This week I realized covid shares a characteristic with my granddaughter. Sometimes, when she is the only child in a room full of adults taking about endless banalities, she interrupts us with a "What about me?" plea. Every week I gather potential topics for this blog from key medical journal email alerts, feeds from a few selected sources like CIDRAP, scanning the Washington Post, New York Times, and Wall Street Journal dailies, watching national news broadcasts when I can, and just generally keeping my eyes and ears open. I must see dozens of potential topics to include next week, and I bookmark a subset to reconsider at the end of the week.
This week I had a few more topics than usual, around 20, that I needed to winnow down. I quickly realized that all but 1 of them were related to covid. Try as I might to include topics on general infectious diseases, covid has succeeded in becoming the center of attention this week. I'll do my best to summarize a few of the pearls.
Covid Vaccine Updates
Pediatric healthcare providers can rejoice in some more good news: according to the AAP, Moderna has joined Pfizer in allowing free returns of unused covid vaccine doses, making it less financially risky for practices to order vaccine.
A few new studies confirm high vaccine effectiveness extending into the omicron era. First, a cohort study in 4 Nordic countries looked at mRNA covid vaccine effectiveness in adolescents completing 2 vaccine doses between approximately April 2021 and April 2023. A little over 500,000 subjects were included. Vaccine effectiveness against hospitalization was 72.6% (95% CI 62.5-82.7) with a suggestion that heterologous dosing (1 Pfizer dose and 1 Moderna dose) had slightly higher effectiveness at 86.0% (56.8-100). Similar numbers were seen when just the omicron time period was analyzed at follow-up periods of 6 and 12 months. It's important to note that hospitalizations were relatively rare, regardless of vaccine status, as expected in an adolescent population. (Norway isn't included below because too few hospitalizations occurred to allow for analysis.)
Another study looked at VE in US children (5-11 yo) and adolescents (12-20 yo), the latter group in both delta and omicron periods and the former group only during the omicron period (no vaccine was available for the younger group during the delta wave). It looked at a "real world" population, i.e. not part of a formal research study but rather examining vaccine usage as implemented after authorization/approval, using data available from 7 pediatric healthcare organizations. Again VE was high, For the Pfizer vaccine during the delta time period, VE against infection was 98.4% with narrow CI (those were the good-old days at least in this one feature, no covid vaccine has great VE against infection nowadays). During the early omicron period (up through November 2022), VE against infection was 74% in the younger children and 82% in the adolescents; durability of the protection was fairly stable over a 10-month follow-up period, although the CIs became very wide because so few events occurred.
Finally I'll mention a study in the "elderly" because it contains very recent data. In Denmark, VE reported as hazard ratios of the XBB variant-based vaccine (the one in use starting last fall) was highly effective against hospitalization in this older age group. Note the very short follow-up period, this information clearly is very preliminary and could change significantly as time passes.
Covid Epidemiology
The more interesting information about covid epidemiology this week comes from abroad. First, I loved this study from the UK because it used smartphone tracing technology, preserving confidentiality, to identify important determinants of covid transmission. A key finding was that the probability of person-to-person transmission increased with time, first linearly at 1.1% per hour of exposure but extending for several days. Household exposures were most likely to result in transmission. Distance played a role of course, but longer exposures at greater distances had about equal risk of transmission as shorter exposures at shorter distances. I could spend an entire blog post and more on this article. This information can provide excellent guidance for quarantining and distancing in the event of a large covid wave in the future. Remember that the original guidance earlier in the pandemic for distancing of 6 feet was mostly a best guess to prevent transmission, no great data to guide that advice.
A report from the UK government summarizes a wealth of data as the following (see page 3 of the pdf in the link):
"... COVID-19 Omicron variant cases were most infectious around symptom onset and up to 5 days after, but could potentially be infectious for longer, especially for cases that are hospitalised, immunocompromised, or otherwise high risk. Three studies looked at transmission before symptom onset. These suggested that between a third and a half of transmission events occurred before symptom onset in the index case. However, while some studies included substantial numbers of cases, most studies included relatively few cases, and the majority of studies included cases with Omicron variant BA.1 and BA.2, with only a small number of studies reporting evidence from 2023."
This information can help inform your discussions with all those parents who wonder about transmission to high risk family members and whether to risk exposure for a special event. If you want more data than you (or I) can handle about what's going on in the UK with covid, see this link. The Excel files are massive but very interesting for those of you who want to take a deep dive.
The final mention of epidemiology is a source for concern and caution. The Pan American Health Organization, PAHO, that is the branch of the WHO overseeing public health in the Americas, reported on respiratory illness activity in the southern hemisphere which is now in summer season. The key take-home point here is that, although North American is driving a lot of the SARS-CoV-2 positivity now, there is significant covid illness in Central and South America. This implies that covid is not quite a winter respiratory virus, at least not yet.
Covid Bottom Lines
As we enter our 4th year of covid, I realized I've learned a few key lessons to be applied for the future:
- It's difficult to compare illness rates and other outcomes in the US over the years, primarily because we aren't collecting information in the same way as we did early in the pandemic. Wastewater data are mostly obtained as they were before, but this is at best a qualitative data source.
- Covid vaccines are the most closely studied and monitored in history with now over 5 billion people worldwide receiving at least one dose. Every credible study/report has confirmed that, regardless of age or underlying risk factors, vaccinated individuals will have better outcomes than being unaccinated and infected, even after being infected multiple times. This takes into account all adverse events following vaccination itself. For virtually every individual, vaccination is the better choice. From a public health perspective, vaccination of some low risk groups may not be cost effective. This is why the UK, for example, does not provide vaccine for some healthy children; UK health authorities have decided the money is better spent on other aspects of health care.
- Although there are similarities, SARS-CoV-2 is not just like influenza virus. The mutation rate is much higher, meaning that we still face a faster moving target for new vaccine and therapeutic drug development. Also, as mentioned above, seasonality isn't yet clear. So far SARS-CoV-2 isn't just a winter respiratory virus.
- Even though the omicron era seems to have brought less disease severity, SARS-CoV-2 is still a major killer, now at a rate of about 1500 deaths per week.
Please encourage everyone to be up-to-date on covid and all other vaccines.
WRIS
Winter Respiratory Infection Season clearly is still with us. I await more data to see if the winter school break resulted in fewer, greater, or had no effect on WRIS infection numbers. However, I did notice a report from China that provided evidence that school breaks lessened influenza transmission during the years 2015-2018.
RSV-NET: CDC is still projecting a downturn nationally, but too early to be certain of this.
FluView still shows significant influenza-like illness activity, at least as of a week ago. It's definitely not too late to be vaccinated.
And ... More What About Me
It's my blog, what could be a more pitiful plea for attention? So, speaking of me, note that the CDC published the 2024 adult immunization guide that not only includes old codgers such as yours truly but also extends down to 19 years of age.
One last bit, an update to my bird feeder adventures I mentioned last week. I had a great few days of multiple bird species sightings, followed by a squirrel invasion - those dastardly rodents cleaned out the birdseed supply in a couple days. I've now been researching squirrel deterrents, being careful to not actually hurt them although I admit to having occasional sciuricidal thoughts. It looks like I'll be moving the feeder and engaging in some high-wire techniques to squirrel-proof the new location, hoping I don't end up with a spectacular ladder fall and resultant visit to my local ER.