Everyone in the United States who got a COVID-19 vaccine will need a booster shot to keep protection from fading, the Biden administration said today. Vaccinated Americans will be offered boosters eight months after their initial shots. Plans are that the first round will be offered in September and will go to nursing home residents, healthcare workers, and others vaccinated early.

“Current protection against severe disease, hospitalization, and death could diminish in the months ahead, especially among those who are at higher risk or were vaccinated during the earlier phases of the vaccination rollout,” federal health officials said in a joint statement.

The current proposal only includes the Pfizer / BioNTech and Moderna vaccines. Officials say they’re expecting additional data to guide decision-making around boosters for the Johnson & Johnson vaccine in the coming weeks.

It’s a reversal from early July, when the Centers for Disease Control and Prevention (CDC) and Food and Drug Administration (FDA) released a joint statement saying that most people do not need booster shots. It’s also likely to be controversial from a global equity perspective — the majority of people in low-income countries haven’t received first doses yet.

The fast-spreading delta variant changed the equation. The administration is concerned that protection against the coronavirus could fade, either because of the passage of time or the variant, officials told The Washington Post. Preliminary data out of Israel, published as preprints that have not undergone peer review and through releases from the Ministry of Health, suggests the vaccine became less effective at preventing COVID-19 infections and symptomatic cases in the face of the country’s delta surge. Data released from the Ministry of Health also suggested efficacy against severe cases of COVID-19 may be eroding for older adults. Israel is offering booster doses to people 60 years of age and older.

Data from the United States also shows vaccine effectiveness against coronavirus infections declining over time, CDC Director Rochelle Walensky said during a press briefing. The shots are also less effective against infections from the delta variant, CDC data shows: effectiveness declined from 92 percent before the delta variant to 64 percent with the delta variant in one US group, Walensky said. Protection against severe cases of COVID-19, hospitalization, and death remain high.

Still, there’s no data yet showing if the booster would offer additional protection against delta. A third dose generates higher levels of antibodies against the virus, but it’s not clear if or how much that would translate to additional protection against COVID-19. Pfizer has a clinical trial testing that question underway.

Even if boosters can improve protection for fully vaccinated people, that wouldn’t do as much to blunt COVID-19 surges as would vaccinating more people in the US, Boston University epidemiologists Eleanor Murray and Ruby Barnard-Mayers wrote in The Washington Post. Only 62 percent of US adults are fully vaccinated. There are still no COVID-19 vaccines authorized for kids under 12.

Although the Biden administration announced the plan today, booster shots can’t roll out without clearance from the FDA and recommendation from the CDC. There are no booster shots currently authorized by the FDA, though once the agency fully approves the vaccines (which it’s expected to do by early September), physicians would have more flexibility to distribute additional doses. Pfizer submitted initial data on booster doses to the FDA this week.

The CDC recommended last week that people with compromised immune systems get third doses of either the Pfizer / BioNTech or Moderna vaccine, as many don’t produce enough antibodies after the regular series. That third dose isn’t considered a booster — it’s an expanded initial vaccine regimen.

Earlier this month, the World Health Organization (WHO) called for a moratorium on COVID-19 vaccine boosters until the end of September so that more vaccine supply could make it to low-income countries. There are huge gaps in vaccine access between high and low-income countries — only around 1 percent of people in low-income countries have received even one dose of a COVID-19 vaccine.

“This is a global pandemic and we need to think about global solutions,” Maria Van Kerkhove, COVID-19 technical lead at the WHO, told CNN. “All of the world’s most vulnerable, and those who are most at-risk — health workers — need to receive their first and second doses before a large proportion of the population or all of the population in some countries receive that third dose.”