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Emergency care rarely needed for breakthrough COVID-19 infections

17th September 2021

A study of breakthrough COVID-19 infections found that less than 1% of all emergency care visits occurred in those fully vaccinated.

The efficacy of currently available COVID-19 vaccines, such as BNT162b, has been clearly demonstrated in clinical trials. Nevertheless, because vaccines are not 100% effective, there are likely to be individuals who experience a breakthrough COVID-19 infection. However, what is less clear is the extent to which these breakthrough infections result in either emergency care (EC) visits or even hospital admission.

In trying to better understand this question, a team from the Department of Emergency Medicine, Beaumont Hospital, Michigan, US, performed an observational cohort analysis comparing the need for EC among those with confirmed COVID-19 infection. The team compared the outcomes for adult patients who were either unvaccinated (UV), partially vaccinated (PV) or fully vaccinated (FV). For the purposes of the study, FV individuals were defined as those who had a positive COVID-19 test result and symptom onset < 14 days after their second vaccination. The team used electronic health records to confirm COVID-19 infection status and collect demographic and clinical data such as co-morbidities. The primary outcome measure was the rate of emergency care/hospitalisation encounters in those testing positive among the three groups. This was defined as the number of newly presenting hospital-based COVID-19 encounters divided by the state population within each respective vaccination group and expressed as a rate per 100,000 visits. The team also calculated weekly rates of COVID-19 EC encounters for each group. Secondary outcomes included severe disease represented as a composite outcome (intensive care admission, mechanical ventilation or in-hospital death), length of hospital stay.

There was a total of 11,834 EC visits which met the inclusion criteria. Patients had an overall mean age of 53 years (47.2% male) of whom 10,880 (91.9%) were UV, 825 (7%) PV and 129 (1.1%) FV. In terms of the weekly rate of COVID-19 EC encounters, the rate of breakthrough COVID-19 infections among FV individuals was 96% lower compared with the UV group. COVID-19 EC visits peaked at 22.61, 12.88 and 1.29 visits per 100,000 for those who were UV, PV and FV respectively.

The composite secondary outcome of severe disease occurred in 6.8% of the UV, 10.3% of the PV and 12.4% of the FV group. While those who were FV had a lower risk of severe disease compared to the UV group, this difference was not significant (hazard ratio, HR = 0.84, 95% CI 0.52–1.38) and the mean age of those with severe disease was 74.1 years. Among the PV group, the risk was either higher or lower (HR = 1.03, 95% CI 0.78–1.35).

The authors concluded that while breakthrough COVID-19 infections occurred in fully vaccinated individuals, these were rare, accounting for only 1% of all COVID-19-related EC visits. Nevertheless, when admission to hospital was required for those who were fully vaccinated, the risk of severe outcomes was similar to those who were unvaccinated.

Bahl A et al. Vaccination reduces need for emergency care in breakthrough COVID-19 infections: A multicenter cohort study. The Lancet Regional Health Americas 2021

Less than 1% of COVID-19 related deaths among fully vaccinated

14th September 2021

An analysis of all COVID-19-related deaths in England between the 2nd of January and July 2021, has been published by the Office for National Statistics (ONS). The data include a breakdown of all recorded deaths analysed by vaccination status. Clearly, a certain number of both infections and deaths among those who have been vaccinated, referred to as breakthrough infections, are likely to occur simply because the COVID-19 vaccines have been administered to many millions of people and none can be considered as 100 per cent effective.

The risk of becoming infected with COVID-19 is, according to the ONS infection survey, highest within the first 21 days after receipt of the primer vaccine dose. The bulletin from the ONS examines deaths in relation to vaccination status and uses age-standardised mortality rates, which adjusts for differences in the population age distribution.


There were a total of 640 deaths in those who had received two COVID-19 vaccines; 182 within 21 days of their second vaccine dose and 458, 21 days after their second dose. Together, both groups represent 1.2% of all COVID-19 related deaths although only 0.8% (458/51,281) of all deaths occurred 21 days after the second vaccine dose. In other words, less than 1% of all COVID-19 related deaths occurred in those who were fully vaccinated. However, it is worth noting that the more infectious delta variant only became the dominant strain, according to the ONS, since the end of May 2021 and hopefully future bulletins will report upon any associated mortality changes.

In cases where the date of infection was known, among those who had received two vaccinations, 47.5% became infected 14 or more days after the second dose, leading to 256 deaths.

Characteristics of individuals with breakthrough deaths

Among the 256 deaths occurring 14 or more days after infection, linked data, which provides demographic and clinical information was available for 252 individuals. The information showed that the average age of death among these fully vaccinated individuals was 84 years. Nearly two-thirds (61.1%) were male and 76.6% were described as clinically vulnerable and 13.1% of deaths occurred among immunocompromised patients.

The latest set of ONS data clearly shows that COVID-19 related deaths are significantly reduced due to vaccination but also serves as a reminder that deaths will still occur, especially among the clinically vulnerable and immunocompromised, highlighting the need for booster doses.


ONS Deaths involving COVID-19 by vaccination status, England: deaths occurring between 2 January and 2 July 2021

Higher risk of hospitalisation from delta COVID-19 variant

3rd September 2021

A study has suggested that among unvaccinated individuals, infection with the delta COVID-19 variant doubles the risk of hospitalisation.

The emergence of COVID-19 variants, in particular the delta COVID-19 variant, is a cause for concern, especially, given evidence of reduced effectiveness of vaccines against the variant. Nevertheless, despite this, other data has indicated that vaccination protects against hospitalisation in those infected with the delta variant.

In an attempt to better characterise the severity of infection caused by the delta COVID-19 variant, a team from Public Health England, examined the relative risk of both hospital emergency care attendance or admission following infection with the variant and the extent to which this was modified by vaccination. The team used individual-level data on those with laboratory-confirmed COVID-19 infection between March 29 and May 23, 2021 and with whole viral genomic sequencing of either the alpha or delta COVID-19 variants. The risk of hospital admission and attendance at emergency care were compared for patients with either variant and by vaccination status, over a maximum of 14 days from their positive COVID-19 test. The primary analysis was the risk of hospitalisation outcomes (i.e., either admission or attendance), based on hazard ratios (HR). The main secondary analysis was the HRs for the same hospital outcomes based on vaccination status, which was dichotomised as either unvaccinated or less than 21 days since the first vaccine dose or 21 or more days since the first dose. Results were adjusted for age, sex, area of residence (based on deprivation) and the presence of any international travel within 14 days of a positive test.

Over the period of the study, there were 43,338 cases included in the analysis with 8,682 infections with the delta COVID-19 variant and 34,656 with the alpha variant. In addition, the majority of patients in both groups (74%) were unvaccinated. The median age of those infected with the delta COVID-19 variant was 29 years (48.9% female) which was slightly lower than those with the alpha variant (median age 31 years, 51.7% female). The estimated risk for hospitalisation within 14 days was higher with the delta COVID-19 variant compared with the alpha variant (adjusted HR, aHR = 2.26, 95% CI 1.32 – 3.89). Similarly, there was an increased risk for hospital admission or emergency care attendance within 14 days of infection for the delta compared with the alpha variant (aHR = 1.45, 95% CI 1.08 – 1.95).

When the data were analysed in terms of vaccination status, among those who were either unvaccinated or who had been vaccinated less than 21 days before infection, the risk of hospital admission was also higher among individuals with the delta COVID-19 variant (aHR = 2.32, 95% CI 1.29 – 4.16) and in those 21 days after their first vaccine dose although there was less precision over this outcome due to the wide confidence intervals (aHR = 1.94, 95% CI 0.47 – 8.05). This increased risk was also evident for the combination of hospital admission or emergency care attendance (aHR = 1.58, 95% CI 0.69 – 3.61).
In discussing their findings, the authors recognised that their estimates of the impact of vaccination was imprecise and that further work was needed to confirm the impact of vaccination on breakthrough infections. They concluded that among unvaccinated individuals, infection with the delta COVID-19 variant, doubles the risk of hospital admission.

Twohig KA et al. Hospital admission and emergency care attendance risk for SARS-CoV-2 delta (B.1.617.2) compared with alpha (B.1.1.7) variants of concern: a cohort study. Lancet Infect Dis 2021.

Risk of long COVID halved after full vaccination

Data from the COVID symptom study shows that full vaccination leads to a reduced risk of continued symptoms (i.e., long COVID).

Full vaccination against COVID-19 has led to reductions in the proportion of patients experiencing severe disease requiring hospitalisation although despite full vaccination, breakthrough infections are known to occur. It is necessary therefore to both identify and protect individuals who might be at a greater risk of re-infection after full vaccination. However, little is known about the potential risk factors for re-infection and whether or not full vaccination might reduce the incidence of persistent symptoms or long COVID.

Using data collected from the COVID Symptom Study, which is a prospective, community-based study based on self-reported data, researchers analysed the results from two patient cohorts. The first group were those who tested positive for COVID-19 at least 14 days after their first vaccination, but before their second (case group 1) and those who tested positive at least 7 days after their second vaccination dose (case group 2). The team included two match-controlled control groups, which were those with a negative COVID-19 test result during the same time-frame for the case 1 and 2 cohorts. In order to analyse the disease profiles associated with an increased risk of re-infection, the researchers selected sub-cohorts from cases 1 and 2, who continued using the app for 14 consecutive days after testing positive and again matched these to individuals who also used the app for the same period after infection but who were unvaccinated with a positive COVID-19 test result. In the analysis of risk factors and post-vaccination infection, adjustments were made for age, body mass index and sex.

There were 1,240,009 users who reported a first vaccine dose and of whom, 6030 (0.5%) subsequently tested positive for COVID-19 (case group 1). This compared with 971,504 who had received full vaccination and of whom, 2370 (0.2%) tested positive (case 2). Both groups were equally matched, with a mean age of 50.2 years and were predominately female (62.5%).

In the risk factor analysis, frailty was significantly associated with post-vaccination infection in older adults (odds ratio, OR = 1.93, 95% CI 1.50 – 2.48, p < 0.0001) and among individuals from highly deprived areas, (OR = 1.11, 95% CI 1.01 – 1.23, p = 0.039). Additionally, in older adults who received only a single vaccination, kidney disease (OR = 1.95), heart disease (OR = 1.30) and lung disease (OR = 1.27) were all significantly associated with post-vaccination infection. Interestingly, there was a significant reduction in of the risk of symptoms persisting beyond 28 days (i.e., long COVID) among those who were fully vaccinated (OR = 0.51, 95% CI 0.32 – 0.82, p = 0.006).
Commenting on their findings, the authors suggested that the data appeared to indicate that among those who were fully vaccinated, the risk of continued symptoms or long COVID appeared to be reduced by half. They concluded however, that these findings potentially support a cautious relaxation of mitigation strategies such as social distancing given the factors associated with an increased risk of re-infection.

Antonelli M et al. Risk factors and disease profile of post-vaccination SARS-CoV-2 infection in UK users of the COVID Symptom Study app: a prospective, community-based, nested, case-control study. Lancet Infect Dis 2021

Risk of clotting disorders higher after COVID-19 than vaccination

27th August 2021

A study suggests that the risk of clotting disorders appears to be significantly higher with COVID-19 infection compared to vaccination.

Published studies reporting the appearance of the clotting disorders thrombocytopenia and thrombosis after vaccination with the COVID-19 vaccine, ChAdOx1 in several European countries is a cause for concern. Nevertheless, while it appears that these adverse effects are rare, some countries have limited the use of this particular vaccine. Trying to establish whether clotting disorders are caused entirely by exposure to a COVID-19 vaccine is hampered by the fact that such clotting disorders have also been observed as a result of infection with the virus. In trying to untangle this association and to provide some much-needed perspective, a group of researchers led by the Nuffield Department of Primary Health Care Sciences, University of Oxford, UK, have examined the link between COVID-19 vaccination and the risk of thrombocytopenia and thromboembolic events in England. The researchers used a self-control case series analysis (i.e., where the individual acts as their own control) with patients between December 2020 to April 2021. They assessed the risk of these adverse clotting disorders among those who were vaccinated with the two COVID-19 vaccines, ChAdOx1 and BNT162b and the incidence of thrombotic events among the same individuals who tested positive for COVID-19. Included participants were aged 16 years and over who had received their first dose of either ChAdOx1 or BNT162b. They used three composite primary outcomes; hospital admission or death associated with one of the clotting disorders, i.e., thrombocytopenia, venous thromboembolism and arterial thromboembolism.

There were 19,608,008 people who received the ChAdOx1 vaccine, 9,513,625 the BNT162b and a total of 1,758,095 who had a positive COVID-19 test. In addition, during the study period, 9,764 people were hospitalised because of thrombocytopenia and 52 of these individuals died. An increased risk of thrombocytopenia was observed 8 – 14 days after the ChAdOx1 vaccine (incidence rate ratio, IRR = 1.33, 95% CI 1.19 – 1.47) and also after 22 – 28 days (IIR = 1.26). However, the risk associated with a positive COVID-19 test after 8 – 14 days was much higher (IIR = 5.27, 95% CI 4.34 – 6.40) and after 22 – 28 days (IIR = 1.50). For venous thromboembolism after the ChAdOx1 vaccine at days 8 – 14, the IIR was 1.10 but again much higher after a positive COVID-19 test during the same time period (IIR – 13.86). For BNT162b, the risk of thrombocytopenia was also increased between days 8 – 14 but not significant (IIR = 1.02, 95% CI 0.89 – 1.17).
Using these results, the authors estimated the excess number of adverse clotting disorders per 10 million exposed to each vaccine compared to a positive COVID-19 test. With the ChAdOx1 vaccine, this amounted to 107 excess thrombocytopenia events and 66 excess thromboembolism events. In contrast, for a positive COVID-19 test result, the corresponding values were 934 excess thrombocytopenia events and 12,614 excess thromboembolism events.
The authors concluded that while adverse clotting events did occur after COCVID-19 vaccination, these events were significantly less than those associated with being infected with the virus.

Hippisley-Cox J et al. Risk of thrombocytopenia and thromboembolism after covid-19 vaccination and SARS-CoV-2 positive testing: self-controlled case series study. BMJ 2021

Full COVID-19 vaccination boosts antibody response in those with prior infection

16th August 2021

Among those with a prior infection, full COVID-19 vaccination boosts their antibody response even to variants of concern.

Vaccines against COVID-19 have been administered across the globe and have been shown to be efficacious at preventing COVID-19 illness. However, with the emergence of viral variants, some of which are able to escape neutralising antibodies, there is an increased risk of vaccine breakthrough infections. While it is possible to modify existing vaccines to ensure that they are effective against variants of concern, an alternative strategy is to provide individuals with a third, or booster vaccination dose. In fact, there is animal data to suggest that a booster dose increases antibody titres to at least one variant of concern although whether this strategy will be effective in humans remains uncertain. One way of studying the value of a booster dose, is to compare the antibody response generated after full vaccination among those with and without prior infection. This was the objective of a study by a team from the Wolfson Centre for Global Virus Research, University of Nottingham, UK. They used data from the PANTHER Study which is designed to track frontline healthcare workers. For the present study, the researchers were interested in any differences in the antibody response among fully vaccinated individuals, in those with or without a prior COVID-19 infection. Participants were split into two groups (prior or no prior infection) and blood samples taken for analysis of IgG antibody levels to the wild-type COVID-19 and against two variants of concern, B.1.351 and P1 after both their first and second doses of vaccine which were given 10 weeks apart.

The total cohort consisted of 45 individuals with a mean age of 47.5 years (80% female) and 20 with a prior infection, all of whom had received two doses of BNT162b. The level of antibodies among individuals with a prior infection were higher after a single vaccine dose compared to previously uninfected participants. Interestingly, after the second vaccine dose, there was a significantly increased antibody response, not just to the wild-type COVID-19, but to the two variants of concern among those who had a prior infection compared with uninfected individuals.

Commenting on these findings, the authors suggested that their data showed how repeated exposure to COVID-19, i.e., through a prior infection and two doses of a vaccine, increased the level of neutralising antibodies. In other words, a prior infection much like a booster dose. Furthermore, it was also apparent that this increased antigenic exposure appeared to broaden an individual’s antibody response by creating neutralising antibodies to the two variants of concern. If confirmed in future studies, these results would be of enormous importance. For instance, if repeated exposure not only enhanced but extended immunity against variants of concern, there is a very strong argument for giving individuals a further, third, booster vaccine dose, even if this is directed at the original spike protein, to combat any new variants likely to emerge in the future.

Urbanowicz RA et al. Two doses of the SARS-CoV-2 BNT162b2 vaccine enhances antibody responses to variants in individuals with prior SARS-CoV-2 infection. Sci Transl Med 2021

Clinical markers for vaccine-induced thrombocytopenia and thrombosis identified

13th August 2021

The identification of clinical markers for vaccine-induced immune thrombocytopenia and thrombosis may help to guide effective management.

One of the most commonly used COVID-19 vaccines is ChAdOx1 made by AstraZeneca and since rollout of the vaccine in the UK in January 2021, millions of doses have been administered around the world. The ChAdOx1 vaccine has been found to be safe and able to induce a satisfactory antibody response. Though it is generally accepted that no vaccine is completely free of adverse effects, concerns over vaccine-induced thrombocytopenia (VITT) associated with ChAdOx1 appeared in June 2021. In one of these reports, doctors identified five cases of venous thrombosis and thrombocytopenia, 7–10 days after patients had received their first dose of the vaccine and proposed that this was a rare vaccine-related immune response. Nevertheless, this was not an isolated finding and a second report identified clinical and laboratory findings in 11 patients who had developed either thrombosis or thrombocytopenia, again 5–16 days after receipt of their first vaccine. Moreover, a common feature of both these reports was how in all cases, patients were previously fit and heathy. This adverse effect has been termed vaccine-induced thrombocytopenia and thrombosis (VITT) and shares clinical features with heparin-induced thrombocytopenia.

Due to the appearance of these cases, a group from the Department of Haematology, Oxford University Hospitals, UK, convened an expert haematology panel to evaluate patients, discuss treatment and develop consensus management guidelines. Data capture was made using an anonymised electronic reporting form submitted by a total of 182 consultant haematologist presented cases from 96 NHS trusts across the UK. The form included information on the presenting features, initial treatments, thrombosis site, any laboratory measures and associated patient outcomes. A case of VITT was defined as one where symptoms occurred within 5 to 30 days after vaccination, the presence of thrombosis, thrombocytopenia, a D-dimer level above 4000 and the presence of antibodies to platelet factor 4.

A total of 294 patients were included, of which there were 170 definite and 50 probable cases of VITT, occurring a median of 14 days after the first dose of the ChAdOx1 vaccine. The median age of patients was 48 years (55% female) and the majority (91%) of white ethnicity. Previous medical histories were available for 165 patients, of whom, 41%, had no prior medical problems and no patients had been exposed to heparin in the three months prior to their onset of VITT. The most common thrombotic site was the cerebral veins (50%). Overall mortality was 22% and the odds of death was increased 2.7-times among those cerebral thrombosis (odds ratio, OR = 2.7, 95% CI 1.4–5.2). In addition, mortality was also increased (OR = 1.7) for every 50% decrease in baseline platelet count and also by 1.7 for every increase of 10,000 in the baseline D-dimer level.

Commenting on these findings, the authors noted how the results had shown that baseline platelet count and the presence of an intracranial haemorrhage were independently associated with death. They concluded that the identification of these two potentially prognostic markers could help guide effective management of the condition.

Pavord S et el. Clinical Features of Vaccine-Induced Immune Thrombocytopenia and Thrombosis. N Engl J Med 2021

Study investigates chronic health conditions and COVID antibody response after second jab

6th August 2021

After a second vaccination, a real-world analysis showed that a quarter of those with chronic health conditions had no detectable COVID antibodies.

Vaccination against COVID-19 is critical to controlling the pandemic. Although the currently available vaccines, are very effective, it is still possible to become infected after receiving both vaccination doses. In the US, for instance, the Centers for Disease Control and Prevention, reported in May 2021, that there had been 10,262 COVID-19 vaccine breakthrough infections. These occurred in patients with a median age of 58 years and while 10% of these patients were hospitalised, fortunately only 2% died. Furthermore, in a recently published study among 1497 healthcare workers, 39 experienced a breakthrough infection and around the time of infection, neutralising antibody levels were found to be lower than in matched, uninfected control workers. Other evidence points to a reduced antibody response to vaccination among solid organ transplant recipients. With an apparent lack of data on how underlying chronic health conditions impact on antibody response, a team from the Department of Medicine, National Jewish Health, Denver, US, decided to examine the real-world antibody response among vaccine recipients with a range of underlying chronic health problems. The team used the National Jewish Health electronic medical records to identify those who were fully vaccinated and had spike IgG antibody readings done at least 14 days after the second dose. These results were considered as either positive or negative and the team used multivariate logistic regression analysis to identify any clinical characteristics associated with negative spike IgG antibody levels.

The researchers identified 226 patients with a mean age of 62 years (62% female), of whom 66% had been fully vaccinated with BNT162b and the remainder, mRNA-1273. After a mean of 62 days, just over a quarter (26%) of all patients had no detectable levels of COVID-19 antibodies, 47 given BNT162b and 11 mRNA-1273. The proportion testing negative varied considerably depending on the chronic health condition. For example, 14% of those with chronic obstructive pulmonary disease tested negative, 29% with diabetes, 46% with interstitial lung disease and the highest level, at 53%, was found in those with congestive heart failure. Using regression analysis, the authors calculated that the presence of interstitial lung disease was a significant risk factor for a negative antibody response (odds ratio, OR = 0.21, 95% CI 0.08–0.56), as was congestive heart failure (OR = 0.26) and the use of biologics or Janus kinase inhibitor drugs (OR = 0.17). Interestingly, there was no significant impact from other medicines such as systemic corticosteroids and immunosuppressants such as methotrexate, mycophenolate, azathioprine and tacrolimus.

The authors discussed that though it is widely accepted that no vaccine offers complete protection against infection, their study has raised concerns that among a proportion of patients with chronic health conditions, the absence of detectable antibodies could indicate that such individuals have no protection and are therefore at risk of breakthrough infections. Nevertheless, they also noted that to date, there have been no infections in these patients and that it is possible that an immune response could still be possible. They called for further studies of immunologic response to define ongoing COVID-19 risk in such patients.

Liao SY et al. Impaired SARS-CoV-2 mRNA vaccine antibody response in chronic medical conditions: a real-world data analysis. MedRxiv 2021

COVID Delta variant viral load similar in vaccinated and unvaccinated

5th August 2021

Similar viral loads in vaccinated and unvaccinated individuals with the COVID delta variant, suggest that both can transmit the virus.

There is now clear evidence that vaccination against COVID-19 reduces symptom burden and duration of any associated illness. An emerging problem is the appearance of new COVID-19 variants, in particular, the COVID delta variant. However, an analysis by Public Health England, has shown that two doses of a COVID-19 vaccine, reduces the incidence of hospitalisation in those infected with the delta variant. Furthermore, in the US, the Centers for Disease Control and Prevention (CDC) produced updated advice indicating how a body of evidence now suggests that full vaccinated individuals were less likely to either acquire COVID-19 or transmit the virus onto others. However, despite this, there are emerging concerns, particularly from Israel, which has managed to vaccinate a large proportion of the adult population, that the reported effectiveness of COVID-19 vaccines has reduced to 64% with regard to preventing infection and symptomatic illness. Interestingly, this reduced effectiveness appears to coincide with the spread of the COVID delta variant in the country. This is of particular concern given how it is thought that the COVID delta variant has an estimated 60% higher risk of household transmission. Thus, some uncertainty remains over the effectiveness of vaccines against the COVID delta variant and the extent to which the risk of transmission is reduced.

Potential for increased transmission
In light of this uncertainty, the CDC has released data captured from an outbreak of COVID-19 during July 2021, associated with large, public gatherings, in Massachusetts. During the month of July, 469 cases of COVID-19 associated with multiple summer events and public gatherings were reported. The reported vaccination coverage among eligible Massachusetts residents was 69% although the majority (74%) of symptomatic infected cases occurred in fully vaccinated individuals, who had received either the Pfizer-BioNTech or Jansen vaccine. Most infections (85%) occurred in males with a median age of 40 years.

A total of 133 patients provided samples for genomic analysis, of which, 89% were due to the COVID delta variant. Fortunately, only five people required hospitalisation (four who were fully vaccinated) and no deaths were reported. PCR cycle threshold (CT) values, which represent a measure of the concentration of viral load present in a sample, were taken from 127 vaccinated and 84 unvaccinated individuals. The lower the CT value, the more viral material present and the median CT values were 22.77 and 21.54 for the vaccinated and unvaccinated individuals respectively. In order words, given that the transmissibility of COVID-19 is known to be dependent on viral load, it would appear that the infection with the COVID delta variant, even among fully vaccinated individuals, could still lead to appreciable transmission of the virus. As a result of these findings, the CDC has now suggested that prevention strategies such as mask wearing should continue indoors, irrespective of vaccination status.

Source. Morbidity and Mortality weekly report. CDC 2021

Second COVID-19 vaccination safe even after initial adverse reaction

2nd August 2021

A study has found that among patients experiencing an initial adverse reaction to a COVID vaccine, the second dose is well tolerated.

The presence of an adverse reaction to a COVID-19 vaccination is uncommon, reportedly occurring in 2.5 to 11.1 cases per million doses. Reported adverse reactions have included itching, rash, hives, swelling and in some case respiratory symptoms. However, a greater potential problem is that knowledge of an immediate adverse reaction could contribute to vaccine hesitancy and thus reduced vaccination uptake. Guidance from the FDA suggested that it is safe to administer COVID-19 vaccines to individuals with a history of allergies but not to those with a history of severe allergic reactions. Furthermore, the Centers for Disease Control and Prevention, has also issued guidance on preparation for the potential management of anaphylaxis after COVID-19 vaccination, providing a pre-vaccination questionnaire and advice on the requirements for having intramuscular epinephrine readily available at vaccination centres, in case of any adverse reactions. Nevertheless, among individuals who have experienced adverse reactions to the primer or first vaccination dose, what is the likely outcome when a booster dose is administered, was a question posed by a team from the Division of Allergy, Pulmonary and Critical Care Medicine, Vanderbilt University Medical Centre, Tennessee, US. The team focused on individuals vaccinated with either the Pfizer-BioNTech or Moderna COVID-19 vaccines and who had a history of immediate and potentially allergic reactions to their prime dose. The team retrospectively examined the electronic health records to identify patients with an immediate allergic reaction which they defined as the following: symptom onset within 4 hours of the prime dose; at least one allergic symptom; referral for an allergy/immunology consultation. The presence of anaphylaxis was scored based on the Brighton and National Institute of Allergy and Infectious disease and Anaphylaxis Network criteria.

The primary outcome was second dose tolerance and which was defined as either; no immediate symptoms after the second dose or symptoms that were mild, self-limiting and or resolved with the use of an antihistamine alone.

The analysis included 189 patients with a mean age of 43 years (86% female). The first dose adverse reaction occurred in 69% given the Moderna vaccine and the most frequently reported symptoms were flushing or erythema (28%), dizziness or light-headedness (26%), tingling (24%), throat tightness (22%), hives (21%) and wheezing or shortness of breath (21%). Overall, 17% of patients met the anaphylaxis criteria. A total of 159 patients received a second vaccine dose and prophylactic antihistamines were given to 30%. All 159 patients, including 19 who had a first-dose anaphylaxis, tolerated the second dose with 20% reporting immediate and potentially allergic symptoms but which were mild and self-limited, resolving with antihistamine use.
Commenting on their results, while the authors accepted the limitation imposed by a small sample size, they reported on how the analysis indicated that it was largely safe to receive a second vaccine dose, despite the existence of an allergic reaction to the priming dose.

Krantz MS et al. Safety Evaluation of the Second Dose of Messenger RNA COVID-19 Vaccines in Patients with Immediate Reactions to the First Dose. JAMA Int Med 2021