Public health impact of SARS-CoV-2 Omicron subvariant BA.5 compared to BA.2 in Denmark

In a recent study published in of lancet infectionresearchers conducted a nationwide study in Denmark to assess the public health impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) omicron subvariant BA.5 compared to BA.2. did.

Background

Denmark has one of the highest rates of messenger ribonucleic acid (mRNA) vaccination. In Denmark, about 9% of people over the age of 18 are not vaccinated. Additionally, reverse transcription polymerase chain reaction (RT-PCR) testing is free in Denmark.

Nevertheless, Denmark experienced a massive Omicron wave from December 2021 to February 2022. During this 3-month period, approximately 35% of the adult population tested positive for her RT-PCR. After January 2022, he dominated BA.2 until BA.5 came along.

About research

In this study, researchers first identified all Danish adults who ordered an RT-PCR test between 10 April and 30 June 2022. The country’s coronavirus disease 2019 (COVID-19) surveillance system has confirmed that these people have her COVID-19 as the primary diagnosis. They used a case-control design to identify people infected with BA.5 or BA.2 during the study period.

First, the team calculated the immune protection against breakthrough infection with BA.5 or BA.2 and hospitalization in individuals vaccinated three times by RT-PCR-confirmed Omicron infection (Analysis 1). .

They then compared relative vaccination status to estimate vaccine-induced immunity to both variants (analysis 2). Finally, they determined and compared her COVID-19 hospitalizations of her BA.5 and BA.2 infected people (Analysis 3). The reference group for the sensitivity analysis consisted of people who had completed the first vaccination series more than 4.5 months before her on 30 June 2022.

Finally, researchers used logistic regression models to estimate immune protection from previous infections with 95% confidence intervals (CI). They presented it as 1 minus the model-derived odds ratio (OR), similar to how they estimate vaccine efficacy. They adjusted this model for sex, age, region, comorbidities, and time of RT-PCR sampling. The last is a categorical variable.

Survey results

Of the 414,436 RT-PCR tested during the study period, analyzes 1, 2, and 3 consisted of 187,347, 42,150, and 48,119, respectively. Prior Omicron infections provided adequate protection against subsequent BA.5 breakthrough infections. On the other hand, previous Alpha or Delta infections provided relatively weak protection against both BA.5 and BA.2.

This analysis did not assess the impact of reduced immunity as a function of time from vaccination or previous infection. Therefore, the investigators concluded that the weak immune protection observed in patients with a previous Alpha/Delta infection compared to Omicron infection was not due to decreased efficacy, but decreased cross-reactive immunity to different VOCs. I didn’t think it was due to

Prior SARS-CoV-2 infection provided higher protection against BA.2 than BA.5 during the study period. Results remained the same in sensitivity analyzes employing a matched case-control design. Vaccine-induced immunity was similar for both BA.2 and BA.5. BA.5 showed slightly more immune escape in recipients who received two vaccinations. However, more data may help arrive at a more accurate estimate. Furthermore, the results of this study show a higher hospitalization rate for BA.5 cases compared to BA.2 cases (almost 3-fold).

However, there is little evidence of the severity of BA.5 infections. While Portugal reported weeks of excess mortality, a pre-print study from South Africa found that the risk of severe hospitalization and mortality was significantly higher during the BA.4–BA.5 wave compared with the previous BA.1 wave. The significantly higher protective estimates in the current study reflect a hybrid immune effect in the Danish vaccinated population. Even after accounting for bias, the degree of immune protection remained high at about 85% among previously infected people.

Conclusion

The current study found that prior Omicron infection in individuals vaccinated three times conferred significant protection against BA.5 breakthrough infection and subsequent hospitalization. Vaccine protection against BA.5 breakthrough infection was slightly weaker.

Authorities have identified the first Omicron BA.5 case in Denmark on 10 April 2022. Since then, Denmark has subjected more than 83% of all positive cases to whole-genome sequencing (WGS). In nearly 85% of these cases, genomic data were obtained to help researchers identify the responsible VOCs. Indeed, this study highlights that WGS remains a mainstay of SARS-CoV-2 surveillance in Denmark.

Overall, the current BA.5 wave had little adverse effect on the Danish population due to advanced hybrid immunity. Importantly, this effect was nearly identical to that with previous Omicron BA.1/BA.2 driving waves. However, BA.5 led to more hospitalizations than his Omicron BA.2, so future studies should investigate the severity of his BA.5 disease.