Eric J. Topol is a professor of molecular medicine at Scripps Research. Michael T. Osterholm is Regents Professor and director of the Center for Infectious Disease Research and Policy at the University of Minnesota.

Even though the United States is experiencing a new surge of covid-19, the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices recommended last week that all adults be made eligible for booster shots but only urged shots for people older than 50.

That was a big mistake. It should have urged all adults to get them.

Public health officials have always expected that mRNA coronavirus vaccines (Moderna and Pfizer/BioNTech) to be a three-shot regimen. The only question was when the third shot would be necessary. Originally, the hope was that it would be after one or two years. It turns out, it is necessary at about six months.

More than 10 large reports have shown that the reduced protection from infections, including symptomatic infections, across all age groups, wanes from 90 to 95 percent at two months down to about 60 percent for Pfizer and 70 percent for Moderna after five to six months. There is further substantial waning after six months.

The good news is that a booster dose can restore that initial efficacy, as data makes abundantly clear. One randomized trial of Pfizer’s vaccine involving more than 10,000 participants — half receiving a third shot and the other half receiving a placebo booster — showed a remarkably high 95-percent efficacy. In that trial, people aged 18 to 55 benefited just as much as those older than 55. There were no safety issues raised, such as myocarditis.

It is important to underscore that for all coronavirus vaccine trials, symptomatic infection has been the primary endpoint, and has tracked well with hospitalizations and deaths. Large, randomized trials are rightly considered the gold standard form of evidence. There are no other randomized trials of booster shots underway.

Israel offers more evidence of the booster’s benefits. Its largest health system tracked more than 700,000 people who had received a booster shot and found that the third shot had a striking 91 percent effectiveness against symptomatic infection. It also had a 93 percent effectiveness against hospitalization and 81 percent effectiveness against covid-related deaths.

But the CDC’s advisory committee didn’t review this important observational study and many other relevant data sources. If it had, perhaps it would have more forcefully advocated boosters for all adults. Our recommendation is fully consistent with messaging from the White House and President Biden that all vaccinated adults should get boosters.

Its failure to do so has substantial implications. Only 59 percent of the U.S. population is fully vaccinated, meaning the United States ranks below the top 50 most-vaccinated countries. Countries throughout Europe, such as Denmark and Belgium, have vaccination rates of around 75 percent, and even they are experiencing record-setting surges in cases.

Like Britain and Israel, the United States was a first mover with early vaccination campaigns, so it has a much higher proportion of people with waning immunity. Forty percent of Americans (more than 120 million people) were fully vaccinated by June 1 and have diminished protection. Each day in the United States, the number of people with waning immunity greatly exceeds those who are getting newly vaccinated. Accordingly, rather than building our wall of population immunity, the United States is suffering attrition.

It has been estimated that more than 90 percent of Americans need to be fully vaccinated to contain the hyper-contagious delta variant. Not only are we far from that goal, but also we are moving in the wrong direction. While we continue to press ahead to reach unvaccinated Americans, we must concurrently maintain protection for those who have received the shot.

This is especially concerning amid the new surge, which has been labeled a “pandemic of the unvaccinated.” This is misleading; it is critical to recognize the category of “vaccinated but waned.” Multiple studies have shown that fully vaccinated people can spread the delta variant. This is more likely when the vaccine-induced immune response has faded. Since booster shots strongly reduce symptomatic infections, they could help stem the increased spread that we are experiencing.

Israel used booster shots for all adults as its principal — and highly effective — strategy to manage its worst surge of the pandemic. There, the status of “fully vaccinated” is defined as having received three shots. Indeed, the United States has consistently ignored critical lessons from Israel and Europe throughout the pandemic.

By not strongly urging all fully vaccinated adults to get a third shot, the CDC has failed its responsibility to protect the public, fundamentally missing a strategy that would limit the surge in cases — not to mention the toll it will have in terms of long covid-19 and hospitalizations. It has also engendered confusion by not keeping its recommendation simple, suggesting an illusion that there is a sharp age gradient for the benefit of boosters, which is clearly not the case.

Now, as we confront yet another surge, it is not the time to withhold a vital and validated means of boosting our efforts to contain the virus.