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Paxlovid remains effective in those vaccinated against COVID-19

4th July 2022

Israeli researchers have found that paxlovid use in those at risk of COVID-19 progression remains effective even in fully vaccinated patients

The effectiveness of the anti-viral drug paxlovid in preventing the progression of COVID-19 remains even in those who have been adequately vaccinated against the virus according to the results of a real-world study by Israeli researchers.

Paxlovid consists of nirmatrelivir, a protease inhibitor against COVID-19 and ritonavir, which reduces the in vivo metabolism of nirmatrelivir. The published data for the drug (the EPIC-HR trial) suggested that treatment of symptomatic COVID-19 in patients at risk of progression to severe disease, results in an 89% lower risk compared to placebo. Nevertheless, the study was undertaken before omicron became the main circulating variant and therefore the generalisability of the study’s findings are potentially limited. Consequently, for the present study, the Israeli team decided to undertake a large, retrospective cohort study of high-risk COVID-19 patients, to assess the effectiveness of paxlovid at preventing progression to severe COVID-19 and subsequent death during the time when omicron was the predominant strain.

Using a large, national health service database, the researchers identified all adults (18 years and over) who tested positive for COVID-19 but restricted the search to those who would be suitable candidates for treatment with paxlovid, i.e., those who were older than 60 years, with a body mass index (BMI) greater than 30 and with co-morbidities including diabetes, hypertension and cardiovascular disease. However, unlike in the EPIC-HR trial, where those who had been vaccinated were excluded, for the present analysis, researchers included patients, regardless of their vaccination status. The main outcome of the study was a composite of severe COVID-19 or COVID-19-related mortality. For their analysis, the researchers included demographic and co-morbidity data and which were adjusted for in the analysis.

Paxlovid and progression of COVID-19

A total of 4,737 individuals with a mean age of 68.5 years (42.1% male) were treated with paxlovid and compared with 175,614 individuals who tested positive but who did not receive the drug. In total, 77.8% of those given paxlovid had adequate COVID-19 vaccination compared to 75% of those in the non-paxlovid group.

Overall, the primary outcome occurred in 39 individuals receiving paxlovid compared to 903 in those not given the drug. Paxlovid was therefore associated with a significantly lower risk of severe COVID-19 or mortality (hazard ratio, HR = 0.54, 95% CI 0.39 – 0.75). Moreover, among the whole cohort, having adequate COVID-19 vaccination, was also associated with a significantly lower risk of the primary outcome (HR = 0.20, 95% CI 0.17 – 0.22).

When the analysis was restricted to those diagnosed with COVID-19 when omicron was the main circulating variant, paxlovid was also associated with a greater reduction in the primary endpoint (HR = 0.43, 95% CI 0.64 – 0.85). Interestingly, among those given paxlovid and who were adequately vaccinated, there was still a significant reduction in the primary outcome (HR = 0.62, 95% CI 0.39 – 0.98) as well as among those not vaccinated (HR = 0.52, 95% CI 0.32 – 0.82).

The authors concluded that their study had demonstrated that in a real-world setting and during the period of time when omicron was the dominant variant, paxlovid was associated with a significant reduction in progression of COVID-19 and COVID-19-related mortality.

Najjar-Debbiny R et al. Effectiveness of Paxlovid in Reducing Severe COVID-19 and Mortality in High Risk Patients Clin Infect Dis 2022

Stopping methotrexate for 2 weeks after COVID-19 vaccination boosts immune response

30th June 2022

Halting methotrexate for two weeks after a COVID-19 vaccination boosted the level of antibodies generated compared with continued drug use

Stopping methotrexate (MTX) for two weeks after a third COVID-19 vaccination significantly enhanced the level of antibodies produced compared to continuing with the drug, according to the results of a randomised trial by a team of UK researchers.

The use of the immunomodulatory drug methotrexate, is known to adversely affect the humoral and cellular immune response to COVID-19 mRNA vaccines. In fact, studies have shown that seroconversion rates after COVID-19 vaccination are significantly lower in immunocompromised patients, especially organ transplant recipients. As a result, it is important to implement strategies that can enable those who are immunocompromised to mount a satisfactory immune response. It has been shown that discontinuation of immunosuppressant drugs such as methotrexate in patients with rheumatoid arthritis, for either 4 weeks before, 2 weeks before and for 2 weeks after vaccination, improves the immunogenicity of seasonal influenza vaccination. In fact, the highest immune response occurred when MTX was discontinued two weeks after vaccination and this effect was confirmed in another study that specifically focused on stopping the drug two weeks after seasonal influenza vaccination.

Since the effectiveness of this approach has not been formally evaluated for the COVID-19 vaccine, for the present study, the UK undertook a randomised trial among immunocompromised patients prescribed methotrexate. The Vaccine Response On/Off Methotrexate (VROOM) trial, randomised participants 1:1 to either suspension of MTX (suspend methotrexate) for two weeks immediately after their COVID-19 booster dose, or to continue with the drug as usual (continue methotrexate). Individuals were recruited from both rheumatology and dermatology clinics and who had been taking low dose MTX (< 25 mg/week) for at least 3 months. In addition, the researchers only enrolled participants who had previously received two COVID-19 vaccine doses. The primary outcome of the study was the antibody response against the receptor-binding domain of the COVID-19 spike protein (S1-RBD) 4 weeks after receipt of the third COVID-19 vaccine dose. Secondary outcomes included S1-RBD antibody titres at 12 weeks post-vaccination and self-reported levels of disease activity.

Methotrexate suspension and S1-RBD antibody response

A total of 254 individuals with a mean age of 59.1 years (61% female) were included in the trial and randomised equally to either strategy. Overall, 51% of participants had rheumatoid arthritis, 34% psoriasis and 20% a skin condition alone. The median dose of methotrexate taken as 20 mg/week.

After 4 weeks, the geometric mean SI-RBD antibody titre was 22,750 U/ml in the suspend methotrexate group and 10,798 U/ml in the continue methotrexate group (p < 0.0001). This increase was independent of the dose and administration route of methotrexate, as well as type of immune-mediated inflammatory disease and age. Moreover, this difference in response remained significant at week 12 (16,520 vs 8094).

One downside of the study was that significantly more patients in the suspend methotrexate group self-reported at least one disease flare over the 12 week period compared to those who continued with the drug (71% vs 45%, odds ratio, OR = 2.83, 95% CI 1.64 – 4.88). However, these flares were generally self-managed and without any major impacts on quality of life.

The authors concluded that their strategy of stopping MTX was both safe and boosted the level of COVID-19 antibodies and called for further studies to examine the effect of stopping other immunosuppressant drugs on the level of antibody response.

Abhishek A et al. Effect of a 2-week interruption in methotrexate treatment versus continued treatment on COVID-19 booster vaccine immunity in adults with inflammatory conditions (VROOM study): a randomised, open label, superiority trial. Lancet Resp Med 2022

Fourth COVID-19 vaccination superior to third against adverse COVID-19-related outcomes

29th April 2022

A fourth COVID-19 vaccination offers greater protection against adverse COVID-19 outcomes compared to individuals having had only three doses

Having a fourth COVID-19 vaccination at least four months after the third dose, offers better short-term protection against COVID-19-related adverse outcomes compared to only three doses of the vaccine. This was the main finding of a study by Israeli researchers from the Clalit Research Institute, Innovation Division, Tel-Aviv, Isreal.

Whilst millions of individuals have now received at least three doses of a COVID-19 vaccine, there is evidence that with the emergence of variants such as Omicron, vaccine effectiveness wanes over time. This was observed, for example, in one US study, during the Omicron period. The authors found that vaccine effectiveness against emergency department visits was 87% during the first 2 months after a third dose but decreased to 66% among those vaccinated 4-5 months earlier. In fact, it is already apparent, albeit from a single study, that the rates of confirmed COVID-19 infection and severe illness were lower after a fourth dose of BNT162b2 vaccine compared to after only three doses. Whilst this is an important finding, to date, the effectiveness of a fourth COVID-19 vaccination against other outcomes of interest such as hospitalisation and deaths remains uncertain.

For the present study the Israeli team examined the relative effectiveness of four compared to three doses of vaccine among those aged 60 years and older who had received a third dose at least 4 months earlier.

Using data contained within the Clalit Health Services, which is the largest payer-provide organisation in Israel, the team included patients deemed eligible for a fourth dose and who had no previously recorded infection with COVID-19. There were a total of 5 outcomes of interest: COVID-19 infection; symptomatic COVID-19, COVID-19-related hospitalisation, severe COVID-19 and COVID-19-related death. All of these outcomes were assessed 7 to 30 days after the fourth COVID-19 vaccination and 14 to 30 days after vaccination. Those who received a fourth vaccine dose were matched with individuals who had only received three doses and with similar co-morbidities.

Fourth COVID-19 vaccination and adverse COVID-19-related outcomes

A total of 182,122 individuals who received a fourth vaccination dose and a median age of 72 years (53% female) were matched with a group of control patients (three vaccine doses).

During days 7 to 30, the estimated relative effectiveness of the fourth COVID-19 vaccination compared to three doses was 45% against a PCR confirmed COVID-19 infection, 55% against symptomatic COVID-19, 68% against COVID-19 hospitalisation and 74% against COVID-19-related mortality. Moreover, these effectiveness values were broadly similar when assessed 14 to 30 days after the fourth dose.

The authors discussed how use of a fourth dose appeared to be effective against the Omicron variant which was the main circulating variant at the time of the study (January 3 to February 18, 2022). They concluded that a fourth COVID-19 vaccination dose provided additional protection compared to only three doses in those older than 60 years of age.

Magen O et al. Fourth Dose of BNT162b2 mRNA Covid-19 Vaccine in a Nationwide Setting New Eng J Med 2022

Seroconversion rates low after COVID-19 vaccination among immunocompromised

18th March 2022

Seroconversion rates among immunocompromised patients are low after the first COVID-19 vaccine dose but increase upon receipt of the second

Seroconversion rates after a single COVID-19 vaccination among immunocompromised patients is low but improves after a second dose according to the findings of a systematic review and meta-analysis by researchers from the Yong Loo Lin School of Medicine, National University of Singapore, Singapore.

Immunocompromised patients are at an increased risk severe COVID-19 illness and death. Moreover, it is recognised that among immunocompromised, solid organ transplant patients, a wide range of respiratory viruses cause significant morbidity and mortality among transplant recipients. In a 2020 review of COVID-19 in cancer patients, it was noted how those with cancer are susceptible to severe clinically adverse events and a higher mortality from COVID-19 infection as well as morbidity and mortality from their underlying malignancy. Although one 2018 systematic review found that  seroconversion and sero-protection rates for influenza antigens were low in solid organ transplant recipients, no such reviews on the immunogenicity of COVID-19 vaccines and the overall seroconversion rates among cohorts of immunocompromised patients and been undertaken.

For the present study, the Singaporean team compared the seroconversion rates among groups of immunocompromised patients compared to immunocompetent controls. The team searched for studies that included patients with active cancer of solid organs, haematological cancers, organ transplant recipients, those with active immune mediated inflammatory disorders and for which a comparator group was included. The primary outcomes of interest were seroconversion after the first and second COVID-19 vaccine doses.

Seroconversion rates after vaccination

A total of 82 studies were included in the meta-analysis.

Among those with haematological cancers, compared to immunocompetent individuals, the seroconversion rate after the first vaccination was less than half (risk ratio, RR = 0.40, 95% CI 0.32 – 0.50) and similar for those with solid cancers (RR = 0.55, 95% CI 0.46 – 0.65) and immune mediated inflammatory disorders (RR = 0.53, 95% CI 0.39 – 0.71). However, it was significantly lower for organ transplant patients (RR = 0.06, 95% CI 0.04 – 0.09).

After the second vaccination, the rates of seroconversion increased. For example, for haematological cancers (RR = 0.63) and among those with solid cancer (RR = 0.90) and whilst higher, remained very low, among organ transplant patients (RR = 0.39).

The authors did not include studies where a third COVID-19 dose had been administered in the meta-analysis because most studies did not include a comparator for control purposes. Nevertheless, based solely on a systematic review, they found that conversion rates for organ transplant patients improved by 36 and 66.7%.

The authors concluded that administration of a third vaccine dose (which has now become standard practice for everyone) is warranted for immunocompromised patients.

Lee ARYB et al. Efficacy of covid-19 vaccines in immunocompromised patients: systematic review and meta-analysis BMJ 2022

Booster COVID-19 vaccination improves immune response in cancer patients undergoing treatment

21st January 2022

A booster COVID-19 dose administered to cancer patients on active treatment leads to an improved immune response in those fully vaccinated

A booster COVID-19 dose to cancer patients with solid tumours in receipt of active treatment, improves their immune response, according to the results of a study by a team from the University Paris Est Créteil, Paris, France.

Since the start of the COVID-19 pandemic, cancer patients have been deemed to be at high risk and thus a priority group for access to available vaccines. Nevertheless, as cancer patients were excluded from the vaccine efficacy trials, the nature and level of the immunogenic response to vaccination among cancer patients was uncertain. Data from a study among cancer patients on treatment has shown that after a first dose, 29% of patients were seropositive and that this rate increased to 86% after the second dose. But there appears to be only one study in patients with cancer who have received a third dose of vaccine and which appeared to show greater immunogenicity.

For the present study, the French team wanted to evaluate the immunogenicity of two and three doses of a COVID-19 vaccine in cancer patients currently receiving chemotherapy and how this was affected by the type of oncology treatment and the timing of vaccination. Using a prospective, observational design, the team included patients with solid organ active cancer, which they defined as ‘histologic confirmation of solid cancer under treatment within the previous 6 weeks or starting treatment during the next 2 weeks.’ The researchers collected information on the patient’s cancer diagnosis, therapy and cancer stages. All patients had received two doses of BNT162b2 on days 0 and 21 and those who had a prior history of COVID-19 infection or evidence of antibodies before vaccination were excluded. A booster COVID-19 (i.e., third) dose was offered to all of those who had a weak humoral response one month after the second dose, which was defined by an anti-spike protein antibody level below 1000 units.


In total, 163 patients with a median age of 66 years (53% male) were included in the analysis. The most common form of treatment was chemotherapy (75%), followed by targeted therapy (16%) and immunotherapy (9%).

One month after the first vaccine, only 15% of patients had anti-spike antibody titres > 1000, although one month after the second dose, this proportion increased to 65%. A booster COVID-19 dose was offered to 36 patients whose antibody level remained below 1000 units, one month after the second dose. This resulted in 75% of these patients, achieving antibody levels > 1000, one month after their third dose.

In their analysis, age, sex, cancer type, lymphopenia and use of corticosteroids four or more weeks before vaccination, were not associated with the level of immune response at the time of the second dose or even 28 days after the second dose. However, patients receiving either chemotherapy or targeted therapy had a lower anti-spike level than those given immunotherapy (odds ratio, OR = 5.4, 95% CI 1.5 – 20.2, p = 0.02). Other factors such as the time between vaccination and intravenous chemotherapy administration were also not associated with the intensity of the humoral response.

The authors concluded that a booster COVID-19 dose among those with solid tumours and in receipt of treatment, improved the immune response, highlighting the importance of a third dose in this patient cohort.


Fenioux C et al. SARS-CoV-2 Antibody Response to 2 or 3 Doses of the BNT162b2 Vaccine in Patients Treated With Anticancer Agents JAMA Oncol 2022

Vaccination leads to smaller reduction in transmission of delta compared to alpha COVID-19 variants

13th January 2022

Vaccination against COVID-19 leads to a higher level of transmission for the delta compared to the alpha variant

Vaccination has been found to result in a smaller reduction in the transmission of the Delta compared to the alpha variant according to a study by researchers from Oxford University, UK.

Vaccination against COVID-19 has been shown to reduce symptomatic infection and even onward transmission of the virus among household contacts. Furthermore, some data indicates that this reduced risk of onward transmission is because of a lower viral load among vaccinated individuals although other evidence points to a similar viral load among those who are vaccinated but infected with the Delta variant.

For the present study, the Oxford team used national contact testing data in England for adults (> 18 yeas of age) with both symptomatic and asymptomatic infections. Their analysis included vaccination with either BNT162b2 or ChAdOx1 to investigate differences in transmission from index patients infected with either variant. The analysis included regression models to determine any associations between onward transmission and the vaccination status of the index patient.


Among 146,243 tested contacts from a total of 108,498 index patients, with a median age of 34 years (51% female), 37% had a positive PCR test.

Using regression modelling, among index patients doubly vaccinated with BNT162b2 and who became infected, there was a significantly reduced risk of onward transmission of the Alpha variant (adjusted rate ratio, aRR = 0.32, 95% CI 0.21 – 0.48) compared unvaccinated individuals. Similarly, those with two vaccinations of ChAdOx1, also had a reduced risk of onward transmission (aRR = 0.48, 95% CI 0.30 – 0.78) compared to the unvaccinated.

In contrast, the extent of onward transmission of the Delta variant was reduced compared to Alpha by both vaccines but was greater among those doubly vaccinated with BNT162b2 (aRR = 0.50, 95% CI 0.39 – 0.65) compared to ChAdOx1 (aRR = 0.76, 95% 0.70 – 0.82). In other words, index patients vaccinated with BNT162b2 were less likely to have contacts with a positive PCR test for Delta compared to those given the ChAdOx1 vaccine.

The Delta variant was also associated with more onward transmission from both symptomatic index patients (aRR = 1.24, 95% CI 1.12 – 1.38) and from asymptomatic individuals (aRR = 1.40, 95% CI 1.22 – 1.59) and this was independent of both index and contact vaccination status.

Interestingly, the risk of infection with the Alpha variant among fully vaccinated contacts, was much lower among those given BNT162b2 (aRR = 0.15, 95% CI 0.11 – 021) compared to those fully vaccinated with ChAdOx1 (aRR = 0.40, 95% CI 0.27 – 0.59) and the magnitude of these reductions were similar for infections with the Delta variant.

Both symptomatic and asymptomatic index patients infected with the Delta variant had lower Ct values (i.e., higher viral loads) compared to those infected with the Alpha variant. When including Ct values in their regression models, the authors reported that lower Ct values were independently associated with increased transmission of either variant.

The authors concluded that vaccination was associated with a smaller reduction in transmission of the Delta compared to the Alpha variant.


Eyre DW wt al. Effect of Covid-19 Vaccination on Transmission of Alpha and Delta Variants. N Eng J Med 2022

Subclinical axillary lymphadenopathy due to COVID-19 vaccine seen on mammograms

10th December 2021

Subclinical axillary lymphadenopathy seen on mammography suggests scans are done before or several weeks after COVID-19 vaccination

The presence of subclinical axillary lymphadenopathy (sLAD) on mammography was significantly more likely among women who had received a COVID-19 vaccination, indicating that they should either delay screening or schedule visits before vaccination. This was the finding of a retrospective study by a team from the Baylor University Medical Center, Dallas, USA.

The term lymphadenopathy refers to lymph nodes that are abnormal in size and axillary lymphadenopathy, describes changes in the size and consistency of lymph nodes in the armpit. There are several potential causes of unilateral axillary lymphadenopathy including breast cancer and which therefore warrants further diagnostic investigations if these changes are observed during screening. Although the presence of sLAD has been observed in women who have received a COVID-19 vaccination, what remains uncertain, is the proportion of vaccinated women that will develop these lesions after either the Pfizer or Moderna vaccines.

Based on case reports of sLAD in vaccinated women, for the present study, the authors investigated the prevalence of the condition in all women who had attended a breast screening programme since December 2020 until April 2021. Data from medical records included the woman’s vaccination status, the vaccine received and the presence or absence of sLAD on mammography. The researchers cross-referenced prior imaging for all women to ensure that there was no baseline evidence of an axillary lymphadenopathy and excluded women who had presented for diagnostic mammography for a palpable axillary lump or pain and those with a history of breast cancer.


In total, 1027 women with a mean age range of 56.4 to 63.7 years were included in the analysis. There were 158 who received the Moderna vaccine, 144 (Pfizer) and 725 who had not been vaccinated. From these 1027 women, 43 (4.2%) had an sLAD; 3.3% of those who had been vaccinated compared to 0.9% who were unvaccinated and this difference was statistically significant (p < 0.01).

When comparing the two vaccines, the incidence of unilateral axillary lymphadenopathy was higher among those who received the Pfizer vaccination (13.2% vs 9.5%, Pfizer vs Moderna). Among the 43 women with sLAD and who were recalled after screening, vaccine induced sLAD was more likely to have resolved when re-scanned an average of 46.5 days since their COVID-19 vaccination.

The authors concluded that women who have received a COVID-19 vaccination within 8 weeks of their screening mammogram, were significantly more likely to present with a subclinical axillary lymphadenopathy and that this could result in unnecessary further diagnostic workload. They suggested that providers should either delay screening mammograms by 8 weeks in patients who have been vaccinated or that screening should be undertaken before vaccination to avoid unnecessary follow-up.


Raj S et al. COVID-19 vaccine-associated subclinical axillary lymphadenopathy on screening mammogram Acad Radiol 2021

mRNA-1273 vaccine associated with lower risk of COVID-19 outcomes than BNT162b

8th December 2021

mRNA-1273 appears to be associated with a lower risk of COVID-19-related outcomes such as infection, hospitalisation and death compared to BNT162b. This was the finding of the first head-to-head vaccine effectiveness analysis undertaken by a group of researchers from the Brigham and Women’s Hospital, Harvard Medical School, Boston, US.

Randomised controlled trials have already demonstrated the effectiveness of the currently available COVID-19 vaccines. For instance, the mRNA-1273 vaccine (Moderna) has an efficacy of 94.1% at preventing COVID-19 illness and that a similar efficacy (95%) has been observed for BNT162b (Pfizer-BioNTech).

However, despite this near identical level of efficacy, other work has suggested that there might be differences between these two vaccines, even though they have the same mode of action. One study, for example, indicated that the mRNA-1273 vaccine produced a higher humoral immunogenicity than BNT162b, while other data show that the Moderna vaccine it is associated with a two-fold reduced risk of breakthrough infections compared to BNT162b and also results in a lower incidence of COVID-19-related hospitalisations.

For the present study, the US team turned to data from the national healthcare databases of the Department of Veterans Affairs, which is the largest US integrated healthcare system. The researchers sought to compare the relative effectiveness of the Moderna and Pfizer-BioNTech vaccines with respect to documented COVID-19 infections, symptomatic COVID-19, hospitalisation, admission to an intensive care unit (ICU) and death. In addition, the team examined the effectiveness of the two vaccines against the delta COVID-19 variant and examined these outcomes after 24 weeks.


During the period of study, there were 367,113 recipients of the BN162b and 397,690 of the mRNA-1273 vaccines. Over a 24-week period, 2016 COVID-19 infections were documented, of which 559 were detected as symptomatic, 411 which led to hospitalisation, 125 ICU admissions and 81 deaths.

The absolute risk of infection was low in both vaccine groups; 5.75 events per 1000 persons with the Pfizer-BioNTech and 4.52 with the Moderna vaccine. The 24 week risk ratio for infections for BNT162b compared to mRAN-1273 was 1.27 (95% CI 1.15 – 1.42), 1.39 for symptomatic infection, 1.70 for hospitalisation, 1.38 for ICU admission and 1.11 for death. Each of these risks was statistically significant apart from the risk of death. The overall risk difference expressed as events over 24 weeks per 1,000 persons was 1.23 for a documented infection.

Using these data, the authors calculated the number needed to vaccinate with mRNA-1273 instead of BN162b to prevent one case of documented infection was 813.

Analysis during the time period characterised by dominance of the delta COVID-19 variant, there was a 58% higher risk of infection in those vaccinated with BNT162b although this difference was non-significant (risk ratio = 1.58, 95% CI 0.85 – 2.33).

Commenting on these findings, the authors highlighted how their study had shown that recipients of the BNT162b vaccine had a 27% higher risk of a documented COVID-19 infection and a 70% increased risk of hospitalisation compared to the Moderna vaccine.

They concluded that the data provided evidence of a lower 24-week risk of COVID-19-related outcomes among those receiving the m-RNA-1273 vaccine compared to BNT162b.


Dickerman BA et al. Comparative Effectiveness of BNT162b2 and mRNA-1273 Vaccines in U.S. Veterans. New Eng J Med 2021

Comirnaty COVID-19 booster shows greater than 90% effectiveness in over 50s

6th December 2021

A Comirnaty booster dose given to those aged 50 years and over provides >90% vaccine effectiveness against COVID-19 infection

A Comirnaty booster dose in those over the age of 50 provides a greater than 90% vaccine effectiveness, irrespective of whether individuals had been previously fully vaccinated with ChAdOx1-S (AstraZeneca) or Comirnaty (BNT162b). This was the finding of a study by a team from the UK Health Security Agency, UK, which is available online but not published in a peer-reviewed journal.

With evidence that the efficacy of COVID-19 vaccines wanes 20 weeks after vaccination, the Joint Committee on Vaccination and Immunisation (JCVI) in the UK issued a statement highlighting the need for a booster dose of COVID-19 vaccines in an effort to combat the virus during the winter months. Moreover, after a review of the available data on booster responses, the JCVI advised a preference for the Comirnaty vaccine as the booster dose irrespective of which product was used to provide the initial full vaccination.

In the present study, the UK team sought to estimate the real-world effectiveness of a single Comirnaty booster dose in those aged 50 years and older. The researchers compared vaccination status in this patient cohort, who were symptomatic for COVID-19 and with a positive PCR test result. Data was obtained from the National Immunisation Management System (NIMS) and a booster dose was defined as one given 140 days or more after a second vaccination dose. Vaccine effectiveness was adjusted in regression models for age, deprivation, ethnicity, care home residence status and co-morbidities. The analysis was also stratified by the primary vaccination received, i.e., either ChAdOx1-S (AstraZeneca) or Comirnaty and vaccine effectiveness assessed at several time points e.g., 2 to 6 days post booster dose and 14 or more days later.

For the primary analysis, the team compared vaccine effectiveness in those who received a booster with those who had been fully vaccinated but without a booster dose. In a secondary analysis, they determined the absolute vaccine effectiveness which was the difference in rates of infection between those who had two doses (at least 140 days apart) and a booster with those who were unvaccinated.


There were 271,747 eligible tests in people 50 years and older, of which 13,568 (5%) were unvaccinated with the remainder being fully vaccinated with either ChAdOx1-S or comirnaty (BNT162b)

The vaccine effectiveness from a BNT162b booster in those who were fully vaccinated with ChAdOx1-S was 87.4% (95% CI 84.9 – 89.4) and 84.4% (95% CI 82.8 – 85.8%) in those fully vaccinated with BNT162b.

In the secondary analysis, compared with unvaccinated individuals, those fully vaccinated with a primary course of ChAdOx1-S had an absolute vaccine effectiveness of 93.1% (95% CI 91.7 – 94.3%) and 94% (95% CI 93.4 – 94.6%) in those fully vaccinated with BNT162b.

Interestingly, when compared with those who were fully vaccinated but had not received a booster dose, the vaccine effectiveness after 20 or more weeks was 44.1% for the ChAdOx1-S vaccine and 62.5% for BNT162b.

In their conclusion, the authors wrote ‘our study provides real world evidence of significant increased protection from the booster dose against symptomatic disease in those aged over 50 years of age irrespective of which primary course was received.’


Andrews N et al. Effectiveness of BNT162b2 (Comirnaty, PfizerBioNTech) COVID-19 booster vaccine against
COVID-19 related symptoms in England: test negative case-control study

Comirnaty COVID-19 vaccine approved by EMA for children aged 5 – 11

30th November 2021

Comirnaty has now been granted a license extension and approved by the EMA for COVID-19 vaccination in children aged 5 to 11 years of age

Comirnaty is the COVID-19 vaccine made by Pfizer-BioNTech and has now been approved by the EMA for use in children aged between 5 and 11 years of age given as two doses, three weeks apart. The vaccine was previously approved for use in adults and children from the age of 12.

Although a study published in Nature Medicine in November 2021, reported that the majority of children and young people infected with COVID-19 survive, the analysis was based on the wild-type and alpha variant only. However, more recent data from the US, shows that once the delta variant became the dominant COVID-19 strain in circulation, weekly COVID-19–associated hospitalisation rates among children and adolescents rose nearly five-fold during late June–mid-August 2021.

Based on these findings, the Centers for Disease Control in the US considered that ‘preventive measures to reduce transmission and severe outcomes in children and adolescents are critical, including vaccination, universal masking in schools, and masking by persons aged ≥2 years in other indoor public spaces and child care centers.’

Clinical efficacy in younger children

The EMA approval of comirnaty in children from the age of 5 was based on a single study of the vaccine in those aged 5 to 11 years. The study itself was undertaken in two stages; an initial phase 1 dosing-finding trial, in which a total of 48 children 5 to 11 years of age, received two 10-μg doses of BNT162b2 administered 21 days apart (which was a third of the dose given for 12 to 15 year olds), after which, the participants were randomised in a 2:1 ratio and given two 10 μg doses BNT162b2 or saline placebo.

The study examined the immunogenicity of the 10-μg dose but also the vaccine efficacy against confirmed COVID-19 infection which had an onset at least 7 days after the second dose. For the phase 2 arm of the study, 2268 children with a mean age of 8.2 years (52.1% male) were randomised to BNT162b2 or placebo. The immunogenicity showed a similar geometric mean ratio to that achieved from a 30-μg dose given to older children.

In terms of vaccine efficacy, there were three cases of COVID-19, with an onset 7 or more days after the second vaccination dose in the BNT162b2 group and 16 among placebo recipients, giving a vaccine efficacy of 90.7% (95% CI, 67.7 to 98.3). 

While the EMA has approved comirnaty in younger children, this has not occurred in the UK, with the MHRA only approving vaccination for those aged 12 – 15 years.

Source. EMA News 25th November 2021