Can vaccination boosters halt the spread of the delta form of SARS-CoV-2?

The Delta form of SARS-CoV-2, the virus that causes COVID-19, is more transmissible than previous variations, and it has swiftly established itself as the dominant variety in numerous countries, including India and the United Kingdom. According to certain findings, current COVID-19 vaccinations may be less effective at preventing Delta infection. Additional booster injections may be beneficial.

Can vaccination boosters halt the spread of the delta form of SARS-CoV-2? - Photo by Eva Marie Uzcategui/Bloomberg via Getty Images
Can vaccination boosters halt the spread of the delta form of SARS-CoV-2? – Photo by Eva Marie Uzcategui/Bloomberg via Getty Images


In recent months, the Delta form of SARS-CoV-2 has spread rapidly around the world, becoming the predominant variety in many locations.

Its fast growth has lately prompted countries like Australia to tighten lockdowns since emerging evidence shows the variation is more infectious than pre-existing variants, such as the Beta variant, and may be able to evade current COVID-19 vaccines in some circumstances.

Prof. Sir Andrew Pollard, leader of the Oxford Vaccine Group, which contributed to the creation of the Oxford-AstraZeneca vaccine, has even stated that establishing herd immunity is impossible due to the highly transmissible Delta form.

“Vaccinated individuals will continue to be infected with the Delta variety. And it means that everyone who is still unvaccinated will come into contact with the virus at some time, and we don’t have anything that would [fully] prevent transmission,” he told The Guardian.

Additionally, new results indicate that the protection conferred by COVID-19 vaccinations diminishes significantly with time, implying that vaccinated persons become more vulnerable to SARS-CoV-2 infection.

However, some scientists and pharmaceutical firms think that adding a booster injection to some of the most commonly licensed COVID-19 vaccines might be a viable strategy to ward off the Delta version.

However, what data exists to date, and how are nations responding to the idea of include additional booster doses in their COVID-19 immunization campaigns?

Preliminary studies indicate that boosters are effective.

While published data on the efficacy of COVID-19 vaccination boosters against the Delta variant are not yet available, several pharmaceutical firms that manufacture and sell COVID-19 vaccines have said that recent clinical trials support this position.

According to Pfizer’s 2021 second-quarter earnings report, getting a booster dose of their COVID-19 vaccine after receiving the initial two doses boosts the level of Delta variant antibodies fivefold in adults aged 18–55 and elevenfold in those aged 65–85.

In response to Medical News Today’s inquiries, a Pfizer spokesman stated that this “conclusion is based on preliminary results from an ongoing booster study of the existing BNT162b2 vaccination and laboratory tests.”

“The booster trial builds on the phase 1/2/3 trial and is part of the firms’ clinical development plan to evaluate the efficacy of a third dosage against developing variants,” they said, adding that Pfizer “expect[s] to publish more definite results regarding the analysis in the coming weeks.”

This third dosage would be equivalent to the presently authorized Pfizer vaccine’s two doses. However, the firm is also evaluating the efficacy of an “updated” vaccination dosage that has been modified to precisely target the Delta strain.

According to a Pfizer spokesman, MNT:

“The continuing booster study is examining the existing BNT162b2 vaccine’s safety and acceptability. While we believe that the third dose of BNT162b2 has the potential to maintain the highest levels of protective efficacy against all currently known variants, including Delta, we are remaining vigilant and developing an updated version of the vaccine that targets the Delta variant’s complete spike protein. The trial’s initial batch of mRNA has already been produced, and we anticipate initiating clinical investigations in August, pending regulatory approval.”

Additionally, Moderna stated that an additional booster injection of their COVID-19 vaccine would be sufficient to ward off the Delta version.

The firm first announced this in its own second-quarter financial report, stating that “[r]obust antibody responses have been reported in phase 2 trials using current Moderna booster candidates against COVID-19.”

“Vaccination with 50 [micrograms] of three distinct Moderna mRNA booster candidates produced strong antibody responses […] against key variations of concern, including Gamma (P.1), Beta (B.1.351), and Delta (B.1.617.2),” the paper adds.

Among the three boosters under consideration were their already approved injection and two additional experimental options.

According to Moderna’s study, neutralizing antibody levels created following the third booster injection were comparable to those reported following two 100 microgram doses of their presently approved vaccine.

Booster injections have previously been authorized?

As a result of these findings, both Pfizer and Moderna have sought approval for their respective booster injections from nations that have previously authorized their primary COVID-19 vaccines.

The Food and Drug Administration (FDA) has approved third booster doses of both the Pfizer and Moderna COVID-19 vaccines — but only for people who are immunocompromised and hence at increased risk of infection with developing strains of SARS-CoV-2.

Israel has also just allowed the delivery of third doses of the Pfizer vaccine, which are now accessible to “people over the age of 50, healthcare personnel, those with significant coronavirus risk factors, [and] inmates and wardens.”

While the United Kingdom has not yet authorized further booster injections, unconfirmed sources claim the country has ordered millions of more doses for an autumn 2022 COVID-19 vaccine booster campaign.

“We have obtained over 500 [million] doses of COVID-19 vaccine and are optimistic that our stockpile will sustain future booster campaigns. The Department of Health and Social Care informed The Guardian that the possible booster program “will be based on the final opinion of the independent [Joint Committee on Vaccination and Immunisation].”

WHO bans booster injections?

While booster shots may help protect against emerging SARS-CoV-2 variants, the World Health Organization (WHO) has expressed concern that rapid distribution of third vaccine doses in high-income countries will exacerbate vaccine nationalism and widen the vaccination gap in low- and middle-income countries.

“I appreciate all countries’ desire to safeguard their citizens against the Delta version. However, we cannot tolerate nations who have already consumed the majority of the global vaccination supply utilizing more vaccines,” stated Dr. Tedros Adhanom Ghebreyesus, Director-General of the World Health Organization, during a news conference on August 4.

To help close this growing gap, the WHO has advised high-income nations at the forefront of vaccine development and delivery to refrain from offering further booster doses until at least September 2021.

“We urgently need to shift the bulk of vaccinations away from high-income countries and toward low-income ones,” Dr. Tedros underlined.

When may boosters be required?

Dr. Laith Jamal Abu-Raddad, an infectious disease epidemiologist at Weill Cornell Medicine–Qatar in Doha, argues in a news story for NatureTrusted Source that the advantages of providing extra booster doses to individuals already fully vaccinated against COVID-19 are limited.

According to Dr. Abu-Raddad, this would entail “spending resources on boosters for individuals already protected against serious illness.”

“Perhaps in the future, we will need to consider [providing booster dosages]. However, we do not have compelling grounds for it at the moment,” he argues.

Additionally, the manufacturers of widely licensed COVID-19 vaccines have maintained that their vaccinations provide adequate protection against the development of serious illness.

A Pfizer representative stressed to MNT:

“It is important mentioning that we continue to have confidence in the protection provided by the two-dose Pfizer/BioNTech COVID-19 vaccine (BNT162b2), which continues to demonstrate excellent effectiveness in avoiding severe illness and hospitalizations.”

“However,” they said, “we are continuing to take parallel actions and follow the science, as we have done since the outbreak began. We believe that by taking simultaneous actions and keeping attentive, we can stay one step ahead of this virus.”

Prof. Robert Aldridge, an infectious disease epidemiologist at the University College London in the United Kingdom, provides some warning remarks in a response to Nature. He notes that deciding whether or not to allow more booster dosages in the near future will be a “tough choice,” almost probably based on inadequate information, as researchers continue to assess the true advantages of experimental boosters.

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