptible to infection by the Omicron variant compared to fully vaccinated non-boosted individuals (OR 0.54, 95% CI 0.40-0.71), and less likely to transmit the infection or have secondary cases in their households compared to fully vaccinated non-boosted individuals (OR 0.72, 95% CI 0.56-0.92).8  This is especially important for households with children who cannot yet be vaccinated.

At the beginning of the pandemic, when vaccines were not available, residents in an internal medicine program in New York City missed a total of 875 workdays after becoming ill with a COVID-19-like illness.9  That is 2.4 calendar years. A reduction in missed workdays is of great significance, as trainee absences are disruptive to patient care, education, and the function of training programs. Training suffers when rotations are disrupted by the need to provide short-term coverage on other services, and such disruption may lead to longer-term impacts on achieving program-specific competency-based milestones necessary for promotion and readiness for unsupervised practice. Trainee absences from illness, isolation, and quarantine disrupt the learning for residents who test positive for COVID-19 or who must quarantine due to an exposure. The learning of their fellow residents is also disrupted if they are pulled to provide clinical coverage and not able to participate in their originally scheduled clinical experience. The incidence of symptomatic and asymptomatic SARS-CoV-2 infection is lower in vaccinated health care workers, which reduces both transmission and days of sick leave.10-12 

The COVID-19 pandemic has disrupted GME through the cancellation of many important educational opportunities through ambulatory care and elective procedures, as well as the loss of in-person conferences that often served to network with peers and mentors.13,14  Furthermore, to accommodate COVID-19 surges, many academic centers reassigned residents and subspecialty fellows to areas outside of their subspecialty training.15  Even though boosting has a very small effect on SARS-CoV-2 transmission, it reduces severity of disease and thereby disruptions to medical training. It is important to recognize that this analysis may change with future boosters and variants. But with all the available evidence, is boosting medical residents and fellows even a question?

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