The World Health Organization on Wednesday released an updated plan for COVID-19, laying out three possible scenarios for how the pandemic will evolve this year.

"Based on what we know now, the most likely scenario is that the COVID-19 virus continues to evolve, but the severity of disease it causes reduces over time as immunity increases due to vaccination and infection," Director-General Tedros Adhanom Ghebreyesus said during a briefing.

However, the WHO head cautioned that periodic spikes in cases and deaths may occur as immunity wanes, which may require periodic boosting for vulnerable populations.

Talking about the other two potential scenarios, Tedros said either less severe variants will emerge and boosters or new formulations of vaccines will not be necessary, or a more virulent variant will emerge and protection from prior vaccination or infection will wane rapidly.

The updated Strategic Preparedness, Readiness and Response Plan sets out the strategic adjustments that every country needs to make to address the drivers of SARS-CoV-2 transmission, lessen the impact of COVID, and end the global emergency.

This is the third Strategic Preparedness, Readiness and Response Plan released by WHO and will likely be its last, Tedros said.

The first report was released in February 2020, at the start of the pandemic.