Source: Vaccine News  Jan 26, 2021  1 year ago
Vaccine News: British Study Warns That Current COVID-19 Vaccines Will Not Be Able To Attain Herd Immunity To SARS-CoV-2 Coronavirus
Vaccine News: British Study Warns That Current COVID-19 Vaccines Will Not Be Able To Attain Herd Immunity To SARS-CoV-2 Coronavirus
Source: Vaccine News  Jan 26, 2021  1 year ago
Vaccine News: A new study by researchers from University of East Anglia, Norwich-UK led by Professor Dr Alastair Grant and Professor Dr Paul R Hunter indicates that the current COVID-19 vaccines will not be able to attain herd immunity against the SARS-CoV-2 coronavirus.

While the COVID-19 pandemic continues to claim thousands of lives each day and cause severe disruptions to ordinary life the world over, scientists persist in searching for a vaccine that will help achieve herd immunity to the virus.
To date, the earliest vaccines by Pfizer, Moderna, Astra-Zeneca, Sinopharm and other pharmaceuticals are already being rolled out in England, the USA, China, India, and a variety of other countries.
This new study assesses whether herd immunity to COVID-19 is a realistic outcome of any immunization program with the two main vaccines currently licensed in the UK. (Pfizer vaccine BNT162b2 and Astra Zeneca/Oxford vaccine ChAdOx1-S)
Importantly the key question is whether these vaccines can achieve a sufficient level of population immunity to reduce R, the reproduction number of the infection, to below one in the absence of any non-pharmaceutical interventions.
The study findings were published on a preprint server and are currently being peer reviewed.
What Is RO?
The R0, pronounced “R naught,” is a mathematical term that indicates how contagious an infectious disease is. It’s also referred to as the reproduction number. As an infection is transmitted to new individuals, it reproduces itself.
The R0 tells you the average number of people who will contract a contagious disease from one person with that disease. It specifically applies to a population of people who were previously free of infection and haven’t been vaccinated.
For instance, if a disease has an R0 of 18, a person who has the disease will transmit it to an average of 18 other people. That replication will continue if no one has been vaccinated against the disease or is already immune to it in their community.
There are possibilities exist for the potential transmission or decline of a disease, depending on its R0 value:
-If R0 is less than 1, each existing infection causes less than one new infection. In this case, the disease will decline and eventually die out.
-If R0 equals 1, each existing infection causes one new infection. The disease will stay alive and stable, but there won’t be an outbreak or an epidemic.
-If R0 is more than 1, each existing infection causes more than one new infection. The disease will be transmitted between people, and there may be an outbreak or epidemic.
Importantly, a disease’s R0 value only applies when everyone in a population is completely vulnerable to the disease. This means:
-no one has been vaccinated
-no one has had the disease before< br /> -there’s no way to control the spread of the disease
Currently the R0 for COVID-19 is a median of 5.7, according to a study published online in Emerging Infectious Diseases. That’s about double an earlier R0 estimate of 2.2 to 2.7
This 5.7 means that one person with COVID-19 can potentially transmit the coronavirus to 5 to 6 people, rather than the 2 to 3 researchers originally thought.
Scientists calculated the new number based on data from the original outbreak in Wuhan, China. They used parameters like the virus incubation period (4.2 days) how much time elapsed from when people were exposed to the virus and when they started to show symptoms.
The scientists estimated a doubling time of 2 to 3 days, which is much faster than earlier estimates of 6 to 7 days. The doubling time is how long it takes for the number of coronavirus cases, hospitalizations, and deaths to double. The shorter the time, the faster the disease is spreading.
Importantly with an R0 of 5.7, at least 82 percent of the population needs to be immune to COVID-19 to stop its transmission through vaccination and herd immunity.
Understanding Vaccine Efficacy
The R0 at the beginning of the pandemic was estimated as 2.87, but with the emergence of the D614G strain, it became a little higher, currently estimated to be 3.72.  and now estimated at 5.7. A new variant, dubbed the British variant (Lineage B.1.1.7, termed Variant of Concern VOC-202012/01), is thought to have higher transmissibility than the ancestral strain, with the R0 being 1.5 times higher. If the original value of 2.87 is used, then the current R0 for B.1.1.7 would be 4.48, while for the higher value of 3.72, the new lineage would have an R0 of 5.80.(lets assume at this levels at now at the even higher value of 5.7)
The study team from the University of East Anglia noted that the efficacy of 95% is recorded in the regulatory approval documents for the Pfizer and Moderna vaccines, and of 70% against the symptomatic illness for the Oxford vaccine. The latter was derived from data pooled from two different dose regimens.
The American Pfizer vaccine has the potential to stop viral shedding from the nose from the first-day post-vaccination, judging from the data in non-human primate studies, though human studies on this aspect have not been conducted. The Oxford Astra-Zeneca vaccine is not fully effective against asymptomatic infections. However, since these are somewhat less infectious (65%) than symptomatic cases, it still reduces transmission but may not entirely prevent it.
Importantly the Oxford vaccine is meant to prevent serious illness and symptomatic illness, though the former is more commonly achieved. It is relatively ineffective against asymptomatic infection, estimated to account for 15% of total transmission. When total incidence is considered, this brings its efficacy against all infections down to 52.5% from the pooled data.
Calculated Population Coverage/Protection
Should we assume the reproduction number (R0) of the SARS-CoV-2 virus to be taken as 2.87, the population coverage with the Pfizer and Oxford vaccines would need to be 69% and 93%, respectively, to bring the R0 below 1.
The infection would need to spread through almost 90% of the population to achieve an R0 less than 1.
However with the higher R0 of 4.48, vaccination with the Pfizer vaccine would have to cover 82% of the population to prevent further spread of this variant.
In the scenario of even if 100% coverage was achieved with the Oxford vaccine, the R0 would drop only to 1.325, preventing effective containment. When asymptomatic infections are included, the R0 goes up by a fifth or more, from 1.325 to 1.6, even assuming 100% coverage with this vaccine. This is because vaccinated individuals can still contract an asymptomatic infection, transmitting the virus to the unvaccinated or those with weakened immunity.
As neither vaccine is meant to be given to children, this will push up the R0 to 2.2, say the researchers, even with 100% coverage with the Oxford vaccine. While being more effective in asymptomatic infection, the mRNA Pfizer vaccine may still be unable to fully arrest the pandemic because it is not approved for pediatric use, allowing viral spread among children.
In the case of the Pfizer vaccine, if all adults are vaccinated and a sizable number of children become immune due to natural infection with SARS-CoV-2, the transmission should drop below sustainable levels, with the R-value below 1.
The study team concludes that vaccines in current use against SARS-CoV-2 infection can prevent serious illness in a substantial majority of cases among those who have received the vaccine. The Oxford vaccine claims only this function. With the mRNA Pfizer vaccine, non-human primate studies indicate that it may have the ability to stop the virus from being shed through the nasal secretions, thus reducing its spread.
It is claimed without real substantial proof that both vaccines will protect the most vulnerable individuals from severe or critical COVID-19. However, this hinges on adequate coverage.
With surveys revealing that a substantial minority of people are unwilling to take the vaccine even when available, full protection is likely to be only a dream for some time to come.
However, given the potential for asymptomatic infection in those who receive the Oxford vaccine, the researchers recommend that at least among those professions that involve numerous contacts with other people, including all healthcare and social workers, a vaccine that protects against asymptomatic infection should be strongly preferred. This will avoid the false security resulting from vaccination with a vaccine that prevents symptomatic illness but may still allow transmission.
Also importantly, since the Oxford vaccine allows the virus to continue circulating, it is quite possible that the virus may adapt by increased transmission efficiency or escape mutations to current neutralizing antibodies. This would make revaccinating with another vaccine that prevents infection altogether a top priority.
Furthermore, the evidence that the Pfizer vaccine limits asymptomatic transmission is indirect and must be updated by actual human data.
The reasons for the lower efficacy of the Oxford vaccine should also be explored, as well as for the variations in the effectiveness of the two-dose regimens, where the low dose/standard dose regimen appears to have led to a higher level of protection than two standard doses. The role played by the difference in intervals between the doses should be examined.
The researchers conclude, “Nonetheless, with these currently approved vaccines, herd immunity to COVID-19 will be very difficult to achieve. It appears likely that non-pharmaceutical interventions (NPIs) will need to be continued for some time, at least.”
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Feb 05, 2020  2 years ago
Source : Thailand Medical news