United States’ top virologist Anthony Fauci on Friday reiterated that the Delta variant of the coronavirus infection was more lethal and warned against the possibility of an increase in infections wherever the strain was present, NDTV reported.

“The problem is that the Delta variant is one that spreads much more readily and much more efficiently,” Fauci said in an interview to the news channel. “So, any country that has the [B.1.]617 Delta variant should be concerned that there will be a surge of infections.”

Noting that 6% of the infections in the United States were caused due to the Delta variant, Fauci added that the strain can become “dominant very, very quickly” when it spreads among the non-vaccinated population.

“That’s exactly what is going on in the UK [United Kingdom], that the Delta variant is taking over...It is close to 90% dominant right now. In the United States it’s just 6%,” Fauci told NDTV.

His comments came on a day when the United Kingdom government said that the Delta variant, which was first detected in India, is 60% more transmissible in households than the Alpha variant, first detected in the country’s Kent county. A report released by the Britain’s health body Public Health England also showed that the strain accounted for 96% of new Covid-19 cases detected in the country over the last week.

When asked about the possibility of a third wave of the pandemic in India, Fauci said that the prospect was linked to vaccination coverage. “If you have a country in which a relatively small proportion of the population is vaccinated, you are vulnerable to successive waves...We have seen that in the United States,” he told NDTV.

He added that while the vaccines, which are currently in use, show a slight moderation in efficacy against the Delta variant, but there is not much to “worry about it”.

Fauci’s comment came days after a research published in the medical journal Lancet had shown that the coronavirus vaccine developed by pharmaceutical company Pfizer is likely to produce 5.8 times lower levels of antibodies against the Delta variant.

On the ideal interval between the two doses of Covid-19 vaccines, Fauci said that in case of the two mRNA vaccines in use in the United States, the recommended gap was three weeks for the Pfizer shot and four weeks for the Moderna jab.

“One of the problems with extending duration is that you become vulnerable to the variants and we have seen that in the UK...So we recommend staying on schedule,” Fauci told NDTV. He, however, added that it could be necessary to extend the interval in case the supply of vaccines was limited.

The Pfizer and Moderna vaccines that Fauci mentioned are currently not in use in India. None of the vaccines approved in India so far are being administered in the United States.

Days after the Indian government had extended the gap between two doses of the Covishield vaccine, Fauci had backed the move, referring to it as a “reasonable approach” to take when faced with a shortage of doses.

“It is very unlikely that it would have a negative effect on the efficacy of the vaccine,” he had said.