The Food and Drug Administration has laid out a road map for what Covid-19 vaccination may look like moving forward.

In a briefing document published Monday, the FDA said the vaccines will probably need an annual update as the virus continues to evolve. The agency would select the Covid strain for the vaccine in the spring so the updated shots could roll out every September in time for a fall vaccination campaign.

Most people would receive one shot to restore their protection against the virus moving forward, according to the briefing document. This would apply to people who have been exposed to the virus’s spike protein at least twice, either through vaccination or infection.

But older adults and people with compromised immune systems may need two doses, according to the proposed vaccination schedule. Young children who have received only one shot previously would also get two doses.