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No Need to Wait for Herd Immunity

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eye on the news

No Need to Wait for Herd Immunity

Even limited deployment of a Covid vaccine could have a major impact. September 30, 2020
Covid-19

As we get closer to full approval of one or more of the promising candidates for a Covid vaccine, it’s becoming clear that we will not quickly have an adequate supply to vaccinate the entire adult U.S. population, and that many will forego this first round of vaccination. As such, it’s unlikely that an emergency vaccine will allow us to stop the spread of infection through herd immunity.

An effective vaccine can still fit into a broader transmission-control strategy, however. A few months back, I wrote that it’s “reasonable to conclude that we may see continued outbreaks for more than one to two years,” and that the U.S. needs to learn how to coexist with the virus. Even a moderately effective vaccine of limited availability and acceptance can significantly improve our ability to do this.

In the next six to eight weeks, the FDA is likely to review an interim analysis of the results of one or more of the Phase 3 trials underway. Many assume that this review will result in FDA approval of vaccine for emergency use; full approval will most likely come in the first quarter of 2021, after six months of follow up.

If emergency use of the vaccine is granted, the highest risk and most vulnerable individuals will be among the first vaccinated. While it’s not yet clear exactly who will fall into these categories, they will likely include health-care personnel, first-line emergency responders, those with chronic disease, and the elderly. (With luck, they will also include those living in communities hit hardest by the virus.) But even if only elderly people receive the first round of vaccinations, it will significantly change the risk-benefit equation for controlling the spread of Covid.

Early in the pandemic, the U.S. failed to incorporate geography’s role as a determinant of disease into its control strategies. Initially, Covid hit hardest in West Coast and northeastern cities, and especially in disadvantaged neighborhoods within them. Drastic interventions in these areas were essential to saving lives and preventing the health-care system from being overwhelmed. However, applying the same interventions to unaffected geographies imposed massive costs for a more limited benefit.

As we consider how to deploy a vaccine, we must not repeat this mistake. Age, followed by geography, seems to be the best way to consider Covid infection data. In addition, hospitalization—as a measure of severity of illness and strain on health care—is probably a better first-level indicator than number of cases. According to the CDC’s latest report, weekly hospitalization for the under-50 cohort was less than one per 100,000; at its peak, the rate for this group was between one and two per 100,000. In contrast, the most recent weekly rate for those 65 years and older was five per 100,000, and 35 per 100,000 at its peak.

To put these hospitalization figures into context, we need to look at Covid-related deaths and cases. While we have seen a significant decline in weekly deaths since the peak last spring and early summer, most deaths continue to be among those 65 years and older. As of late August, there were fewer than 20 Covid-related deaths per week for the under-24 segment, and more than 3,500 per week for those 65 years and older. The age differences persist even though, according to the CDC, the median age of confirmed Covid-19 cases decreased from 46 years old in May to 38 in August.

Data continue to confirm the belief that the main risk surrounding an increase in the number of Covid cases concerns medically vulnerable individuals. Mandates for masks and social distancing are justifiable only in order to protect those most likely to be hospitalized and die. If Covid has a limited impact on vulnerable populations, then there would be no need for government officials to take decisions about mitigating risk out of individuals’ hands.

If we can distribute an emergency-approved vaccine to the elderly and those with chronic health problems, then the cost-benefit ratio tips greatly in favor of lifting restrictions on in-person schooling, indoor seating at restaurants, and venues like theaters, sports arenas, and museums—even if we still see some spikes in Covid cases. An emergency vaccine, deployed intelligently, can thus bring us back to normal life much sooner than a strategy of waiting to achieve herd immunity.

Photo: MarianVejcik/iStock

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