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Mix and match strategy for booster dose is safe and effective

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Dr Surya Kant, Professor and Head, Dept. of Respiratory Medicine, KGMU, UP, Lucknow. National Vice Chairman IMA-AMS    19 October 2021

Interim analysis of data from an ongoing study in the US published as a preprint suggests that homologous and heterologous Covid vaccine booster dose enhance immune response in persons who had completed their primary vaccination with any one of the three currently approved Covid -19 vaccines.1

In this multisite study, 458 healthy adults, mean age 50-55 years, fully vaccinated with either Pfizer, Moderna or J&J Covid vaccine at least 12 weeks earlier and had no reported history of SARS-CoV-2 infection were administered a booster injection with either the same vaccine as the one already taken or a different vaccine, creating nine possible combinations). 154 received mRNA-1273, 150 received Ad26.CoV2.S, and 154 received BNT162b2 booster vaccines. Blood samples were collected at baseline (before taking the booster vaccine), day 15 and day 29.

It was found that persons who had taken the J&J vaccine had 3- to 15-fold lower baseline serum binding antibody levels compared to those who had taken the Pfizer or Moderna vaccines. An increase in binding antibody levels was seen in all the participant groups. A 2-fold or greater rise was seen in 98-100% of J&J vaccine recipients, 96-100% of Moderna vaccine recipients and 98-100% of Pfizer vaccine recipients following booster dose with Moderna vaccine. The geometric mean fold rises in binding antibody levels at Day 15 were greatest for those who received the Pfizer and Moderna vaccine booster after J&J primary vaccination (33- and 56-fold respectively). The J&J booster dose increased binding antibody titers in all except those who had taken J&J as the primary vaccine, where the antibody levels were 7-10-fold lower than those who had received an mRNA vaccine earlier.

All participants had detectable binding antibody levels to the delta variant after the booster dose, and the level was only 15-36% lower compared with the Wa-1 strain.

Serum neutralizing antibody levels prior to booster vaccination were approximately 3-and 10-fold lower for Pfizer and J&J recipients, respectively, compared to recipients of the Moderna vaccine. The geometric mean fold rises in neutralization titers were greatest for J&J vaccine recipients, followed by Pfizer and Moderna recipients. Persons who received an mRNA-based booster vaccination had a four-fold increase in their neutralization response more frequently than those who were boosted with J&J.

Homologous booster dose increased neutralizing antibody titers 4.2- to 20-fold whereas heterologous booster dose resulted in 6.2-to 76-fold increase in antibody titers.

Sixteen percent of recipients of Moderna booster dose, 12% of J&J and 14% of Pfizer booster dose recipients reported vaccine-related adverse events, which usually occurred 1-3 days after the booster dose and were mostly mild in nature such as headache, injection site pain, malaise and myalgia. Acute renal failure and acute cholecystitis were reported in two patients, but both were considered unrelated to the vaccine.

Covid vaccine booster dose is a hot topic of discussion nowadays and perhaps rightly so. India started its vaccination drive on 16th January. It has been almost 10 months since health care workers and front-line workers took the vaccine. Since then, many new variants of concern have emerged, particularly the delta variant, which proved to be a deadly strain. Several studies have shown declining immunity after the primary vaccination, which is a cause for concern and validates the need for a booster shot.

Making the case for a booster dose, this study has shown that all booster doses, whether homologous and heterologous, were immunogenic regardless of the primary vaccine taken. The mix and match strategy elicited higher immunogenic response and therefore offered greater protection.

Reference

Atmar RL, et al. Heterologous SARS-CoV-2 booster vaccinations: Preliminary report. medRxiv October 13, 2021; doi: https://doi.org/10.1101/2021.10.10.21264827

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