The Delta variant of the coronavirus has caused serious concern because laboratory tests have shown that it is more infectious and resistant to vaccines than other forms of COVID-19.

However, there is evidence that the available jab is still effective against it after two doses.

Here is what you need to know:

A British study published in the medical journal The Lancet in early June investigated the levels of neutralizing antibodies produced by vaccinated people who were exposed to Delta, Alpha (first discovered in the UK) and Beta (first discovered in South Africa) variants .

It found that in the presence of the Delta variant, people who received two doses of Pfizer’s BioNTech vaccine had six times lower antibody levels than the original COVID-19 strain on which the vaccine was based.

Alpha and Beta variants also caused a lower response, with Alpha’s antibodies being reduced by 2.6 times and Beta’s antibodies by 4.9 times.

A French study by the Pasteur Institute concluded that neutralizing antibodies produced by Pfizer-BioNTech vaccination are three to six times more effective on Delta variants than on Alpha variants.

So is the vaccine still effective?

Although they represent an important marker, the antibody levels measured in the laboratory are not sufficient to determine the efficacy of the vaccine. In particular, they did not consider the second immune response in the form of killer T cells-it attacks already infected cells, rather than the virus itself.

Therefore, real-world observations are critical to measuring the effectiveness of vaccines-and the preliminary results are gratifying.

According to data released by the Department of Public Health on Monday, for Delta variants and Alpha variants, Pfizer-BioNTech and AstraZeneca vaccination are equally effective in preventing hospitalization.

According to a study involving 14,000 people, two doses of Pfizer BioNTech injections prevented 96% of hospitalizations due to Delta mutations, while the AstraZeneca vaccine prevented 92%.

Previous data released by British health authorities at the end of May reached similar conclusions for less serious forms of the disease.

The Pfizer-BioNTech vaccine is 88% effective for symptomatic COVID-19 caused by the Delta variant and 93% for the cases caused by the Alpha variant two weeks after the second injection.

AstraZeneca has 60% of cases caused by Delta variants and 66% of Alpha cases.

The Scottish authorities published similar figures in The Lancet on Monday.

At the same time, the team behind the Sputnik V jab stated on Twitter on Tuesday that their vaccine “is more resistant to the Delta variant… than any other vaccine that has published results for this strain so far.” They did not publish the results, but stated that the research of the Gamaleya Center, a Russian research institution, has been submitted to an international peer-reviewed journal for publication.

Is one shot enough?

Among the available vaccines, only Johnson & Johnson’s products require one dose—not two doses—to be effective. So far, there is not enough data to determine how it will fight against the Delta variant.

As for other jabs, laboratory and real-world tests have concluded that a single dose of any vaccine can only provide limited protection against the Delta variant.

“After a single dose of Pfizer-BioNTech, 79% of people had a quantifiable neutralizing antibody response to the original strain, but for B.1.617.2, this proportion dropped to…32% [Delta],” said the June laboratory study.

The Pasteur Institute found that a single dose of AstraZeneca had “almost no effect” on the Delta variant.

Data from the British government confirms the real-world trend: the two vaccines are effective at 33% for symptomatic cases caused by Delta after three weeks of the first dose, while the effective rate for Alpha variants is about 50% .

In the United Kingdom-where the Delta variant currently accounts for 96% of new cases-these findings prompted the government on Monday to shorten the interval between two vaccinations for people over the age of 40 from 12 to 8 weeks.

In France, the waiting time for the second dose of Pfizer-BioNTech and Moderna vaccines has been reduced from five weeks to three weeks.

However, Pfizer-BioNTech injections do provide very high (94%) protection against hospitalization due to the Delta variant after one dose.

So what is the best strategy to combat Delta’s strain?

Scientists agree that the best defense against Delta variants is to receive a complete two-dose vaccine.

Top French scientist Jean-François Del Flessi said that creating a “vaccinated population” will help prevent the Delta variant from spreading throughout the population.

A study in the United States on June 10 pointed out the importance of vaccination to prevent the list of variants from growing.

It said: “Increasing the proportion of the population receiving current safe and effective authorized vaccines remains a key strategy to minimize the emergence of new variants and end the COVID-19 pandemic.”

Antoine Flahault, director of the Institute of Global Health at the University of Geneva, insists that it is still vital to observe social distancing, share infection information and comply with restrictions when necessary to “keep the spread of the virus low.”

He said that the more the virus spreads, the greater the chance it will mutate and produce new mutations.