For the first time in more than a year, we’re feeling some hope—or at least cautious optimism—that the pandemic could recede to the background. But experts want us to know that there is still a concern that new mutations of the virus could bring it back, and it might be even stronger. Viruses constantly change to adapt and survive, and variants emerge when a strain has one or more mutations that differ from others.

The Delta variant, also known as B.1.617.2, can spread more easily, according to the CDC. The strain has mutations on the spike protein that make it easier for it to infect human cells. That means people may be more contagious if they contract the virus and more easily spread it to others. It is now the dominant strain in the U.S.

In fact, researchers have said that the Delta variant is about 50% more contagious than the Alpha variant, which was first identified in the U.K., according to The Washington Post. Alpha, also known as B.1.1.7, was already 50% more contagious than the original coronavirus first identified in China in 2019.

The World Health Organisation (WHO) said the Delta variant of COVID-19, which triggered UNILAG shutdown Wednesday is now in 111 countries of the world.

This was up from 104 countries reported on Monday.

WHO Director-General, Dr Tedros Ghebreyesus said the spread of the variant, along with increased social mobility and the inconsistent use of proven public health measures was driving increases in both case numbers and deaths.

He spoke Wednesday in remarks to the 8th meeting of the Emergency Committee on COVID-19, established under International Health Regulations (IHR), a treaty that guides global response to public health risks.

Tedros recalled the sustained decline in COVID-19 cases and deaths in recent months, driven largely by increasing vaccination rates in Europe and North America, but sounded alarms over the fresh reversal of that positive trend.

“Unfortunately…we are now in the early stages of a third wave,” he said.

Last week marked the fourth consecutive week of rising cases of COVID-19 globally, with increases recorded in all but one of WHO’s six regions. Deaths are also rising again, after 10 weeks of steady decline.

“The Delta variant is now in more than 111 countries and we expect it to soon be the dominant COVID-19 strain circulating worldwide, if it isn’t already,” Tedros said.

What is the Delta variant? Here are the insight by Webmd.com:

The Delta variant, also known as B.1.617.2, can spread more easily, according to the U.S. CDC. The strain has mutations on the spike protein that make it easier for it to infect human cells. That means people may be more contagious if they contract the virus and more easily spread it to others. It is now the dominant strain in the U.S.

In fact, researchers have said that the Delta variant is about 50% more contagious than the Alpha variant, which was first identified in the U.K., according to The Washington Post.

Alpha, also known as B.1.1.7, was already 50% more contagious than the original coronavirus first identified in China in 2019.

Public health experts estimate that the average person who gets infected with Delta spreads it to three or four other people, as compared with one or two other people through the original coronavirus strain, according to Yale Medicine.

The Delta variant may also be able to escape protection from vaccines and some COVID-19 treatments, though studies are still ongoing.

What is the Delta Plus variant?

The Delta Plus variant, also known as B.1.617.2.1 or AY.1, is considered a “subvariant” of the Delta version, according to CBS News. It has a mutation that allows the virus to better attack lung cells and potentially escape vaccines.

First identified in India, Delta Plus has now been found in the U.S., U.K., and nearly a dozen other countries. India has labeled it a variant of concern, but the CDC and WHO haven’t.

Where did the Delta variant come from?

The Delta variant was first identified in India in December 2020 and led to major outbreaks in the country. It then spread rapidly and is now reported in 111 countries, according to WHO director-general.

As of early July, Delta has become the dominant form of the coronavirus in the U.S., U.K., Germany, and other countries. In the U.K., for instance, the Delta variant now makes up more than 97% of new COVID-19 cases, according to Public Health England.

What are the symptoms of the Delta variant?

The symptoms are similar to those seen with the original coronavirus strain and other variants, including a persistent cough, headache, fever, and sore throat.

At the same time, COVID-19 patients in the U.K. have reported that some symptoms are slightly different for Delta, according to data from the ZOE COVID Symptom Study. Cough and loss of smell seem to be less common. Headache, sore throat, runny nose, and fever seem to be more common.

Is the Delta variant more deadly?

Scientists are still tracking the data to determine how deadly it is. Based on hospitalizations in the U.K., the Delta variant does seem to be more likely to lead to hospitalization and death, particularly among unvaccinated people, according to a recent study published in The Lancet.

What does the Delta variant mean for the unvaccinated?

People who haven’t been fully vaccinated against COVID-19 are most at risk, Yale Medicine reported. In the U.S., communities with low vaccination rates have seen a jump in cases, particularly in Midwest and Southern states such as Missouri and Arkansas. Outbreaks have also been found in Mountain states, such as Wyoming.

Kids and younger adults who haven’t been vaccinated may be susceptible as well. In the U.K., children and unvaccinated adults under age 50 were 2.5 times more likely to become infected with Delta, according to a recent study published by Imperial College London.

What does the Delta variant mean for the vaccinated?

Scientists are looking at how the Delta variant can cause breakthrough cases, or infections among people who are fully vaccinated. So far, they seem to be rare.

In a preliminary analysis, two doses of the Pfizer or Moderna vaccine appeared to be about 88% effective against disease and 96% effective against hospitalization with the Delta variant, according to Public Health England. The AstraZeneca vaccine, which has not been authorized for use in the U.S., was about 60% effective against disease and 93% effective against hospitalization. Johnson & Johnson has also reported efficacy from its one-shot vaccine against the Delta variant, which researchers estimate to be similar to the AstraZeneca results.

Now vaccine makers are testing booster shots to find out if they can better protect against the Delta variant and other variants that emerge in coming months. Pfizer announced that it will seek FDA authorization for a booster dose in August, according to CNN.