Following vaccination, scientists believed that communities would build herd immunity to SARS-CoV-2, lowering the risk of infection even for those without antibodies to the virus.
Prof. Andrew Pollard, leader of the Oxford Vaccine Group, believes herd immunity is “not a possibility” given the Delta form of SARS-transmissibility. CoV-2’s
Despite the difficulties posed by this rapidly spreading variety, other health professionals remain optimistic.
Prof. Andrew Pollard, director of the Oxford Vaccine Group, asserts that herd immunity is “not a possibility” in light of the emergence of the SARS-CoV-2 Delta strain.
Prof. Pollard, who also serves as chair of the Joint Committee on Vaccination and Immunisation, which advises the United Kingdom government, was testifying before Members of the United Kingdom’s House of Commons.
His comments come in response to the preprint publication of the latest results from the Real-time Assessment of Community Transmission 1 (REACT 1) research, which indicates that COVID-19 vaccinations are only 49% effective against the Delta form of SARS-CoV-2.
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Immunity of the herd
Since the outbreak of SARS-CoV-2 became a pandemic, scientists had anticipated that people may build herd immunity to the virus following an efficient vaccination campaign.
Haley E. Randolph, a Ph.D. candidate at the University of Chicago in Illinois, and Dr. Luis Barreiro, an Associate Professor at Chicago, write in the journal Immunity that herd immunity refers to a situation in which so many individuals in a population are immune to a virus that it ceases to spread and may even decline.
As a result, even those who lack an antibody response to the virus are protected to some extent.
However, experts have expressed worry that the Delta form of SARS-CoV-2, which has been spreading throughout the United Kingdom and other nations worldwide, is highly transmissible, potentially impairing the efficiency of COVID-19 vaccines.
The Delta variant’s dilemma
This appears to be corroborated by data provided in preprint form by scientists at Imperial College London, United Kingdom, who were responsible for the REACT 1 study.
The last phase of the study, which tested up to 150,000 people in England randomly for COVID-19, revealed that the Delta variation was completely prevalent and had decreased the efficacy of COVID-19 vaccinations to 49%.
Prof. Pollard said that herd immunity is no longer a possibility as a result of this. If SARS-CoV-2 is still capable of spreading to a substantial proportion of fully vaccinated individuals, those who lack an immune response to the virus are at risk of infection.
Prof. Pollard notes that “the issue with this virus is that it is not measles.” If 95% of the population is immunized against measles, the virus cannot spread in the community.”
“Vaccinated individuals will continue to be infected with the Delta variety. And that does mean that everyone who is still unvaccinated will come into contact with the virus at some time, and we now lack a vaccine that can totally prevent transmission.” — Andrew Pollard, Ph.D.
Prof. Sheena Cruickshank, of the University of Manchester’s Division of Infection, Immunity, and Respiratory Medicine, explained to MNT that “herd immunity typically refers to the proportion of a population that needs to be immune to an infection in order to protect those who cannot be immune, and vaccination is the safest way to achieve this.”
“To achieve genuine herd immunity, a high degree of vaccination is required, as well as proof of sterile immunity, which means that you cannot catch the virus against which you have been vaccinated.”
“With [COVID-19], we are not seeing evidence of full sterile immunity in all individuals, whether from the vaccination or past infection — rather, for many, there appears to be some protection against symptomatic illness or severe disease,” she noted.
“As a result, vaccinated individuals may still become sick and transfer the virus to others. [However,] there is overwhelming evidence that vaccinated individuals spread far less virus than uninfected individuals.”
Prof. Pamela Vallely, also of the University of Manchester’s Division of Infection, Immunity, and Respiratory Medicine, told MNT that Prof. Pollard is correct in asserting that herd immunity is no longer viable.
“The critical issue is that the vaccination does not prevent transmission of the Delta version, and additional variations — which will also be able to avoid complete protection — are likely to emerge as long as there is widespread viral replication,” she explained.
Defending against severe illness
Nonetheless, both Prof. Cruickshank and Prof. Vallely assert that, based on the most recent statistics, there are still positives.
Prof. Cruickshank stated that “[t]he vaccine’s efficacy has been somewhat lowered in the Delta version but remains high enough to provide adequate protection against symptomatic and severe illness.” [This] is consistent with the findings of [the REACT 1] report, which indicated that the majority of hospitalizations occur among unvaccinated individuals.”
According to Prof. Vallely, “we may still be positive locally because the vaccination is preventing serious disease in the majority of patients.” Thus, while it appears to be able to infect and multiply in some vaccinated individuals, the great majority of those individuals do not become unwell, or do not become severely ill.”
What about booster shots?
Prof. Cruickshank and Prof. Vallely feel booster injections are only essential for those who are extremely susceptible to the illness because to the vaccinations’ efficacy in guarding against severe COVID-19.
Prof. Cruickshank stated that “because we have evidence of immune memory that is durable and protects against symptomatic infection and reduces transmission […], there appears to be no reason at this time to give boosters to those over the age of 50, as is being considered, although this should be reconsidered as additional data become available.”
Another consideration is whether booster doses of the vaccine should be administered in nations where the great majority of individuals have not yet received their first dose.
Prof. Vallely noted that, in addition to any ethical concerns concerning vaccine distribution, there is a medical reason for ensuring that as many populations as possible are completely vaccinated, a viewpoint Prof. Cruickshank recently endorsed in an editorial article.
Prof. Vallely stated, “[I]t would benefit everyone on the planet to lower the worldwide level of viral replication.” As long as there is widespread transmission, there is widespread replication, which means that the virus has a greater chance of evolving into a more severe form and/or moving further away from the control of vaccines.”
“While I am not equipped to make ethical judgments, it makes scientific sense to vaccinate as many people as possible throughout the globe as fast as possible to contain the pandemic,” she added.