A study of healthcare and other frontline workers with COVID-19 showed that a history of two or three messenger ribonucleic acid (mRNA) vaccine doses lessened the severity of illness significantly. In a study that included the original Wuhan strain and the Delta and Omicron variants, workers who had two or three doses of vaccine had less fever and chills, less need for medical care, and the viral load in the bloodstream was much lower than in the non-vaccinated cohort.
This analysis was conducted among 1,199 participants with SARS-CoV-2 from Dec. 14, 2020, to April 19, 2022, with follow-up until May 9, 2022, reported.
“Workers in Arizona, Florida, Minnesota, Oregon, Texas, and Utah [had] COVID-19 infection confirmed by reverse transcriptase-polymerase chain reaction testing and lineage classified by whole genome sequencing of specimens,” the authors reported.1
Overall, 14.0% were infected with the origin strain, 24.0% with the Delta variant, and 62.0% with the Omicron variant.
“Participants with Delta and Omicron infections who received the second dose 14 to 149 days before infection had a significantly lower mean viral load compared with unvaccinated participants,” the authors note. “[Overall], recent vaccination with two or three mRNA vaccine doses less than 50 days before infection with Delta or Omicron variants — compared with being unvaccinated — was associated with attenuated symptoms, duration of illness, [and less] medical care seeking.”
Hospital Infection Control and Prevention sought additional comment on the study by co-author by Lauren Olsho, PhD, principal associate for health & environment with the multinational firm Abt Associates.
HIC: How many healthcare workers were included in the study, and were their findings different from the general population?
Olsho: Our [overall] study follows a cohort of over 5,000 essential frontline workers whose jobs require face-to-face interaction with the public. About half are healthcare workers. Of those, about a third are primary health providers — physicians, physician assistants, and nurse practitioners. The other two-thirds are allied healthcare personnel, including nurses, therapists, technicians, and others providing clinical support.
Healthcare worker participants are more likely to be vaccinated or boosted against COVID-19. They also have had fewer COVID-19 infections. Only about 20% of our healthcare workers tested positive for COVID-19 since the Pfizer and Moderna vaccines first became available. That compares with 25% of first responders and other essential frontline workers. Some of this difference is probably due to the higher vaccination rates, but we also see higher reported rates of masking while at work among healthcare workers. It’s likely that also explains some of the difference in infection rates.
Overall, our healthcare workers are a dedicated and conscientious group. This study has been going since July 2020, and some of our healthcare worker participants have been with us since the beginning. Despite being physically, mentally, and emotionally stretched, they complete survey questions, send us swabs for testing every single week like clockwork, and even provide blood samples. We are so grateful to our participants for all they’ve put into the study.
HIC: You demonstrate less severe infection in those who took two and particularly three doses of the mRNA vaccines. Based on these findings, would you recommend the new mRNA booster with an Omicron component for essential workers and healthcare workers?
Olsho: Our findings show milder symptoms for those who were recently vaccinated and especially those who recently received a third dose. Based on these findings, I’d absolutely recommend the new Omicron booster for healthcare workers and other essential workers, especially for those who haven’t received a recent dose.
The new booster might work even better since it’s aligned to the variant that’s still in active circulation. For once, we’re not playing catch-up. That said, things change fast with this virus. We’re already hearing of new variants and subvariants popping up worldwide, so people shouldn’t delay getting the new booster if they want to maximize the benefit.
HIC: Why do you think the third dose in particular was protective, elevated antibody titers or perhaps a “deeper” response from T and B immune system cells?
Olsho: This article did not incorporate data on immune response, but other studies have shown that repeated exposure, whether through vaccine doses or COVID-19 infection, improves immune memory. Our study shows that, even among mild breakthrough infections, this improved immunity reduces overall symptoms and lowers the chance of having a fever or needing medical attention.
HIC: Did you find symptoms of some two-shot cases were akin to those unvaccinated? If that’s right, could it be attributed to waning immunity?
Olsho: During the Omicron wave in particular, we found that symptoms among those with two doses were statistically indistinguishable from those who were unvaccinated. It’s possible that waning immunity contributed to this finding, although you’d need a much larger sample to tell for sure. We’ve been digging into this a bit more since the article was published, and it turns out there’s also something else going on that’s an increasing challenge in this type of research.
For symptoms, in particular, we rely on what our participants tell us they’re feeling. But vaccinated and especially boosted participants were more likely than the unvaccinated to report having any symptoms when they have them, whether infected or not.
The end result is that while vaccinated people have fewer symptoms, they report them more often when they do occur, while unvaccinated people have more symptoms but report them less frequently. So you end up with the data suggesting the two groups are more similar than they actually are.
HIC: Do any of your findings have implications for long COVID — is it still more likely to occur in the unvaccinated?
Olsho: Our results showed shorter duration of symptoms for those who were recently vaccinated or boosted, but we didn’t look at long COVID. That said, we do definitely have participants in our sample who report symptoms for many weeks after infection. We’ve just recently launched an effort to follow up with participants about symptoms of long COVID, so I hope we’ll be in a position to say more on this soon.
- The HEROES-RECOVER Network; Thompson MG, Yoon SK, Naleway AL, et al. Association of mRNA vaccination with clinical and virologic features of COVID-19 among US Eesential and frontline workers. JAMA 2022;328:1523-1533.
