World Health Organization (WHO) chief scientist Soumya Swaminathan said Monday that herd immunity to coronavirus would not be achieved in 2021, despite the growing availability of vaccines.

世界卫生组织的首席科学家苏米娅·斯瓦米纳坦周一表示，即使疫苗产量不断增加，也不可能在2021年实现对新冠病毒的群体免疫。

Mitigating factors to herd immunity include limited access to vaccines in developing countries, skepticism over vaccination, and the potential for virus mutations, according to health experts.

A growing number of countries around the world, including the United States, the United Kingdom, Singapore, Germany and other European Union countries, are in the first stages of mass-vaccination campaigns.

Herd immunity occurs when enough people in a population have immunity to an infection so that it prevents the disease from spreading.

"We are not going to achieve any levels of population immunity or herd immunity in 2021," Swaminathan told a briefing, while emphasizing that measures like physical distancing, hand washing and mask wearing continue to be necessary in containing COVID's spread for the rest of the year.

However, Swaminathan commended the "incredible progress" made by vaccine researchers to develop several safe and effective vaccines at unprecedented speed. Countries are currently administering vaccines developed by BioNTech-Pfizer, Oxford University/AstraZeneca and Moderna.

The WHO top scientist called on people to be "a little patient," pointing out that the rollout of vaccines "does take time," as the scale of dose production is in the billions.

"The vaccines are going to come," she said. "They are going to go to all countries ... but meanwhile we mustn't forget that there are measures that work," she added, referring to hygiene and social distancing.