13 January 2022
What was claimed
Vaccines prevent transmission of the Delta variant of Covid-19 for only eight weeks.
It’s difficult to measure the effect of vaccines on transmission, but available evidence suggests it’s longer than eight weeks and boosters are likely to increase that protection.
What was claimed
Antibodies from a previous Covid-19 infection are probably equivalent to someone who has been vaccinated.
Although natural immunity acquired through Covid-19 infection does protect against subsequent infection, evidence shows that also being vaccinated can increase this protection dramatically. Vaccines also lower the risk of serious illness caused by an infection.
A video by Sky News shows an NHS consultant challenging health secretary Sajid Javid on live television that the “science isn’t strong enough” to support mandatory Covid-19 vaccinations for health service workers.
Critical care consultant Dr Steve James was responding to Mr Javid, who was asking staff at the hospital for their views on the forthcoming requirement for all NHS frontline staff to be vaccinated against Covid-19.
Dr James said he wasn’t vaccinated and had antibodies from a previous infection that protected him from Covid-19 “probably equivalent to someone who’s vaccinated”. He also claimed that vaccines reduce transmission “for only eight weeks with Delta, with Omicron it’s probably less.”
However, evidence suggests his claims aren’t completely correct.
Vaccines can prevent transmission beyond eight weeks
Since the interview, the BBC has reported that Dr James acknowledged his eight week figure was wrong and he was instead referring to a study which claimed that transmission protection only lasted up to 12 weeks.
While this study states that after 12 weeks a person who has been double vaccinated with the AstraZeneca vaccine is only 2% less likely to transmit the delta variant of the virus than an unvaccinated person, it also found that someone double vaccinated with the Pfizer BioNTech vaccine had a 24% lower risk of infecting others after 12 weeks.
It’s worth saying that while there is credible evidence measuring transmission, estimating how long a vaccine prevents transmission may be difficult. A research paper published in November 2021 attempted to create a model to measure the effectiveness of vaccines against transmission. It highlighted that variables such as viral load, susceptibility to the disease and incident rates of Covid-19 are among the challenges that continue to affect the ability of researchers to accurately measure transmission risk, let alone the length of time a vaccine can prevent transmission.
Dr Peter English, a retired consultant in communicable disease control and former editor of the journal Vaccines in Practice, told the Science Media Centre that “It is still early to be clear about the efficacy of vaccination against infection and transmission, and, as with previous variants, such efficacy is likely to decrease over time. A third dose of vaccine […] gives most people a considerable increase in their circulating antibodies, multiplying them to levels that will take some time to fall below protective levels.”
However, Dr English added: “A third dose will push antibody levels much higher than after two doses, so it is likely to take considerably longer for efficacy to drop below protective levels.
“Even if vaccination only halves the likelihood that a healthcare worker will be infected and infect others, that is very valuable.”
We have previously written about the measurable impact that Covid-19 vaccines have on transmission. In a review of evidence on “Indirect Protection by Reducing Transmission” published in May on behalf of the Infectious Diseases Society of America, researchers found “compelling evidence that SARS-CoV-2 vaccination results in a substantial reduction in transmission risk, although the exact magnitude of overall transmission reduction is yet to be fully characterized.”
Vaccines also offer protection from infection and serious illness, and continue to offer protection for many weeks even with just two doses.
A recent UKHSA briefing, which assessed the efficacy of the three vaccines used in the UK against symptomatic Covid-19, found their effectiveness against the Omicron variant disappeared 20 weeks after a second dose alone. The briefing stated the AstraZeneca vaccine became ineffective against Omicron 20 weeks after a second vaccine dose while the Pfizer and Moderna still had around 10% efficacy after that time and dosage.
The briefing stated that a booster led to effectiveness which dropped to 40 to 50% after 10 weeks.
Vaccines offer additional protection to antibodies
Dr James also suggested the protection he had from Covid-19 antibodies from a previous infection “is probably equivalent to someone who’s vaccinated”.
There is also some evidence that suggests the Omicron variant evades immunity from past infection. A report by Imperial College London published in December 2021 estimated that although a study of UK health workers had previously reported that a Covid-19 infection gave 85% protection against reinfection over six months before the Omicron variant emerged, this had fallen to only 19% against Omicron.
Prior to the spread of Omicron, we have previously written that (according to a study yet to be peer reviewed) people who had been double vaccinated against Covid-19 with the Pfizer vaccine were about six times more likely to catch the virus than people who had caught it before, but not been vaccinated.
However, the group who seemed to have the highest level of protection were those who had been infected and received a single dose of the vaccine. The study found that people who were infected but not vaccinated were about twice as likely to test positive again, compared with this infected and vaccinated group
A small scale study published in December 2021 also found that those who had been double vaccinated and infected by Covid-19 had what was called “super immunity,” with an increase of some antibodies beyond 1000% compared to controls.
Correction 14 January 2022
The article originally repeated the claim and conclusion boxes. This has been corrected.
Correction 14 January 2022
We updated this article to correct a typo in Mr Javid’s name and the date in the second paragraph.
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