1/ How long do 2 doses of #COVID19 vaccines protect for? Who needs booster vaccinations?

Our team @phe_uk have just published a pre-print on vaccine effectiveness (VE) and duration of protection after 2 doses of Pfizer and AZ vaccines in adults … 🧵

👉 khub.net/documents/1359…
2/ We now have data for ~6 months post-vaccination & compare VE by age, comorbidity & #sarscov2 strain (Alpha/Delta)

We used a test-negative case-control design to estimate VE after 2 doses against PCR-confirmed disease, hospitalisation within 14d of PCR test & death within 28d
3/ In this analysis, 2 million adults (38.7%) had 2x AZ, 1.7 million (31.7%) had 2x Pfizer, 124k (2.4%) had 2x Moderna & 10k (0.2%) had mixed/other

There were 1.5 million cases (544k Alpha, 895k Delta, 37k other/unknown) & 3.8 million negative tests from 3.3 million adults
4/ VE against symptomatic disease peaked in the early weeks after 2nd dose, then fell to 47.3% (95% CI 45.0 to 49.6) by 20+ weeks against the Delta variant for AZ vaccine & 69.7% (95% CI 68.7 to 70.5) for Pfizer vaccine
5/ HOWEVER, there was little waning in protection against hospitalization, with a VE against Delta variant of 77.0% (70.3 to 82.3) beyond 20 weeks post-vaccination for the AZ vaccine & 92.7% (90.3 to 94.6) for Pfizer vaccine.

High protection for both vaccines against death, too
6/ When compared by age, VE against hospitalisation remained high for 20+ weeks. In general, there was more waning in protection against hospitalisation among 65+ compared to 45-64 year-olds.

Note: wide overlapping CI for 40-64y with AZ vaccine at 20+ weeks due to limited data
7/ VE by clinical risk group: very high VE retained for 20+ weeks for both vaccines in adults who were not in a clinical risk group

VE in risk groups started lower & had more waning vs adults not in a risk group, but note wide confidence intervals because of smaller cohorts
8/ Among 40-64-year olds in a clinical risk group, there was some evidence of waning of protection against hospitalization with time since vaccination after 2 doses of AZ vaccine

Virtually no waning of protection against hospitalization for 20+ weeks in healthy 40-63 year-olds
9/ Interestingly, 80+ year-olds receiving Pfizer at shorter interval (<4 weeks) between doses had lower VE compared to an extended interval (≥ 8 weeks) between doses in the latest follow-up periods (>20 weeks after dose 2), although confidence intervals were wide & overlapping
10/ In conclusion, high overall VE is sustained against hospitalisation & death for >5 months post-vaccination

In general, more waning seen with AZ vs. Pfizer, older vs. younger adults and being in a clinical risk group - important info when considering booster prioritisation
11/ Food 4 thought:

👉Could we have waited a little longer before giving boosters? Balance between waning immunity, speed of vaccination, hospital pressures & risk of new variants

👉Although easier to use same vaccines, lower dose +/- variant vaccines might make better boosters

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More from @ShamezLadhani

12 Sep
1/ Our paper on #SARSCoV2 infection, seroconversion and antibody positivity rates in English secondary schools following the emergence of the Alpha variant (B.1.1.7) is now online.

Here’s what we found …🧵

👉 journalofinfection.com/article/S0163-…
2/ We tested #SARSCoV2 infection and serum antibodies in nearly 2,000 staff and students attending 18 secondary schools in 6 English regions during Sep 2020, Dec 2020 and March 2021. Most students did not return to school after the Christmas holidays until their tests in Mar 2021 Image
3/ In March 2021, 1895 participants (1100 students:795 staff) were tested; 5.6% (61/1094) students and 4.4% (35/792) staff had laboratory-confirmed SARS-CoV-2 infection from December 2020-March 2021
Read 8 tweets
12 Aug
1/ Following a barrage of Twitter abuse because of my quote about our School Infection Survey (SIS) results today, I would like to reiterate what we have learnt about #COVID19 after 9 million students returned to full-time in-person education in England in March this year 👇
2/ The UK went into national lockdown including school closures in Jan 2021 following emergence of the Alpha variant. #COVID19 cases declined rapidly & schools reopened fully on 08 Mar 2021 (wk 10) when the rest of England remained in lockdown 👉 gov.uk/government/sta…
3/ During the 3 weeks until Easter holidays (wks 10-13, black circle), we saw a small ⬆️ in #covid19 cases among primary school kids (red line) & (because of mass rapid antigen testing before schools reopening) a large short-lived spike in secondary school kids (green) 👇
Read 11 tweets
9 Aug
1/ There have been increasing claims, mainly in North American news outlets, that the #SARSCoV2 DELTA variant is causing more severe #COVID19 in kids compared to previous variants

Well, everything we know so far indicates that’s it’s *not* true. Here’s why…🧵
2/ It’s true that the delta variant is more transmissible the both the alpha variant & the original strains, which means that it will infect more people more quickly, but there is no evidence that the risk of infection or transmission to others is different in kids vs adults
3/ Because of its higher transmissibility, there will be more Delta variant cases &, since most adults in many countries are vaccinated against #COVID19, cases/hospitalisations may seem disproportionately ⬆️ in kids (especially teens) vs adults. This just shows that #VaccinesWork
Read 13 tweets
7 Aug
1/ It’s actually headline-grabbing news articles such as this that fuel conspiracy theories

The JCVI did not make a U-turn on vaccinating teens. The JCVI path to vaccinating teens has remained the same & their message has been consistent. Here’s why 🧵

2/ On 19 July 2021, JCVI issued advice on COVID-19 vaccination for teenagers

JCVI advised that those aged 12+ years with specific underlying health conditions that put them at risk of serious COVID-19 should be offered COVID-19 vaccination

👉 gov.uk/government/pub…
3/ For healthy teens, however, JCVI *deferred* the decision, specifically stating “Data on the incidence of these events [myocarditis in teens & young adults] are currently limited, & the longer-term health effects from the myocarditis events reported are not yet well understood”
Read 10 tweets
31 Jul
1/ Our preprint on #SARSCoV2 infection & transmission in secondary schools following the emergence of the Alpha variant in England is now online

We took multiple blood samples from ~2,000 students/staff for #SARSCoV2 antibodies. Here’s what we found 🧵

2/ In England, #Covid19 cases due to the Alpha variant increased rapidly from late Nov 2020, leading to national lockdown in Dec 2020, including school closures. When schools reopened fully in Mar 2021, we took blood samples from 1,895 students & staff in our sKIDsPLUS study
3/ Between December 2020 & March 2021, 5.6% (61/1094) students & 4.4% (35/792) staff had laboratory-confirmed SARS-CoV-2 infection.

Most of these infections were acquired during community peaks in infections rates in December 2020, with a trickle of cases throughout lockdown
Read 8 tweets
29 Jul
1/ It was the JCVI that used basic immunological principles of vaccination to recommend a 12-week interval between #COVID19 vaccines to save more lives during the Alpha wave in the UK

Our paper (preprint) here shows why that was the right decision…🧵

2/ We tested #SARSCoV2 antibodies in adults aged 50-89 years and found that, for both Pfizer & AZ vaccines, 95% had seroconverted (developed antibodies) by 35-55 days after the first #COVID19 dose, and 100% by 7+ days after the second dose

👉 medrxiv.org/content/10.110…
3/ BUT, when the vaccines were given 9-11 weeks apart, antibody levels at 2-5 weeks after 2nd dose were 6x ⬆️ for Pfizer (6703; 95%CI, 5887-7633) than AZ (1093; 806-1483), which in turn were higher than Pfizer given 3-4 weeks apart (694; 540 - 893) 👉medrxiv.org/content/10.110…
Read 6 tweets

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