Latest study shows two shots of Pfizer vaccine effective vs Delta - but getting second shot vital

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  • Two doses of Pfizer's Covid vaccine are nearly as effective at preventing infection with the Delta variant as they are against the Alpha variant.
  • The findings are based on vaccinations in England and were published in a reputable journal this week.
  • The authors said this underscores the importance of people receiving both doses.

With the highly infectious Delta coronavirus variant having only recently begun to dominate Covid-19 infections in some countries, the effectiveness of vaccines against this variant has been unclear. 

The latest, real-world data from England, however, show that people fully vaccinated with the Pfizer-BioNTech vaccine were 88% protected against symptomatic infection with the Delta variant. In people who had received only the first dose, the effectiveness was just 30.7%, underscoring the importance of getting the second shot.

The study was published this week in the New England Journal of Medicine and was led by Dr Jamie Lopez Bernal from Public Health England (PHE).

The researchers compared the effectiveness of the vaccine against the Delta variant with its effectiveness against the Alpha variant (first identified in the UK), which was the predominant virus variant between January and May 2021 in the UK – before the Delta variant took over, causing a surge in cases. The vaccine was found to be 48.7% effective after the first shot and 93.7% after the second shot. 

The difference in vaccine effectiveness after two doses is, therefore, “small” and the findings of the study “would support efforts to maximise vaccine uptake with two doses among vulnerable populations”.

Limitations of study

Unlike the randomised, double-blind, placebo-controlled vaccine trials, this study used what’s known as a test-negative design – a popular approach for estimating vaccine effectiveness – which involved data on all individuals in England who received Covid vaccinations up to 16 May 2021.

The team also incorporated whole-genome sequencing in order to identify whether people who tested positive for the virus were infected with the Delta or Alpha variants.

They did, however, note that their study has several limitations, including that they are observational and should, therefore, be interpreted with caution.

They also said that the numbers of cases analysed and follow-up periods weren't sufficient enough to estimate how well the two doses protected against severe disease, including hospitalisation and death.

AstraZeneca vaccine also tested

Additionally, the researchers tested the level of protection offered by the AstraZeneca-Oxford vaccine, which is one of four vaccines – the others being Pfizer, Moderna, and the single-shot Johnson & Johnson jabs – approved for use throughout the UK.

The results after one dose of the AstraZeneca vaccine were similar to those of Pfizer’s, but in the case of two doses, this dropped from 74.5% for the Alpha variant to 67% for the Delta variant.

South Africa sold about 1 million doses of the AstraZeneca vaccine to the African Union earlier this year after a small study revealed that the vaccine had low efficacy against mild illness caused by the Beta variant, which dominated SA’s second wave, News24 reported

The Delta variant spread rapidly across South Africa and was confirmed to be circulating in all nine provinces earlier this month.

Pfizer booster shot

Pfizer and BioNTech also plan to file for US emergency use authorisation for a booster dose of their vaccine, the company announced this month

“During this period the Delta variant is becoming the dominant variant in Israel as well as many other countries … That is why we have said, and we continue to believe that it is likely, based on the totality of the data we have to date, that a third dose may be needed within six to 12 months after full vaccination,” it said.

In addition to the booster dose, the pharmaceutical company also said that they were developing an updated version of the vaccine that targets Delta specifically. The first batch of the messenger RNA (mRNA) for the new trial has already been manufactured and clinical studies are expected to kick off as early as August 2021, subject to approval, they said. 

Deal with SA facility

According to Fin24, Pfizer and BioNTech agreed to partner with SA’s Biovac Institute to make their Covid vaccine at a facility in Cape Town and deliver more than 100 million doses annually to African nations.

Biovac will obtain the drug substance from facilities in Europe, and manufacturing of finished doses will begin in 2022. 

*For more Covid-19 research, science and news, click here. You can also sign up for our Daily Dose newsletter here.

READ | Covid-19 vaccine safety: We speak to Pfizer's medical director in SA – Part 1

READ | Covid-19 vaccine safety: We speak to Pfizer's medical director in SA – Part 2

READ | Covid-19: Pfizer to seek approval for booster shot and may pursue trial for 'updated' vaccine

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