The booster dose of mRNA Covid-19 vaccines are effective in reducing the chances of hospitalization due to reinfection in persons with previous Covid-19, according to a recent study from the Centers for Disease Control and Prevention (CDC) published in the latest issue of CDC’s Morbidity and Mortality Weekly Report.¹

In this study, researchers reviewed electronic health records of 51,609 patients who had been hospitalized with Covid-19-like illness more than 3 months after they had recovered from a previous infection and underwent Nucleic Acid Amplification Test, (NAAT) for SARS-CoV-2 infection; of these, 5048 had a positive NAAT result. This study was undertaken to look into the effectiveness of Covid-19 mRNA vaccines (Pfizer-BioNTech and Moderna) and the booster doses against hospitalization due to reinfection. Among the 5000 NAAT positive patients, 2436 (48.3%) were admitted during the Delta wave and 2612 (51.7%) during the Omicron surge. Sixty-one percent of the patients had not been vaccinated; 4.3% had taken one vaccine dose, 27.6% had received two doses and nearly 7% had received a booster dose. The corresponding figures among the control group were 47.5%, 5.5%, 33.2% and ~14%, respectively.

The effectiveness of two doses of vaccine against hospitalization due to Covid-19 reinfection was 47.5% during the delta wave, from June to mid-December 2021. This increased to nearly 58% after the booster dose. During the Omicron-driven wave, from mid-December through February, the vaccine effectiveness after two doses was 34.6%, but the effectiveness of the booster against hospitalization due to Omicron was almost 68%.

Results of this study show that the mRNA vaccines reduced reinfection hospitalizations among persons with previous infection. This protective effect against severe disease was augmented by the booster dose. Hence, all eligible persons, including those who have had Covid-19 earlier, must complete their vaccination, including booster dose on schedule. Apart from vaccination, other Covid-appropriate behaviors like masking, physical distancing, hand washing, avoiding crowded public places and poorly ventilated closed spaces must be strictly adhered to, in order to mitigate their risk, particularly now when there is an uptick in the number of Covid cases in the country.

Reference

1. Plumb ID, et al. Effectiveness of COVID-19 mRNA vaccination in preventing COVID-19-associated hospitalization among adults with previous SARS-CoV-2 infection - United States, June 2021-February 2022. MMWR Morb Mortal Wkly Rep. 2022 Apr 15;71(15):549-555. doi: 10.15585/mmwr.mm7115e2.