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Can Two Doses of COVID-19 Vaccines Be from Different Brands? The Lancet Publishes Preliminary Safety Data from "Mix-and-Match" Trial

Posting Date：2021-05-14Views：
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To address challenges such as limited vaccine supply, the strategy of "mix-and-match" vaccination with different vaccines has gained international attention. However, data on the immunogenicity, reactogenicity, or safety of such regimens have been lacking.
 

Today, The Lancet published important data from a large randomized trial in the UK. By evaluating combination regimens of the AstraZeneca COVID-19 vaccine ChAdOx1 nCoV-19 and the Pfizer/BioNTech COVID-19 vaccine BNT162b2, the study provides preliminary safety data on mix-and-match vaccination, analyzing local and systemic reactions in participants, as well as laboratory blood and biochemical test results.

 

 

The Com-COV study, led by a team from the University of Oxford, is a multicenter, participant-blinded, randomized heterologous prime-boost COVID-19 vaccination study in the UK. It aims to provide evidence to guide different vaccine combination strategies, in order to offer greater flexibility in vaccination schedules and facilitate timely vaccination for more people.

 
The study employed a two-dose vaccination regimen (prime and boost), comparing four combination strategies using the two vaccines BNT162b2 (referred to as BNT) and ChAdOx1 nCoV-19 (referred to as ChAd), as well as the effects of different dosing intervals (28 days or 84 days). The four vaccination combinations were: two doses of ChAd, two doses of BNT, ChAd followed by BNT, and BNT followed by ChAd; both dosing intervals were tested for all four combinations.
 
The study enrolled 830 participants, all aged 50 years or older, with no comorbidities or only mild to moderate well-controlled comorbidities. This analysis provides preliminary reactogenicity and safety data: reactogenicity data were obtained from participants in the 28-day interval group through self-reported local and systemic symptoms collected within 7 days after each dose; hematologic and biochemical safety monitoring data were collected from 100 participants in the 28-day interval group at baseline (before the first dose), on day 28 (before the second dose), and 7 days after the second dose.
 

A total of 463 participants had a two-dose interval of 28 days; all received the first dose, and 461 received the second booster dose. The median age of the 463 participants was 57 years (range 50-69), 46% were female, 25% were from ethnic minority groups, and baseline characteristics were balanced across the four different "mix-and-match" groups.

 

 

Results showed that among those receiving two doses of the same vaccine, systemic reactogenicity was higher after the first dose in the ChAd group and after the second dose in the BNT group.
 
Compared with two doses of the same vaccine, both mix-and-match regimens resulted in more pronounced systemic reactions after the second dose.
 
Taking self-reported feverishness as an example:

  • Among recipients of the ChAd/BNT combination, 34% (37 of 110) reported this reaction, compared with 10% (11 of 112) among recipients of two doses of ChAd, an absolute difference of 24% (95% CI 13%-35%).

  • Among recipients of the BNT/ChAd combination, 41% (47 of 114) reported this reaction, compared with 21% (24 of 112) among recipients of two doses of BNT, an absolute difference of 21% (95% CI 8%-33%).

 

Similar trends were observed for chills, fatigue, headache, joint pain, malaise, and muscle soreness. No participants were hospitalized due to these symptoms. Most reactions occurred within 48 hours after vaccination.

 

 

▲Self-reported local and systemic reactions, and their severity, within 7 days after the first dose (prime, top three rows) and within 7 days after the second dose (boost, bottom three rows). (Image source: Reference [1]; click to enlarge)
Local reactions include: hardening, itching, pain, redness, swelling, and warmth at the injection site.Systemic reactions include: chills, fatigue, fever (≥38.0°C), feverishness (without temperature recorded), headache, joint pain, malaise, muscle soreness, nausea, vomiting, and diarrhea.
Severity levels: mild, moderate, severe, and hospitalization.

 
 
Before the study began, participants were informed that acetaminophen might reduce vaccine side effects, but researchers did not actively advise prophylactic use. Actual results showed that a certain proportion of participants in each group took acetaminophen within 48 hours after the second dose, with a higher proportion in the mix-and-match groups.

  • Two doses of ChAd: 36% (40 of 112),

  • ChAd/BNT combination: 57% (63 of 110),

  • Two doses of BNT: 41% (48 of 117),

  • BNT/ChAd combination: 60% (68 of 114).

 
The paper noted, "It is particularly noteworthy that these data were obtained in participants aged over 50 years, and reactogenicity may be higher in younger populations."
 

Hematologic and biochemical profiles were similar between participants receiving two doses of the same vaccine and those receiving mix-and-match regimens. All laboratory adverse events in the mix-and-match groups were grade 2 or lower; no thrombocytopenia was observed in any group on day 7 after the booster dose.

 

The paper concluded, "Pending fuller safety data and immunogenicity results, these data suggest that the heterologous regimens used in the Com-COV study may have some short-term effects, and acetaminophen may help alleviate these symptoms. Reassuringly, all reactogenicity symptoms were transient, and the limited hematologic and biochemical data raised no concerns."
 

Dr. Matthew Snape, Professor of Vaccinology at the University of Oxford and corresponding author of the study, added, "Importantly, there are no safety issues or signals, but this does not tell us whether the immune response will be affected. We hope to report these data in the coming months."

 

The Com-COV study is ongoing, evaluating the long-term effects of heterologous BNT162b2 and ChAdOx1 nCoV-19 vaccination regimens. Primary immunological outcome data are expected in June 2021, and the study will also include additional analyses on whether prophylactic or routine use of acetaminophen reduces these reactions. Furthermore, the research team will evaluate combination regimens of other available COVID-19 vaccines. Longer-term data are expected to provide further insights into mix-and-match vaccination.

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