Situation of COVID-19 after six years and a contemporary reassessment of vaccine efficacy
- Jaspreet Singh
- Aug 7
- 4 min read
Updated: 2 days ago
Contents:
Abstracts
Introduction
Vaccine technologies and global rollout
mRNA Vaccines
Viral vector vaccines
Conclusion
Abstract:
It has been six years since the COVID-19 virus first emerged from a small region in China and rapidly escalated into a global pandemic. Although the world is no longer gripped by the same level of crisis as in 2020, new variants of the virus continue to emerge, posing recurring threats to public health. These variants—while often less severe—still manage to affect large segments of the population, underscoring the virus's ability to evolve and persist.
In light of recent strains such as Nimbus and Stratus gaining traction globally, this article begins by briefly examining the current variant landscape in 2025. It then offers a comprehensive review of all COVID-19 vaccines developed over the past six years, spanning mRNA, viral vector, inactivated, protein subunit, and DNA platforms.
Introduction:
The COVID-19 pandemic, which began in late 2019, reshaped global public health, economies, and scientific collaboration at an unprecedented scale. Although the initial waves were marked by severe illness, hospitalizations, and strict lockdowns, the current state in 2025 is relatively stable. However, the virus continues to evolve, giving rise to new variants like Nimbus and Stratus, which have demonstrated higher transmissibility and partial immune escape. These developments raise ongoing questions about long-term protection and the role of vaccines that are being developed and used so far.
Current variants overview:
Nimbus (NB.1.8.1, first appeared Jan 2025, now the dominant strain in the U.S., representing ~43% of cases per CDC. Symptoms remain typical (fever, cough, fatigue), but patients note a particularly painful “razor blade” sore throat.
Stratus (XFG / XFG.3), officially named XFG, informally “Stratus” (also dubbed “Frankenstein” due to its recombinant origin), contains nine extra spike protein mutations associated with partial immune escape. Noted symptoms include hoarseness, sore throat, dry cough and fever.
In India (e.g., Madhya Pradesh), XFG dominates recent cases (>60%), with Nimbus nearly absent.
Vaccine technologies and global rollout:
Since the onset of the COVID-19 pandemic, the development of vaccines has marked a turning point in the global response to SARS-CoV-2. Governments, pharmaceutical companies, and research institutions worldwide accelerated vaccine development using multiple platforms, each with unique mechanisms, delivery systems, and storage requirements. This section explores the major categories of COVID-19 vaccines and their worldwide distribution over the past six years.
mRNA vaccines:
mRNA vaccines represent a breakthrough in modern vaccinology. These vaccines deliver synthetic messenger RNA encoding the spike protein of SARS-CoV-2, which, once translated in human cells, induces an immune response. Pfizer–BioNTech, the first COVID-19 vaccine to receive Emergency Use Authorization (EUA) in December 2020. Widely administered globally with billions of doses delivered.
Viral Vector Vaccines:
These vaccines use a harmless adenovirus to deliver genetic material coding for the SARS-CoV-2 spike protein. Johnson & Johnson, Sputnik V and Oxford–AstraZeneca are a few examples.
Due to the rapid global response to the pandemic, a wide array of vaccine platforms was developed and deployed. These included inactivated virus vaccines such as Sinovac and Covaxin, protein subunit vaccines like Novavax, and even DNA-based options such as ZyCoV-D. Each of these contributed uniquely to the pandemic response, with varying degrees of efficacy, accessibility, and public acceptance. While a detailed examination of every individual vaccine is beyond the scope of this article, the diversity of platforms developed globally underscores the scale and urgency of scientific innovation prompted by COVID-19.
India’s COVID-19 vaccination journey has been marked by a diverse portfolio of vaccine platforms. Covishield, developed by Oxford–AstraZeneca and manufactured by the Serum Institute of India, was the first to be widely rolled out in January 2021. It demonstrated an efficacy of around 70% in standard dosing regimens and remained effective in preventing severe disease even during the Delta wave. Alongside it, Covaxin, India’s indigenous inactivated virus vaccine developed by Bharat Biotech in collaboration with ICMR, showed approximately 78% efficacy against symptomatic COVID-19 and over 90% efficacy in preventing severe outcomes. Additionally, ZyCoV-D, the world’s first DNA plasmid vaccine developed by Zydus Cadila, was approved in August 2021 with an efficacy of around 66.6%. Though innovative, its three-dose, needle-free delivery system limited its widespread adoption.
These vaccines formed the foundation of India’s pandemic response. Yet, as the virus continues to evolve, the long-term effectiveness of these efforts remains a subject of global scrutiny and scientific investigation.
Conclusion:
Even six years after its emergence, COVID-19 continues to evolve through new variants like Nimbus and Stratus, highlighting the virus’s persistent threat. The global rollout of diverse vaccine platforms has significantly reduced severe illness and mortality, especially in countries like India. However, waning immunity and variant-driven challenges emphasize the need for updated vaccines, continued surveillance, and strong public health measures. The pandemic may be under control, but its impact is far from over—and vigilance remains essential.
References:
World Health Organisation (WHO):
Tracking SARS-CoV-2 variants
Centers for Disease Control and Prevention (CDC):
COVID-19 Vaccine Effectiveness – Updates and Data.
https://www.cdc.gov/coronavirus/2019-ncov/vaccines/effectiveness/work.html
BBC Health:
COVID vaccine effectiveness: What we know so far.
Johns Hopkins University:
Understanding Vaccine Effectiveness and Breakthrough Infections.
Indian Council of Medical Research (ICMR):
ICMR Bulletin on Vaccine Effectiveness and COVID Studies
Very informative 👏🏻
How deeply COVID has penetrated into our lives for so long now
A fine piece of explanation..great work.
Very informative and well written