Credit ACIP/CDC
#15,937
Although we've seen some reassuring studies, there remains a good deal of uncertainty over how protective current vaccines are likely to be against the growing panoply of SARS-CoV-2 variants, a list that includes the B.1.1.7 (UK), B.1.351 (South African), P.1 - P.2 - P.3 lineages (Brazil), and the recently emerged Indian Variants (B.1.617).
Some protection, perhaps focused more on reducing the severity of one's illness, seems likely. But some of these emerging variants may be more likely to produce breakthrough infections than the `classic covid' virus.
On Friday the journal Science published a study, conducted by Imperial College London, on partially vaccinated (1-dose Pfizer) Healthcare Workers (HCWs) (some who had previously contracted COVID) and found that those who had a prior COVID infection and 1-dose of the vaccine mounted a much better immune response than those who had not been previously infected.
In countries that have adopted a delayed roll-out of the 2nd dose, in order to get as many people vaccinated with the first dose, this could be problematic.
We've excerpts from press release from Imperial College London, followed by a link and the Abstract from the study. I'll have a brief postscript after the break:
Prior SARS-CoV-2 infection boosts response to variants after first vaccine dose
by Ryan O'Hare 30 April 2021
A single dose of vaccine boosts protection against SARS-CoV-2 coronavirus variants, but only in those with previous COVID-19, a study has found.
In those who have not previously been infected and have so far only received one dose of vaccine the immune response to variants of concern may be insufficient.
The findings, published today in the journal Science and led by researchers at Imperial College London, Queen Mary University of London and University College London, looked at immune responses in UK healthcare workers at Barts and Royal Free hospitals following their first dose of the Pfizer/BioNTech vaccine.*
They found that people who had previously had mild or asymptomatic infection had significantly enhanced protection against the Kent and South Africa variants, after a single dose of the mRNA vaccine. In those without prior COVID-19, the immune response was less strong after a first dose, potentially leaving them at risk from variants.
Professor Rosemary Boyton, Professor of Immunology and Respiratory Medicine at Imperial College London, who led the research, said: “Our findings show that people who have had their first dose of vaccine, and who have not previously been infected with SARS-CoV-2, are not fully protected against the circulating variants of concern. This study highlights the importance of getting second doses of the vaccine rolled out to protect the population.”
Blood samples were analysed for the presence and levels of immunity against the original strain of SARS-CoV-2, as well as the Kent (B.1.1.7) and South Africa (B.1.351) variants of concern. Along with antibodies – the Y-shaped proteins which stick to the virus and help block or neutralize the threat – the researchers also focused on two types of white blood cell: B-cells, which ‘remember’ the virus; and T cells, which help B cell memory and recognise and destroy cells infected with coronavirus.
However, in people without previous SARS-CoV-2 infection, a single vaccine dose resulted in lower levels of neutralizing antibodies against SARS-CoV-2 and the variants, potentially leaving them vulnerable to infection and highlighting the importance of the second vaccine dose.They found that after a first dose of vaccine, prior infection was associated with a boosted T cell, B cell and neutralizing antibody response, which could provide effective protection against SARS-CoV-2, as well as the Kent and South Africa variants.
The team looked at two variants of concern, however, they think it possible that the findings will apply to other variants in circulation, such as the Brazil (P.1) and India (B.1.617 and B.1.618) variants.
It remains unclear precisely how much protection is offered by T cells. Interestingly, the mutations in the Kent and South Africa variants here resulted in T cell immunity which could be reduced, enhanced or unchanged compared to the original strain, depending on genetic differences between people.
Professor Boyton commented: “Our data show that natural infection alone may not provide sufficient immunity against the variants. Boosting with a single vaccine dose in people with prior infection probably does. As new variants continue to emerge, it is important to fast track global rollout of vaccines to reduce transmission of the virus and remove the opportunities for new variants to arise.”
‘Prior SARS-CoV-2 infection rescues B and T cell responses to variants after first vaccine dose’ by Reynolds, CJ. et al. is published in Science. DOI: 10.1126/science.abh1282
The work builds on previous findings published earlier this year in The Lancet.
The full study can be read at:
Abstract
SARS-CoV-2 vaccine rollout has coincided with the spread of variants of concern. We investigated if single dose vaccination, with or without prior infection, confers cross protective immunity to variants. We analyzed T and B cell responses after first dose vaccination with the Pfizer/BioNTech mRNA vaccine BNT162b2 in healthcare workers (HCW) followed longitudinally, with or without prior Wuhan-Hu-1 SARS-CoV-2 infection.
After one dose, individuals with prior infection showed enhanced T cell immunity, antibody secreting memory B cell response to spike and neutralizing antibodies effective against B.1.1.7 and B.1.351. By comparison, HCW receiving one vaccine dose without prior infection showed reduced immunity against variants. B.1.1.7 and B.1.351 spike mutations resulted in increased, abrogated or unchanged T cell responses depending on human leukocyte antigen (HLA) polymorphisms.
Single dose vaccination with BNT162b2 in the context of prior infection with a heterologous variant substantially enhances neutralizing antibody responses against variants.
Two points worth noting:
First, these studies are based on the subject's post-vaccination levels of T cell immunity, antibody secreting memory B cells, and neutralizing antibodies which are presumed to be effective against infection by the B.1.1.7 and B.1.351 variants.
How these levels translate into to real-world protection, particularly on an individual basis, isn't completely known. Hence their wording that their findings indicate ". . . potentially poor protection against B.1.1.7 and B.1.351 in individuals who have experienced natural infection or who have only had one vaccine dose."
Second, while only two variants were tested, the researchers believe the results might hold true for both the Brazilian and Indian variants.
Those technical caveats aside, it is almost certainly true that one shot from the mRNA vaccine is less protective than two shots, regardless of whether we are talking about `classic covid' or a variant.
In light of these findings, those who have put off that second dose might want to reconsider their decision.
