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Do COVID vaccines protect against the delta variant?

Kathrin Wesolowski | Rachel Baig
July 15, 2021

In the United Kingdom, people have died of the delta variant despite being vaccinated. Are existing COVID-19 vaccines still effective? A look at the facts shows: Yes, complete vaccinations still protect against delta.

Masked and unmasked individuals on a crowded Spanish street
Countries around the world have seen sharp rises in the number of people being infected with the delta variantImage: Joan Mateu/AP Photo/picture alliance

In the United Kingdom, at least 259 people have died after contracting the delta variant of COVID-19. Of these, 116 people were fully vaccinated, according to the latest data from Public Health England (PHE), an agency of the UK Ministry of Health. That is why one of the biggest questions being raised on the internet now is: Does a vaccination still protect against the delta variant?

The good news first: Yes, a vaccination still protects you.

Why is there a residual risk despite double vaccination?

None of the vaccinations that have been approved so far provide 100% protection against a coronavirus infection — studies have shown that since their introduction.

Vaccinated people, particularly those with preexisting illnesses, still run the low risk of becoming infected — and in the worst case, dying. However, the current death rate in the UK remains low, despite rising infection rates.

One of Germany's leading virologists, Christian Drosten, said in a Coronavirus Update podcast in June that there were "cases where people who are double-vaccinated also die." He suggested that experts look carefully at the exact cause of death and how the diagnosis was made.

One of Germany's leading virologists Christian Drosten
Virologist Christian Drosten said we need to look carefully at the actual cause of death in delta variant casesImage: Britta Pedersen/dpa/picture alliance

The high proportion of vaccinated individuals among the dead is probably due to the fact that about half of the population is now fully immunized, combined with the fact that numbers of overall deaths are dropping.

Moreover, according to PHE's data, 116 of the 118 people who died were over the age of 50.

Peggy Riese, a scientist at the Helmholtz Center for Infection Research (HZI), explained the scenario with the help of a concrete example. "If 100% of a population is vaccinated, then a few people who are vaccinated also die," she told DW. She said that doesn't mean the vaccine isn't safe, just that it doesn't provide 100% protection.

Additionally, low numbers of vaccinated individuals could die if their inoculations lacked efficacy due to the presence of immunosuppressants, for instance, in those who have had transplants, as Georg Behrens, a professor at the Hanover Medical School's clinic for rheumatology and immunology, recently told DW.

Behrens said the effect of the vaccination also fades after a few months. "Some people can still suffer a serious illness under unfortunate constellations," he said. The vaccines protect very well — but Behrens, too, warned no vaccine can ever provide 100% protection.

A study conducted by the UK's Medical Research Council (MRC) Biostatistics Unit (BSI) at the University of Cambridge suggests vaccinations have prevented around 7.2 million infections and 27,000 deaths in England alone. "The number of infections and deaths prevented by the vaccination program is not only astonishingly high but grows exponentially over the course of the vaccination program," said Paul Birrell, one of the scientists involved in the study.

Good protection after complete vaccination

All of the experts that DW interviewed voiced confidence in the effectiveness of the vaccines against the delta variant. "The vaccinations are fantastic," said virologist Friedemann Weber of the University of Giessen, for example. "The immune response in vaccinated people who have received both doses and wait accordingly, is higher on average, or as high as for people who have received an immune response after an infection," he explained.

Scientific findings support the expert's assessment.

A man getting a coronavirus vaccination in Madrid
A number of studies have shown that full vaccination offers strong protection against the delta variantImage: JAVIER BARBANCHO/REUTERS

According to a recent study published in the journal Nature, a double vaccination from BioNTech-Pfizer continues to protect strongly against the delta variant. However, new data from Israel rates protective effectiveness against the delta variant as somewhat lower than against previous variations.

The Israeli health department announced in a press release that the effectiveness of the BioNTech-Pfizer vaccine against the delta variant in terms of completely preventing infection has fallen to 64%.

Nevertheless, the vaccination continues to protect 93% of individuals from serious infection with hospitalization. It is not transparent how the Israeli health department got the data. So far, the press office has not provided any more detailed information on the procedure in the study despite DW's request.

According to a non-peer reviewed Canadian study from early July, Moderna's COVID-19 vaccine also exhibited high protection against the delta variant. The study said the Moderna vaccine was 72% effective from 14 days after the first dose. The study was published before sufficient data could be collected on protection after two doses.

Vaccine maker Johnson & Johnson (J&J) claims that its jab produced a strong immune response eight months after vaccination. J&J presented its interim results from a study of 20 people that shows that its vaccine produces antibodies against the delta variant. However, no clear amount of efficacy has been stated so far. 

Studies published on vaccination protection against the delta mutation vary greatly, as can be seen in a comparison laid out in the Financial Times

Will a 'booster' become necessary?

Georg Behrens of Hanover Medical School emphasized that it must be taken into account at what point Israelis who were infected with the delta variant had been vaccinated. The first vaccinations were given in December 2020, and Behrens said the effect of the initial inoculation could slowly wear off, making another dose necessary.

The manufacturers of the BioNTech-Pfizer vaccine have also pointed in that direction in their latest press release. In order to maintain efficacy, they are calling for approval of a third vaccination dose six months after the second vaccination.

Are mRNA vaccines better than vector vaccines?

Earlier data from the UK had indicated slightly higher effectiveness of the two mRNA vaccines (BioNTech-Pfizer and Moderna) against hospitalization than the Israeli data showed: According to a PHE study, one dose of the BioNTech-Pfizer vaccination is said to hinder severe illness with hospitalization as a result of the the delta variant by up to 94%, with protection rising to 96% after the second dose.

The PHE study said people vaccinated with AstraZeneca are 71% protected from having a severe course of illness with hospitalization after the first vaccination, and 92% after the second.

According to another study published by PHE, the vaccines also protect against symptomatic reactions to possible infection with the delta variant. In it, BioNTech-Pfizer shows 36% protection against symptomatic disease after the first dose and 88% after the second. AstraZeneca showed 30% protection after the first dose and 67% after the second.

The study results indicate that the delta variant is more resistant to the vaccines but that full vaccination continues to provide strong protection even against this variant.

How likely are more dangerous variants?

Variants arise when the virus mutates. "New variants are likely to come our way for a while," said virologist Friedemann Weber, adding that new variants continue to appear until the majority of the population has been vaccinated. Still, the virologist does not assume vaccinations will suddenly become ineffective.

Fact check: Did COVID vaccines cause the delta variant?

Behrens said it's impossible to accurately predict whether more dangerous variants will appear but said there are always plenty of less dangerous mutations out there that do not prevail.

He said the best protection either way is vaccination, because the more people get vaccinated, the greater the immunity in the population and the smaller the infection rate.

Peggy Riese agreed, saying the coronavirus mutates more frequently than, for example, the measles virus — but less often than the flu virus. So it is neither a virus that mutates particularly quickly nor one that mutates very slowly.

information graphic showing global delta variant infections
The number of covid infections with the delta variant are rapidly increasing worldwide

Do we need new vaccines?

So far, vaccines have proven very effective against all mutations of concern. Riese said vaccines will have to be adapted when they lose their effectiveness. Nevertheless, one shouldn't be too hasty, she warned: "A vaccine isn't developed that quickly either. If a mutant is created every quarter, we can no longer keep up with vaccine development."

It is also possible that a vaccine adapted to a particular variant could become obsolete when that strain mutates again.

Virologist Weber sees things a little differently. "You should adapt the vaccines right away," he said, adding the major studies that have to be done before approval for use take a lot of time.

According to vaccine manufacturer BioNTech-Pfizer, it is already in the process of developing a vaccine specifically designed to combat the delta variant. The first clinical studies are scheduled to begin in August.

Researchers at Berlin's renowned Charite Hospital also assume COVID-19 vaccinations will have to be checked regularly during the pandemic and adjusted if necessary. At the moment, the virus is changing rapidly, as there are many infections worldwide and the virus can therefore develop more quickly, according to a press release.

"Based on the evolution rates of common cold coronaviruses, we assume that SARS-CoV-2 will also change more slowly as soon as the infection process subsides — i.e., after a large part of the global population has built up immune protection either through the disease itself or through a vaccination," explained Jan Felix Drexler of the Charite's Institute of Virology.

As soon as the situation has stabilized, he said, vaccinations will likely be able to be used for longer periods of time.