ChAdOx1 n-COV 19 Vaccine Protected Health Care Workers From Severe Infection Caused by the Variants

To the Editor:

India has recently witnessed the “tsunami” of the second coronavirus disease 2019 wave, which resulted in more than 400,000 new cases at its peak in mid-May 2021.¹ The infections occurring after 2 weeks of the complete vaccination are termed breakthrough infections (BTIs).² These BTIs occur in a small percentage of vaccinated persons.³

We report the incidence and clinical implications of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants in our symptomatic health care workers (HCWs) with postvaccination infections (PVIs). Between January 16 and April 24, 2021, 3235 HCWs were immunized with ChAdOx1 n-COV 19 vaccine-recombinant. Eighty-five (2.6%) of them acquired PVIs. The majority were young adults, with an average age of 34.2 years. Among these, 51 were fully vaccinated with 2 doses (73.91%). The time for the onset of symptoms after vaccination ranged from 2 to 86 days, with an average of 34.8 days.

We analyzed the available real-time polymerase chain reaction (RT-PCR) samples of 69 of these positive HCWs with genome sequencing. The predominant infections occurred from the B.1.617.2 lineage (49.25%), followed by B.1 (28.35%), and B.1.1.7 (11.94%) strains (Table ). A total of 61.19% were the variants of concern (VOC; eg, the Delta and Alfa variants).

Table.

Distribution of Lineage of SARS-COV-2 Mutants in the Fully and Partially Vaccinated Groups (N=69)

SARS-CoV-2 lineage	Fully vaccinated group (n=51)	Partially vaccinated group (n=18)	Total n (%)
B.1	15	4	19 (27.5)
B.1.1	3	1	4 (5.97)
B.1.1.7 (Alpha variant of concern)	6	2	8 (11.94)
B.1.393	1	1	2 (2.98)
B.1.596	1	0	1 (1.49)
B.1.617.2 (Delta variant of concern)	23	10	33 (49.25)
No content (excluded)	2	0	2 (2.89)

A significant difference (P<.05) was observed between the early infections (<2 weeks) compared with late infections (>2 weeks) in all age groups. There were two hospital admissions (2.89%) but no intensive care unit (ICU) admissions and deaths. Both the admitted cases were adult males aged 46 and 64 years, respectively. They acquired the infection after 21 and 24 days, respectively, of their last vaccination and were infected with the Alpha and Delta variants, respectively.

SARS-COV-2 infections after coronavirus disease 2019 vaccination have been recognized globally and are a cause of concern. These infections may occur after partial or complete vaccination for several reasons, such as inadequate development of immunity, lack of safety precautions, and the emergence of VOC.⁴ The VOC are highly transmissible and can bypass the immunity of any individual, even after full vaccination.³ There is available evidence that the vaccination may make illness after BTI less severe.² The majority of our cohort also had minor infections, none required admission in the ICU, and there were no deaths. These findings are significant because more than half of the cohort was infected with the VOC and still escaped the severe illness. We acknowledge that our cohort had a younger population and did not have major medical comorbidities. Hence, these results cannot be translated to the older population who may be at a higher risk of acquiring severe infection. However, we noted a high incidence of hospital and ICU admissions and deaths among cases who were not vaccinated in a separate study.⁵

A small subset of HCWs demonstrated PVIs with SARS-COV-2. The most common cause of these infections were the mutant virus B.1.617.2, B.1, and B.1.1.7 strains. Although these were lineages of VOC, prior vaccination protected this younger cohort from any severe disease requiring hospital and ICU admissions and deaths.