Despite widespread vaccination campaigns, herd immunity to coronavirus will not be achieved this year the WHO's top scientist has said. Until then, preventative measures like masks will be necessary.

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. 

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. 

Making progress, but vaccines 'take time' 

"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.

In the US, which currently has the world's highest daily case numbers, officials said Monday over 25,400,000 vaccine doses have so far been distributed, with nearly 9,000,000 doses having been administered.

In Germany, more than 600,000 people have so far been vaccinated against COVID, according the Robert Koch Institute for public health. 

Herd immunity must be global 

"We won't get back to normal quickly," Dale Fisher, chairman of the WHO's Outbreak Alert and Response Network, told a conference hosted by Reuters news agency.

"We know we need to get to herd immunity and we need that in a majority of countries, so we are not going to see that in 2021," Fisher said.

"There might be some countries that might achieve it but even then that will not create 'normal' especially in terms of border controls," he added.