Does your risk of long COVID differ by variant?


A: Two recent studies point to yes.

TL:DR; Among vaccinated people, the odds of reporting long COVID were lower for the Omicron BA.1 variant compared to Delta, but higher for Omicron BA.2 compared to BA.1.

Study #1

In the UK, researchers identified ~56K people newly diagnosed with COVID-19 during the Omicron BA.1 wave and ~41K people diagnosed during the Delta wave.

People were included in the study if they tested positive (PCR or antigen) for COVID after vaccination and self-reported their symptoms via an app at least once per week for 28 days after they were diagnosed with COVID. People who reported new or ongoing symptoms ≳ 4 weeks after their initial diagnosis were classified as having long COVID.

The study found that 4.5% of cases from the Omicron wave met the criteria for long COVID compared to 10.8% from the Delta wave. A similar pattern was observed regardless of how long it had been since people were vaccinated.

A major strength of this study was that they statistically accounted for any differences in age, sex, area-level deprivation, comorbidities, number of vaccine doses, and body-mass index across those diagnosed during each surge. In other words, the results shouldn’t be purely due to different types of people getting infected during the Omicron versus Delta waves.

An important limitation is that people who choose to use a symptom reporting app may be different from those who do not, thus the results may not generalize to the entire UK population. In addition, the definition of long COVID in this study was ANY new or ongoing symptom ≳ 4 weeks after their initial diagnosis, which doesn’t tell us much about the specific symptoms or severity of symptoms people experienced. Finally, the researchers did not directly test for specific variants in individuals, but used the timing of infection as an indicator of variant.

Study # 2:

Using the UK population-based ONS Coronavirus Infection Study, researchers in the UK identified 10K people diagnosed with COVID-19 during the Delta surge or with confirmed Delta infection after Omicron began to circulate. They compared this group to ~24K+ people with confirmed Omicron BA.1 infection and ~8K people with confirmed infection with the Omicron BA.2 variant.

People were included in the analysis if they tested positive for COVID (PCR) after vaccination and self-reported whether they were still experiencing symptoms > 4 weeks after they first had COVID-19 via a survey of people aimed to be representative of the UK population. If they answered ‘yes’, they were classified as having long COVID. People were also asked whether their symptoms limited their ability to carry-out daily activities.

The study found that ~8.5% of cases from the Omicron BA.1 wave met the criteria for long COVID compared to ~16% from the Delta wave, among people who were double vaccinated. In addition, ~9.5% of cases from the Omicron BA.2 wave met the criteria for long COVID, whereas <8% of cases from the BA.1 wave did, among those triple vaccinated. No differences in the proportion with long COVID were found when comparing Delta cases to Omicron BA.1 cases or BA.2 cases, among those triple vaccinated. (A very high percentage of the UK population was triple vaccinated by January 2022). Results were similar when they focused on symptoms that limited people’s daily activities.

Like the first study, researchers statistically accounted for differences in age, sex, area-level deprivation, pre-existing health or disability status and vaccination status (double or triple vaxxed) or time since last COVID-19 vaccine (BA.1 vs. BA.2 comparison). Researchers also used genotyping to verify the variant people were infected with for periods in which multiple variants were circulating. While similar to the first study, the criteria for long COVID used was self-reported symptoms > 4 weeks after initial diagnosis, they also considered the impact of symptoms on daily activities. This study also has the important advantage of being based on nationally representative data and thus results are generalizable to the UK population.

Both of these studies estimated long COVID rates among vaccinated people only, likely because with high vaccine uptake there were small numbers of unvaccinated people in the UK studies. While still emerging, there is good evidence that vaccination itself lowers the risk of long COVID (See here for more info.)

Overall, it is good news that the odds of long COVID among people infected during the Omicron surge was lower than during the Delta surge! But given the much higher number of infections during Omicron, this still means a lot of people who might be facing long-term complications. We are also still learning how other variants (BA.4 and BA.5) match up against BA.1, BA.2, and Delta in terms of long COVID risk and what the risks of long COVID are in children vs. adults. Given these unknowns, it is still worth avoiding infection (and re-infection) when you can.

To read about the first study, visit here.

To read about the second study, visit here.

For more on study considerations, see here or here.

Link to Original FB Post