Is NB.1.8.1 already in India? Inside the ICMR’s variant surveillance in May 2025

New Delhi, May 28, 2025 (Updated): As the NB.1.8.1 subvariant of SARS-CoV-2 spreads globally across over 22 countries, including China, Singapore, and the United States, Indian health authorities are ramping up surveillance efforts. The Indian Council of Medical Research (ICMR) and INSACOG have stated that, as of now, NB.1.8.1 has not been detected in Indian samples. However, genomic surveillance at key airports and across clinical labs has been intensified in response to the variant’s role in Hong Kong’s most severe COVID-19 wave in over a year. Samples collected from passengers arriving at Mumbai, Delhi, Kochi, and Chennai airports are being prioritized for sequencing. State governments in Tamil Nadu and Maharashtra have also been instructed to increase monitoring following regional alerts.

Why Is NB.1.8.1 Being Closely Watched?

NB.1.8.1 was added to the World Health Organization’s Variant Under Monitoring (VUM) list on May 23, 2025, after being linked to a sharp increase in severe COVID-19 cases and hospitalizations in Hong Kong. It is a descendent of the JN.1 Omicron lineage and shares several key spike protein mutations—A435S, V445H, T478I, and Q493E—with the LP.8.1 subvariant, which is currently dominant in the United States. Early laboratory studies reviewed by WHO’s Technical Advisory Group on Virus Evolution have suggested that NB.1.8.1 displays a 1.5 to 1.6-fold reduction in neutralization from prior vaccination or infection, indicating some degree of immune escape. Despite this, WHO maintains that there is no current evidence of increased severity. Indian authorities are treating the global rise of NB.1.8.1 as an early-warning signal and are acting preemptively given past lapses in variant detection during the Delta and Omicron waves.

How Is India’s COVID Surveillance System Operating in 2025?

INSACOG now coordinates over 100 labs across the country and continues to function as India’s primary genome sequencing network. Its current mandate includes routine surveillance of positive RT-PCR samples, cluster-based outbreak tracking, and wastewater sequencing in major cities such as Ahmedabad, Pune, Bengaluru, and Hyderabad. Following global alerts on NB.1.8.1, INSACOG has activated its variant-triggered surveillance protocol, with emphasis on sequencing from symptomatic international travelers, ICU patients, and immunocompromised individuals. While sequencing capacity has improved since 2021, virologists warn that rural areas and tier-2 towns may still experience delays in sample submission or genome turnaround, which could allow early variant spread to go unnoticed.

What Symptoms Are Associated With NB.1.8.1?

Reports from Hong Kong and Singapore indicate that NB.1.8.1 infections mirror those of earlier Omicron subvariants. Patients often present with sore throat, dry cough, fatigue, mild fever, and nasal congestion. Some elderly patients have also experienced gastrointestinal symptoms such as nausea and diarrhea. Indian hospitals have been issued advisory notes by ICMR recommending vigilance in respiratory wards, especially for geriatric patients with pre-existing conditions. The Ministry of Health and Family Welfare has requested that all tertiary hospitals log and report symptom anomalies during COVID admissions over the next two weeks. Clinical escalation such as rapid oxygen desaturation, seen in Hong Kong’s elderly population, is a particular concern in India due to booster gaps in vulnerable groups.

Are India’s Vaccines Effective Against This Variant?

India’s vaccine portfolio currently includes Covishield, Covaxin, Corbevax, and the mRNA-based Gemcovac, though none are formulated specifically against NB.1.8.1 or LP.8.1. Immunologists at the Translational Health Science and Technology Institute have indicated that while neutralizing antibody levels may be reduced against NB.1.8.1, cellular immunity from prior vaccination likely remains robust enough to prevent severe outcomes in most people. Preliminary modeling suggests that breakthrough infections may rise in the absence of updated boosters. Both Serum Institute of India and Bharat Biotech are reported to be working on updated monovalent formulations in line with WHO’s recommendations, though no rollout timelines have been publicly announced. As of now, no Indian vaccine manufacturer has applied for emergency use authorization for an LP.8.1-specific booster.

What Is the Status of India’s Booster Coverage?

Booster coverage across India remains patchy. National data as of May 2025 shows that only 24 percent of eligible adults have received a second booster. Uptake in urban centers such as Delhi and Mumbai is relatively high, nearing 40 percent, while states like Uttar Pradesh, Madhya Pradesh, and Bihar remain below 20 percent. Among individuals over 60, the booster coverage stands at 31 percent, far below what is needed for herd-level protection. According to MoHFW data, interest in COVID vaccination has dropped steadily since 2024, particularly as younger populations perceive the threat of severe disease to be low. NTAGI is scheduled to meet in June to review global efficacy data on LP.8.1-targeted boosters and determine whether India should proceed with a limited or national-level booster push in the second half of the year.

What Preventive Measures Are Underway?

In anticipation of potential variant introduction, MoHFW has instructed airport health officers to restart RT-PCR testing for symptomatic international arrivals from NB.1.8.1 hotspots, including Hong Kong, Singapore, and parts of the U.S. Surveillance teams have been placed on alert at major railway stations and interstate bus terminals in urban districts. Meanwhile, local governments in Maharashtra, Kerala, and Tamil Nadu have been asked to reinstate genome-linked wastewater surveillance and maintain oxygen buffer stock in district hospitals. National Civil Aviation authorities have not reinstated travel restrictions but have advised enhanced sanitation protocols at airports and mask recommendations in enclosed zones.

Could India Face a Surge Similar to Hong Kong?

While India’s demographic profile is younger and prior infection rates are higher, the risk of regional outbreaks remains if NB.1.8.1 achieves community transmission. Experts caution that the monsoon season, coupled with weakened adherence to masking and poor booster uptake in senior citizens, could amplify transmission if the variant arrives undetected. Dr. Nivedita Gupta, a senior scientist with ICMR, has stated that India is not facing an immediate COVID emergency, but sustained vigilance is essential. Geriatric wards and long-term care facilities in metropolitan areas have been placed under heightened surveillance. District medical officers have been asked to submit contingency plans for ICU triage and oxygen delivery systems within the next two weeks.

What Comes Next?

INSACOG is expected to release its next monthly variant report in early June. MoHFW is working in coordination with NTAGI and the Department of Biotechnology to assess readiness for a fall booster strategy. While no NB.1.8.1-linked hospitalization clusters have been identified so far, health officials acknowledge that early detection is critical to avoid the mistakes of past surges. WHO will also re-evaluate the global risk level of NB.1.8.1 by mid-June. For India, the weeks ahead will be a crucial test of whether investments in surveillance, vaccination, and public health preparedness can prevent another wave from gaining momentum.