Covid-19: How effective are vaccines against the delta variant?

The delta variant is now the dominant form of SARS-CoV-2 in the UK and many other countries. How effective the leading vaccines are against this new threat.     

BMJ 2021; 374 doi: https://doi-org.ezproxy.uws.edu.au/10.1136/bmj.n1960 (Published 09 August 2021)

  • Data from Public Health England (PHE) reveal that of all the people who died within 28 days of testing positive for the delta variant between 1 February and 19 July, 49% (224) had had two vaccine doses. Almost all of these people, 220, were aged 50 or older.2
  • As statistician David Spiegelhalter notes, in a population where less-than-perfect vaccines have been distributed widely, one would expect to see deaths occurring among vaccinated people as the virus spreads. And so far, in contrast to the winter when far fewer people had received vaccines, the rate of hospital admissions and deaths in the UK is not rising as sharply as cases.

Warning signs

  • Data up to 4 August from Imperial College London’s React study found that people who said they had received two vaccine doses were half as likely to test positive for covid-19, adjusting for other factors such as age and whether or not they had symptoms.3 The researchers estimated a 50-60% lower risk of infection from the delta variant if a person was double vaccinated.
  • The picture emerging from various countries does, however, suggest that vaccinated people are more likely to experience symptoms after catching the delta variant compared with earlier forms of the virus.

Vaccine efficacy is dropping for the delta-variant 

  • Israeli government suggest that the Pfizer BioNTech jab’s efficacy against symptomatic infection fell from 94% to 64% after the delta variant began spreading in the country.4
  • Public Health Scotland published in the Lancet also show a drop in protection against symptomatic illness,5 from 92% against the alpha variant, which was first detected in the UK, to 79% against delta among people with two doses of the Pfizer BioNTech vaccine.
  • For the Oxford AstraZeneca vaccine, the reduction was from 73% to 60%. Data from Canada, yet to be peer reviewed, also show a drop in efficacy.6

PHE data to date are consistent with estimates that suggest—despite these drops in efficacy—vaccines in use in the UK (Pfizer BioNtech, AstraZeneca, and Moderna) all reduce the risk of death by more than 85%, regardless of variant.

What about transmission?

  • A lingering question is to what extent the vaccines may be losing effectiveness at preventing onward transmission from people who become infected. After all, each of the new variants is characterised by increased transmissibility compared with the original (wild type) SARS-CoV-2.
  • A recently released report from the US CDC suggests that the viral load of vaccinated people infected with the delta variant is similar to that of unvaccinated people.8 People remain less likely to become infected in the first place when they have been vaccinated, however.9

Neutralising antibodies

  • It’s not yet clear how the body’s immune system fights SARS-CoV-2. Without knowing for sure what the correlates of protection are, it’s hard to say why a vaccine may be less effective against variants. Evidence is accumulating, however, that the ability of antibodies to neutralise the delta variant is reduced compared with, say, the alpha variant. They did, however, see a neutralising response in sera from almost all people who had received two doses of a vaccine.
  • It is pointed that a reduction in neutralising antibodies does not necessarily mean that antibodies will fail to have an impact. “I assume that the reason we can still prevent severe disease from the delta variant is that we are generating enough antibody response against the spike protein,” 
  • The bottom line is that delta—a variant with distinct mutations making it much more transmissible, blunting immune protection as much as 10-fold—poses a challenge to the vaccines currently used. But in most people the vaccine induced levels of neutralising antibodies are large enough that even a 10-fold drop keeps them well protected.

  • While it’s sobering to see cases occurring in fully vaccinated people, their protection is holding up well, as judged by numbers of hospital admissions and fatalities relative to what might have been. The message should still be to get vaccinated as soon as possible.

     

Manufacturers confident

හොරාගේ අම්මාගෙන් පෙන අහනව වගේ

“We haven’t seen any evidence that the circulating variants result in a loss of protection provided by the Pfizer BioNTech covid-19 vaccine (BNT162b2) in our laboratory studies,” a spokeswoman for Pfizer told The BMJ.

Similar statements were made by AstraZeneca and Moderna

Despite this universal confidence, however, Pfizer, for one, is at work on an updated version of its vaccine, targeting the delta variant specifically. The company hopes this will enter clinical studies in August.

Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant

The B.1.617.2 (delta) variant of SARS-CoV-2 has contributed to a Covid-19 surge in India and has now been detected across the globe. The effectiveness of the BNT162b2 and ChAdOx1 nCoV-19 vaccines against this variant has been unclear. New research findings are summarized in a short video.

Full Paper – https://www.nejm.org/doi/full/10.1056/NEJMoa2108891

 

The delta variant is now the dominant form of SARS-CoV-2 in the UK and many other countries. How effective the leading vaccines are against this new threat.     

BMJ 2021; 374 doi: https://doi-org.ezproxy.uws.edu.au/10.1136/bmj.n1960 (Published 09 August 2021)

  • Data from Public Health England (PHE) reveal that of all the people who died within 28 days of testing positive for the delta variant between 1 February and 19 July, 49% (224) had had two vaccine doses. Almost all of these people, 220, were aged 50 or older.2
  • As statistician David Spiegelhalter notes, in a population where less-than-perfect vaccines have been distributed widely, one would expect to see deaths occurring among vaccinated people as the virus spreads. And so far, in contrast to the winter when far fewer people had received vaccines, the rate of hospital admissions and deaths in the UK is not rising as sharply as cases.

Warning signs

  • Data up to 4 August from Imperial College London’s React study found that people who said they had received two vaccine doses were half as likely to test positive for covid-19, adjusting for other factors such as age and whether or not they had symptoms.3 The researchers estimated a 50-60% lower risk of infection from the delta variant if a person was double vaccinated.
  • The picture emerging from various countries does, however, suggest that vaccinated people are more likely to experience symptoms after catching the delta variant compared with earlier forms of the virus.

Vaccine efficacy is dropping for the delta-variant 

  • Israeli government suggest that the Pfizer BioNTech jab’s efficacy against symptomatic infection fell from 94% to 64% after the delta variant began spreading in the country.4
  • Public Health Scotland published in the Lancet also show a drop in protection against symptomatic illness,5 from 92% against the alpha variant, which was first detected in the UK, to 79% against delta among people with two doses of the Pfizer BioNTech vaccine.
  • For the Oxford AstraZeneca vaccine, the reduction was from 73% to 60%. Data from Canada, yet to be peer reviewed, also show a drop in efficacy.6

PHE data to date are consistent with estimates that suggest—despite these drops in efficacy—vaccines in use in the UK (Pfizer BioNtech, AstraZeneca, and Moderna) all reduce the risk of death by more than 85%, regardless of variant.

What about transmission?

  • A lingering question is to what extent the vaccines may be losing effectiveness at preventing onward transmission from people who become infected. After all, each of the new variants is characterised by increased transmissibility compared with the original (wild type) SARS-CoV-2.
  • A recently released report from the US CDC suggests that the viral load of vaccinated people infected with the delta variant is similar to that of unvaccinated people.8 People remain less likely to become infected in the first place when they have been vaccinated, however.9

Neutralising antibodies

  • It’s not yet clear how the body’s immune system fights SARS-CoV-2. Without knowing for sure what the correlates of protection are, it’s hard to say why a vaccine may be less effective against variants. Evidence is accumulating, however, that the ability of antibodies to neutralise the delta variant is reduced compared with, say, the alpha variant. They did, however, see a neutralising response in sera from almost all people who had received two doses of a vaccine.
  • It is pointed that a reduction in neutralising antibodies does not necessarily mean that antibodies will fail to have an impact. “I assume that the reason we can still prevent severe disease from the delta variant is that we are generating enough antibody response against the spike protein,” 
  • The bottom line is that delta—a variant with distinct mutations making it much more transmissible, blunting immune protection as much as 10-fold—poses a challenge to the vaccines currently used. But in most people the vaccine induced levels of neutralising antibodies are large enough that even a 10-fold drop keeps them well protected.

  • While it’s sobering to see cases occurring in fully vaccinated people, their protection is holding up well, as judged by numbers of hospital admissions and fatalities relative to what might have been. The message should still be to get vaccinated as soon as possible.

     

Manufacturers confident

හොරාගේ අම්මාගෙන් පෙන අහනව වගේ

“We haven’t seen any evidence that the circulating variants result in a loss of protection provided by the Pfizer BioNTech covid-19 vaccine (BNT162b2) in our laboratory studies,” a spokeswoman for Pfizer told The BMJ.

Similar statements were made by AstraZeneca and Moderna

Despite this universal confidence, however, Pfizer, for one, is at work on an updated version of its vaccine, targeting the delta variant specifically. The company hopes this will enter clinical studies in August.

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut elit tellus, luctus nec ullamcorper mattis, pulvinar dapibus leo.

The delta variant is now the dominant form of SARS-CoV-2 in the UK and many other countries. How effective the leading vaccines are against this new threat.     

BMJ 2021; 374 doi: https://doi-org.ezproxy.uws.edu.au/10.1136/bmj.n1960 (Published 09 August 2021)

  • Data from Public Health England (PHE) reveal that of all the people who died within 28 days of testing positive for the delta variant between 1 February and 19 July, 49% (224) had had two vaccine doses. Almost all of these people, 220, were aged 50 or older.2
  • As statistician David Spiegelhalter notes, in a population where less-than-perfect vaccines have been distributed widely, one would expect to see deaths occurring among vaccinated people as the virus spreads. And so far, in contrast to the winter when far fewer people had received vaccines, the rate of hospital admissions and deaths in the UK is not rising as sharply as cases.

Warning signs

  • Data up to 4 August from Imperial College London’s React study found that people who said they had received two vaccine doses were half as likely to test positive for covid-19, adjusting for other factors such as age and whether or not they had symptoms.3 The researchers estimated a 50-60% lower risk of infection from the delta variant if a person was double vaccinated.
  • The picture emerging from various countries does, however, suggest that vaccinated people are more likely to experience symptoms after catching the delta variant compared with earlier forms of the virus.

Vaccine efficacy is dropping for the delta-variant 

  • Israeli government suggest that the Pfizer BioNTech jab’s efficacy against symptomatic infection fell from 94% to 64% after the delta variant began spreading in the country.4
  • Public Health Scotland published in the Lancet also show a drop in protection against symptomatic illness,5 from 92% against the alpha variant, which was first detected in the UK, to 79% against delta among people with two doses of the Pfizer BioNTech vaccine.
  • For the Oxford AstraZeneca vaccine, the reduction was from 73% to 60%. Data from Canada, yet to be peer reviewed, also show a drop in efficacy.6

PHE data to date are consistent with estimates that suggest—despite these drops in efficacy—vaccines in use in the UK (Pfizer BioNtech, AstraZeneca, and Moderna) all reduce the risk of death by more than 85%, regardless of variant.

What about transmission?

  • A lingering question is to what extent the vaccines may be losing effectiveness at preventing onward transmission from people who become infected. After all, each of the new variants is characterised by increased transmissibility compared with the original (wild type) SARS-CoV-2.
  • A recently released report from the US CDC suggests that the viral load of vaccinated people infected with the delta variant is similar to that of unvaccinated people.8 People remain less likely to become infected in the first place when they have been vaccinated, however.9

Neutralising antibodies

  • It’s not yet clear how the body’s immune system fights SARS-CoV-2. Without knowing for sure what the correlates of protection are, it’s hard to say why a vaccine may be less effective against variants. Evidence is accumulating, however, that the ability of antibodies to neutralise the delta variant is reduced compared with, say, the alpha variant. They did, however, see a neutralising response in sera from almost all people who had received two doses of a vaccine.
  • It is pointed that a reduction in neutralising antibodies does not necessarily mean that antibodies will fail to have an impact. “I assume that the reason we can still prevent severe disease from the delta variant is that we are generating enough antibody response against the spike protein,” 
  • The bottom line is that delta—a variant with distinct mutations making it much more transmissible, blunting immune protection as much as 10-fold—poses a challenge to the vaccines currently used. But in most people the vaccine induced levels of neutralising antibodies are large enough that even a 10-fold drop keeps them well protected.

  • While it’s sobering to see cases occurring in fully vaccinated people, their protection is holding up well, as judged by numbers of hospital admissions and fatalities relative to what might have been. The message should still be to get vaccinated as soon as possible.

     

Manufacturers confident

හොරාගේ අම්මාගෙන් පෙන අහනව වගේ

“We haven’t seen any evidence that the circulating variants result in a loss of protection provided by the Pfizer BioNTech covid-19 vaccine (BNT162b2) in our laboratory studies,” a spokeswoman for Pfizer told The BMJ.

Similar statements were made by AstraZeneca and Moderna

Despite this universal confidence, however, Pfizer, for one, is at work on an updated version of its vaccine, targeting the delta variant specifically. The company hopes this will enter clinical studies in August.

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut elit tellus, luctus nec ullamcorper mattis, pulvinar dapibus leo.

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