When several European countries paused use of the Oxford/AstraZeneca Covid vaccine in March 2021, the criticism from many commentators was swift, extreme…
Adapting for Variants: Early Results or Trials Underway for 38 Versions of 17 Covid Vaccines
Seventeen vaccines with at least one variant-adapted version sounds like a lot. But none are actually in use yet. And given all the hype about how quickly and easily adapted vaccines could be delivered, it’s remarkable how little data we’ve seen well over a year since the first variant of concern emerged. We had gotten used to a high level of transparency about the development of the Covid vaccines leading the pack in the US and Europe. That’s not the rule any more.
For example, I haven’t been able to find any preclinical reports for the various BNT/Pfizer adapted versions in clinical trials, including for the Alpha variant. Another example: even when there are late stage clinical trials, protocols aren’t to be found, either.
Before we get to the studies and results we can see, let’s zoom out to the big picture. Several vaccination strategies are being studied for expanding or strengthening our immune systems against Covid variants:
- Boosting with an additional dose of the same vaccine;
- Boosting with a dose of a different vaccine (heterologous vaccination);
- Adapting a vaccine for a variant;
- Multivalent vaccines – combinations of original plus adapted version(s), or combinations of adapted versions;
- Vaccine so wide-ranging, it’s hoped to be more or less variant-proof – or even effective for all coronaviruses.
I posted a roundup of evidence and ongoing trials for the first 2 of those strategies in late January. In general, they both increase protection against variants, with heterologous boosting often making a particularly large difference for vaccines with somewhat lower initial effectiveness. (That post included a table listing laboratory studies of responses to Delta and/or Omicron after boosters: an updated version of that is below this post.)
This post is looking at the next 2 strategies: adapted and multivalent vaccines.
My key takeaways? We seem to be on the brink of seeing meaningful clinical trial results for some adapted vaccines. And from the research results that have been released so far, it seems likely that at least some of these vaccines will provide better protection against the variants circulating now – and, critically, perhaps broaden immunity enough for greater protection from the next ones.
Just as the original vaccines based on the virus’ early strains reduced the risk of severe outcomes from variants that were very different, adapted vaccines based on variants that are no longer a threat could do that, too. For example, as we’ll see later in this post, a “press teaser” finding from a randomized trial suggests the Alpha-adapted BNT/Pfizer vaccine could possibly be substantially more protective against Omicron than the original formulation. (Proviso here: the companies released far too little information about this to be sure about how good it was.) And Sanofi’s Beta-adapted protein subunit vaccine may even have increased the potential for protection against original SARS in a preclinical study. On the other hand, some don’t work as well as another shot of the original.
This next stage of vaccine development is very complex, as researchers grapple with a shape-shifting virus, and the complexity of so many possible vaccine adaptations, too. Multivalent vaccine development escalates that complexity: that’s a mixture of vaccines in one dose, which adds questions to the list about multiple possible vaccine combinations and how much of each to add to the mix.
All this comes as an overlay to the complicated issues of boosting with different vaccines if/when we have adapted vaccines tested only in people who had that same vaccine. Today, 63% of the world’s people have had at least a dose of a vaccine – and it’s a real patchwork of vaccines, often changed up along the way to 2 or 3 shots. And as if all that isn’t complex enough, there’s the question of intranasal administration: one of the vaccines in this post suggests that could make a meaningful difference for at least some adapted vaccine boosters.
There’s lots more to cover, though, so let’s dig in. Here’s how I’ve broken this post down:
- Overview of vaccines, variants, and studies
- Digging into the results
- Full list of studies on variant-adapted Covid vaccines and combinations
- Addendum: Updated list of laboratory studies including immune responses to Delta and/or Omicron after boosters
Overview of vaccines, variants, and studies
I found 39 studies reported or underway for 38 adapted vaccines or combinations, from 17 vaccine groups – 7 of which have original formulations of vaccines in use in at least one country. Most are mRNA or protein subunit vaccines. There are sure to be other adapted versions that don’t have published results or clinical trials registered, or for vaccines that are earlier in the pipeline, so expect a stream to keep coming. (I monitor vaccines when they release preclinical or clinical results, as well as any that have announced a phase 3 trial.)
The vaccines in this collection include adaptations for 4 of the 5 variants of concern – none are for Gamma. There are vaccines adapted to 1 or 2 of them, and one vaccine adapted to all 4. The variants of concern so far have points in common as well as differences with the original virus that vaccines were formulated to recognize. Here’s a diagram showing how much the 5 variants of concern vary genetically (by Stuart Ray of John Hopkins):
Another variant of concern could be close to what we’ve already encountered – or it could strike out in a newer direction, as Omicron did. The studies on the impact of adapted vaccines will help us learn what can strengthen immune systems to face SARS-CoV-2 variants. The studies tallied in this post include:
- Results of 19 preclinical studies.
- 20 clinical trials underway, mostly phase 2, for around 16,500 participants globally, plus unstated number for Sanofi vaccine (possibly 10,000).
- Results for subsets of clinical trial participants for adaptations of 1 vaccine (Moderna), and some fragments of data from another (BNT/Pfizer).
Most of the vaccines are ones that aren’t yet rolled out in their original formulation – and for one of them, the first formulation is already adapted for variants (Alpha and Beta, with a later version covering Alpha, Beta, Delta, and Omicron).
The 17 vaccines that have adapted versions include:
- 7 mRNA vaccines and 1 self-amplifying RNA, 5 protein subunit vaccines, 2 adenoviral vector vaccines, 1 inactivated vaccine, and 1 DNA vaccine. (One of the mRNA vaccines is lyophilized (freeze-dried) and one of the protein subunit vaccines has an intranasal version of adapted vaccine.)
- 7 that are already in use in original formulation (AstraZeneca, BNT/Pfizer, CovIran (Shifa Pharmed), J&J, Medigen, Moderna, Novavax) – 4 of those with adapted versions in clinical trials (AZ, BNT/Pfizer, Medigen, and Moderna).
- 12 that are multivalent, and another that’s called a hybrid – it’s not a mix of 2 vaxes, but it’s targeted to 2 variants. They’re nearly all bivalent – including 2 versions of the vaccine – but one is quadrivalent: for protection against 4 strains of the virus (Alpha, Beta, Delta, and Omicron).
Digging into the results
Overall, there is a lot of uncertainty around these findings. They are almost all very small, preclinical studies. Some carry more weight than others, though, because they’re better-designed and conducted, with better reporting of what was done.
Animal results aren’t going to be a precise substitute for what happens in people, but there’s a spectrum here, too. Data in non-human primates is likely to be closer to what could be expected in humans, for example. Confirmation of results in experiments in more than one type or species of animal strengthens confidence in the reliability of conclusions, as well. And there can be differences between the techniques used in the studies – such as whether researchers analyzed immune responses in enough ways, and used tests based on actual viruses, or pseudovirus tests only.
There are 2 broad types of preclinical studies here:
- Studies of potential immunity only – analyzing immune responses in the animals, to identify whether they might be able to provide protection against particular variants;
- Challenge experiments, where the researchers try to infect the animals with virus after vaccination, and then analyze immune responses as well as other outcomes like weight loss (which suggests severe disease), and infection and viral loads.
Although I looked at a range of aspects of the studies to consider how to weigh them, in my opinion, whether or not the researchers included challenge experiments and/or randomized non-human primates turned out to be markers for dividing this set of studies into a “stronger” and a “weaker” group.
I’ve also looked at what the researchers conclude about antibody/antigenic imprinting (“original antigenic sin”). That’s when the immune system is so firmly influenced by a first encounter to a vaccine or antigen, its responses are heavily shaped by that original memory. (Derek Lowe discusses this phenomenon here). If that happens with a Covid vaccine, then a variant-adapted booster mightn’t have much impact. But I don’t have the technical expertise to discuss the design choices of the various adaptations made to the vaccines, and their possible implications.
First up, I’ve got a table showing the variant-specific vaccines that have public results, tagging those that have challenge experiments. After that, I discuss some issues I think are noteworthy, followed by a brief overview of results, vaccine by vaccine. That’s broken down into a pair of tables – for those with stronger and weaker evidence – so that the ones I think have greater uncertainty are clearly separated.
There are links to get you to the studies in 2 places: the overviews include links to the records for the vaccines in my collection – split into the ones for adapted vaccines, and all records. That’s a lot to navigate for the vaccines with many studies, though. So there are links to each individual study, whether or not they have results, in the full list of studies.
Vaccines with results for adapted versions for variants
* Includes challenge experiment(s)
|Variant||Preclinical (non-human animals)||Clinical (human)|
|Alpha||HDT Bio (saRNA)*||BNT/Pfizer|
|Beta||ACM Biolabs (protein subunit – intranasal)*|
AstraZeneca (AZ) (adenoviral)
Clover (protein subunit)
HDT Bio (saRNA)*
Novavax (protein subunit)*
Sanofi (protein subunit)
|Delta||Academia Sinica Taiwan (mRNA)|
Shenzhen Rhegen (mRNA – lyophilized)*
|Omicron||Academia Sinica Taiwan (mRNA)|
Chinese Academy of Military Sciences/Walvax (mRNA)
Chinese Academy of Sciences (mRNA)
CovIran (Shifa Pharmed) (inactivated)
HDT Bio (saRNA)
Shanghai Key Laboratory Fudan (DNA)
Shenzhen Rhegen (mRNA – lyophilized)*
There’s a lot of variety in these experiments – for example, whether or not they were testing the vaccine as a booster or a primary series (the first vaccination cycle, which is usually 2 shots). And there’s a lot of variety in the results, too. Most of the researchers conclude the vaccines could be an improvement on original formulations, but we won’t know if the differences are meaningful until we see how they work in people.
The question of “antigenic sin” has gotten a fair bit of attention in discussions on social media, as some researchers have suggested it might be a factor in the results of the vaccine they studied. However, most don’t. Some of the “weaker” group of studies either didn’t test the vaccine as a booster, or had no comparison group, so the question is very open for them.
There are only reports from studies in humans for 2 vaccines, BNT/Pfizer and Moderna.
For the first, BNT/Pfizer’s, it’s results from a randomized trial – but it was just a single slide in a press briefing, with nowhere near enough information to know how certain we can be about the results presented. It was for the ability to neutralize Omicron after vaccination with an Alpha-adapted variant, one for Delta, or a bivalent one of both. That they had this data suggests that BNT/Pfizer will be first past the post in the late stage clinical trial results race again.
The second, Moderna’s, has plenty of data, but it’s actually more complicated. While I think researchers for this vaccine had the strongest methodology of any of the preclinical studies (by Ying and colleagues, 2021), the clinical research reports are problematic. They are 2 exploratory studies, where they’ve taken small subsets of participants from more than a single study each time, without the selection process being fully described, and with other factors driving up the risk of bias.
For now, then, we’re really left with the preclinical studies. So finally, some points I think are noteworthy from those:
- When an adapted vaccine didn’t seem to do better than the original vaccine, that tended to be because of apparently weaker potential to protect against other versions of the virus it wasn’t targeted at – the adapted vaccines typically worked well against the variant they were aiming for.
- Multivalent vaccines didn’t always do better, but they mostly worked at least as well as the most protective vaccine in the mix, and sometimes better.
- The number of variants tested for ability to respond in these studies was often quite small: many were done before the recent variants had emerged, for example. Still, many of the vaccines seemed to have a very broad range of potential protection. I already mentioned an example of one that was widely tested: Sanofi’s protein subunit vaccine may even have increased protection for the original SARS, which is a different coronavirus. (It improved outcomes for all the SARS-CoV-2 variants tested, too – original, Alpha, Beta, Gamma, and Delta.)
- One of the mRNA vaccines was lyophilized (freeze-dried) – from Shenzhen Rhegen Biotech and other collaborators in China.
- As I mentioned early in this post, there was an intranasal version of an adapted vaccine in this set of studies, and that may have enhanced its potential effectiveness. It’s for the protein subunit vaccine from ACM Biolabs (a company based in Singapore and Switzerland). (There are quite a lot of studies on intranasal or other mucosal delivery of a variety of Covid vaccines, but I haven’t added a tag for that yet in my collection – though I’m sure that’s just around the corner!)
Overview of results for stronger studies*
* Includes challenge experiment and/or randomized non-human primates, and additional stronger preclinical research methods, such as live virus assays, multiple animal types, and/or randomization of other animals.
** Includes include clinical research.
|Signs of improvement over original?||Records|
|Possibly yes (as a booster)|
(Only tested against Omicron)
|HDT Bio (saRNA)|
Alpha, Beta, Omicron
|Possibly yes (alone as a primary series)|
Possibly not as a booster*
(*Only Omicron version tested as booster)
|ACM Biolabs (protein subunit)|
|Possibly yes for intranasal version (alone as a primary series)|
Multivalent, possibly not*
(*Not tested in an intranasal version)
|Possibly yes (as a booster)||Adapted|
Beta, Original+Beta, Delta, Beta+Delta, Omicron
|Mixed results – roughly similar to original||Adapted|
|Novavax (protein subunit)|
|Possibly yes (alone or as booster)||Adapted|
|Sanofi (protein subunit)|
|Possibly yes, adjuvanted or multivalent (as booster to the original vax or Sanofi’s mRNA vax)||Adapted|
|Shenzhen Rhegen (mRNA, lyophilized)|
|Possibly yes for Delta adaptation (alone as a primary series)|
(Possibly not for Omicron adaptation – weaker evidence)
Overview of results of weaker studies
|Signs of improvement over original?||Records|
|Possibly not (as primary series or booster)||Adapted|
|Clover (protein subunit)|
|Possibly yes (as primary series or booster)||Adapted|
|Academia Sinica Taiwan (mRNA)|
Delta, Delta+Omicron, Hybrid with characteristics of Delta and Omicron
|Possibly yes (as primary series for Delta and Delta+Omicron versions)|
Possibly not for Omicron or hybrid versions
|Chinese Academy of Military Sciences/Walvax (mRNA)|
|No data for comparison to original||Adapted|
|Chinese Academy of Sciences (mRNA)|
|Possibly not (as primary series – not tested as booster)||Adapted|
|Shanghai Key Laboratory Fudan (DNA)|
|Possibly yes (as a booster)||Adapted|
|Shifa Pharmed (inactivated)|
|No data for comparison to original||Adapted|
Full list of studies on variant-adapted Covid vaccines and combinations
Listed alphabetically by vaccine technical name; booster status detailed when previous vaccine is from a different developer
* Original vaccine rolled out in at least 1 country in February 2022
|Vaccine, type, manufacturer||Variant(s) adaptation||Participants||Location(s)||Research phase|
|Beta||24 non-human primates (macaques).||USA.||Preclinical. Results.|
Chinese Academy of Military Sciences/Walvax
|Omicron||At least 17 mice (2 types) (number unclear).||China.||Preclinical. Results.|
|Omicron||45 mice, 2 guinea pigs.||Iran.||Preclinical. Results.|
|Alpha; Delta; multivalent (Alpha & Delta)||1,245 people.||South Africa, Turkey, USA.||Phase 2. (Subset report in a press briefing.)|
|Beta||137 people.||Germany.||Phase 2.|
|Omicron||1,420 people (according to press release).||Not specified – could be Brazil, Canada, South Africa, USA.||Substudy D in phase 3 trial.|
|Beta; multivalent (original + Beta)||Mice, number unclear (5-7 per group, ca 7 groups).||UK.||Preclinical. Results.|
|Beta||2,848 people.||Brazil, Poland, South Africa, UK.||Phase 2/3.|
|CoV2 preS dTM|
|Beta; multivalent (original + Beta)||40 non-human primates (macaques).||USA.||Preclinical. Results.|
|Multivalent (original + Beta)||Not stated (whole trial is 722 people).||Australia, France, Honduras, Kenya, Spain, UK, USA.||Phase 2/3 trial.|
|Multivalent (original + Beta)||Possibly 10,000 people.||Colombia, Ghana, Honduras, India, Japan, Kenya, Mexico, Nepal, Sri Lanka, USA.||Phase 3 trial.|
|Alpha; Beta||20 mice and 24 hamsters.||USA.||Preclinical. Results.|
|Omicron||15 mice and 18 hamsters.||USA.||Preclinical. Results.|
|Beta; multivalent (original + Beta)||30 mice (number unclear).||USA.||Preclinical. Results.|
|Beta; multivalent (original + Beta)||Mice (2 types), number unclear (6-9 mice per group, 4 groups in 2 experiments).||USA.||Preclinical. Results.|
|Beta||32 non-human primates (macaques).||USA.||Preclinical. Results.|
|Beta||135 people.||USA.||Phase 1.|
|Beta; multivalent (original + Beta)||660 people.||USA.||Phase 2. Results (for subset of 80, 60 from one study and 20 from another).|
|Multivalent (original + Beta); Delta; multivalent (Beta + Delta)||3,620 people.||USA.||Phase 2/3 trial. Results (for 120 people, including a subset of 100 from 5 of the 8 trial arms, plus 20 unboosted people from the main phase 3 trial).|
|Omicron||16 mice (3 types) (number unclear).||USA.||Preclinical. Results.|
|Omicron||16 non-human primates (macaques).||USA.||Preclinical. Results.|
|Omicron||2,924 people (aged 16 or older).||UK.||Phase 2/3 trial.|
|Omicron (and multivalent – unspecified)||300 people.||USA.||Phase 2 trial. (Press release – extension of other registered trials, but not clear which.)|
Chinese Academy of Sciences
|Omicron||21 mice.||China.||Preclinical. Results.|
|Beta||160 people.||Taiwan.||Phase 2 trial.|
|Beta, multivalent (original + Beta)||>80 mice; >9 non-human primates (baboons) (numbers unclear).||USA.||Preclinical. Results.|
|Beta, multivalent (original + Beta)||Mice, number unclear (16-32 per group in first stage with 4 groups).||China.||Preclinical. Results.|
|Beta||152 people.||Australia.||Phase 1 trial.|
Shenzhou Cell Engineering (Sinocelltech)
|Multivalent (Alpha + Beta)||752 people.||China.||Phase 1/2 trial. (Additional info source)|
|Multivalent (Alpha + Beta)||300 people.||United Arab Emirates.||Phase 1/2 trial (as booster after 2 doses of mRNA vaccine).|
|Multivalent (Alpha + Beta)||300 people.||United Arab Emirates.||Phase 1/2 trial (as booster after 2 doses of inactivated vaccine).|
|Multivalent (Alpha + Beta)||240 people (aged 12 and over).||Not stated.||Phase 2 trial (single dose of multivalent vaccine or BNT/Pfizer after 2-dose Sinopharm Beijing vaccine)|
|Multivalent (Alpha + Beta)||600 people.||Not stated.||Phase 2 trial (single dose of multivalent, BNT/Pfizer, or Sinopharm vaccine after previous 2-doses of Sinopharm, Moderna, or BNT-Pfizer vaccines or Covid infection)|
|Multivalent (Alpha + Beta), multivalent (Alpha + Beta + Delta + Omicron)||300 people (aged 12 and over).||Not stated.||Phase 2 trial (one of each, or 2 of the 4-variant version, or single dose Sinopharm Beijing vaccine plus 4-variant version).|
|Multivalent (Alpha + Beta + Delta + Omicron)||360 people.||Not stated.||Phase 2 trial (2 doses multivalent, or dose each of BNT/Pfizer and multivalent, or 2 doses BNT/Pfizer – after 2 doses of Moderna or BNT-Pfizer)|
Academia Sinica Taiwan
|Delta, Omicron, hybrid (characteristics of Delta + Omicron), multivalent (Delta + Omicron)||Mice, number unclear.||Taiwan.||Preclinical. Results.|
Protein subunit (intranasal)
|Beta, multivalent (original + Beta)||5 mice, 48 hamsters.||Singapore, USA.||Preclinical. Results.|
Shanghai Key Laboratory Fudan
|Omicron||22 mice.||China.||Preclinical. Results.|
Shenzhen Rhegen Biotech + others
|Delta, Omicron||36 mice (2 types).||China.||Preclinical. Results.|
All my Absolutely Maybe Covid-19 vaccine posts
All previous Covid-19 posts at Absolutely Maybe
My posts at The Atlantic, at WIRED, and debunking posts at my personal website.
Notes on my collection of studies are here. The collection is in a public Zotero library you can dig into here.
Disclosures: My interest in Covid-19 vaccine trials is as a person worried about the virus, as my son is immunocompromised: I have no financial or professional interest in the vaccines. I have worked for an institute of the NIH in the past, but not the one working on vaccines (NIAID). More about me.
The cartoons are my own (CC BY-NC-ND license). (More cartoons at Statistically Funny.)
The representation of similarity between Covid variants of concern comes from Wikimedia Commons, based on data from NextStrain on December 1, 2021 by Stuart Ray from Johns Hopkins (wiki name, Soupvector).
Update [February 24, 2022]: Added Sanofi phase 3 trial to studies underway.
Updated list of laboratory studies including responses to Delta and/or Omicron after boosters
This is an update of a list included in a post from late January, including a summary of the studies up to January 25.
|Vaccine(s)||Type of study||Variants of Concern||Results|
|3rd dose of Sinovac’s CoronaVac||Humans, blood tests||Beta, Gamma, Delta||Wang (Sept 5)|
|3rd dose of Moderna’s vax, either adapted for Beta or original or multivalent (combination of original and adapted in one dose)||Humans, blood tests||Beta, Gamma, Delta||Choi (Sept 15)|
|3rd dose of Sanofi’s protein subunit vax (original & version adapted for Beta), after doses of that vax or their mRNA vax||Preclinical, non-human primates||Alpha, Beta, Gamma, Delta||Pavot (Sept 21)|
|2nd or 3rd dose of Medigen’s protein subunit vax adapted for Beta, after dose(s) of original, and 3 doses of original||Preclinical, non-primates||Alpha, Beta, Gamma, Delta||Kuo (Oct 15)|
|3rd dose of Sinovac’s CoronaVac||Humans, blood tests||Alpha, Beta, Delta||Yue (Oct 19)|
|3rd dose of Moderna, either adapted for Beta or original||Preclinical, non-human primates||Beta, Delta, Epsilon, Gamma, Iota||Corbett (Oct 21)|
|3rd dose of Sinopharm’s Beijing vax||Humans, blood tests||Beta, Delta, Lambda||Ju (Nov 10)|
|3rd dose of Pfizer||Humans, blood tests||Delta, Omicron||Basile (Dec 13)|
|2 or 3 doses of Pfizer, 1 dose of J&J, or 1 or 2 doses of Moderna||Humans, blood tests||Omicron||Schmidt (Dec 13)|
|2-dose course of Moderna followed by half-dosage Moderna||Humans, blood tests||Beta, Omicron||Doria-Rose (Dec 20)|
|3rd dose of Moderna in half and full dosages, original, adapted for Beta or Omicron, or multivalent||Humans, blood tests||Omicron||Moderna press release (Dec 20)|
|2-dose course of Sputnik V (Sputnik Light [rAd26-S] followed by second Sputnik V vaccine [rAd5-S]), followed by another dose of Sputnik Light||Humans, blood tests||Omicron||Dolzhikova (Dec 21)|
|3rd dose of Moderna or Pfizer in people with multiple sclerosis on anti-CD20 treatment||Humans, blood tests||Delta, Omicron||Madelon (Dec 21)|
|2 doses of Novavax followed by a 3rd dose||Humans, blood tests||Delta, Omicron||Novavax press release (Dec 22)|
|2-dose courses of Moderna or Pfizer or single-shot J&J; additional mRNA vax (as 3rd after mRNA or 2nd after J&J), either homologous or heterologous||Humans, blood tests||Delta, Omicron||Garcia-Beltran (December 23)|
|3 doses of Pfizer||Humans, blood tests||Delta, Omicron||Hoffmann (Dec 23)|
|3rd dose of Pfizer||Humans, blood tests||Delta, Omicron||Ariën (Dec 24)|
|2 or 3 doses of Pfizer||Humans, blood tests||Delta, Omicron||Lusvarghi (Dec 28)|
|2-dose course of AZ, Moderna or Pfizer or single-shot J&J; dose of Pfizer after 2-dose Moderna or single-shot J&J||Humans, blood tests||Beta, Delta, Omicron||GeurtsvanKessel (Dec 29) (Feb 4)|
|2-dose course of CoronaVac followed by a dose of Pfizer||Humans, blood tests||Delta, Omicron||Perez-Then (Dec 29)|
|2-dose course of AZ, Moderna or Pfizer; 3rd dose of Pfizer after AZ, Pfizer or Moderna 2-course; 3rd dose of Moderna after AZ 2-course; Moderna or Pfizer dose after single-shot J&J||Humans, blood tests||Omicron||De Marco (Dec 30)|
|2-dose course of Pfizer followed by 3rd dose of J&J or Pfizer||Humans, blood tests||Omicron||Tan (Dec 30)|
|2-dose courses of Pfizer or Moderna or 3rd dose of Moderna or Pfizer||Humans, blood tests||Beta, Omicron||Carreño (Dec 31)|
|2-dose course of Moderna or Pfizer or single-shot J&J; booster dose of Moderna or Pfizer||Humans, blood tests||Delta, Omicron||Saharia (Jan 1)|
|3-dose course of AZ or Pfizer||Humans, blood tests||Alpha, Beta, Gamma, Delta, Omicron||Dejnirattisai (Jan 3)|
|2-dose course of AZ, Moderna, or Pfizer; 2-dose course of AZ or Pfizer with 3rd dose of Moderna or Pfizer||Humans, blood tests||Alpha, Delta, Omicron||Willett (Jan 3)|
|2-dose courses of AZ, Moderna and/or Pfizer with 12-week interval; 2-dose course of Pfizer with short interval with 3rd dose of Moderna or Pfizer||Humans, blood tests||Delta, Omicron||Belik (Jan 5)|
|2-dose courses of CoronaVac or Sinopharm Beijing with 3rd dose of either Moderna or Pfizer||Humans, blood tests||Beta, Delta, Omicron||Zuo (Jan 6)|
|2-dose courses of AZ or Pfizer with third dose of Pfizer||Humans, blood tests||Delta, Omicron||Faustini (Jan 8)|
|1 to 3 doses of Moderna or Pfizer||Humans, blood tests||Beta, Delta, Omicron||Banerjee (Jan 13)|
|2 doses of J&J; 2 doses of Moderna with 3rd half- or full-dose Moderna; 3 doses of Pfizer; 2 doses of Pfizer with 3rd dose of J&J; 1 dose of J&J with Pfizer 2nd dose||Humans, blood tests||Omicron||Lyke (Jan 14)|
|2-dose course of Sinopharm Beijing; 3-dose course of Sinopharm Beijing or 3rd dose of ZF2001||Humans, blood tests||Omicron||Wang (Jan 15)|
|2-dose course of Moderna or Pfizer with 3rd dose of Moderna or Pfizer||Humans, blood tests||Omicron||Jergovic (Jan 16)|
|3-dose course of Pfizer||Humans, blood tests||Beta, Delta, Omicron||Muik (Jan 18) (by BioNTech/Pfizer)|
|2-dose course of CoronaVac or AZ, or 3-dose course of AZ||Human, blood tests||Alpha, Beta, Delta, Omicron||Suntronwong (Jan 18)|
|3-dose courses of Moderna or Pfizer||Human, blood tests||Beta, Delta, Omicron||Walls (Jan 19)|
|3-dose course of Pfizer||Human, blood tests||Omicron||Wu (Jan 19)|
|2- and 3-dose courses of Pfizer||Human, blood tests||Omicron||Xia (Jan 22)|
|2-dose courses of AZ or Pfizer, 3rd dose Pfizer (people with cancer)||Human, blood tests||Omicron||Fendler (Jan 25)|
|2-dose course of Pfizer, 3rd dose Pfizer (longitudinal study)||Human, blood tests||Alpha, Beta, Gamma, Delta, Omicron||Wratil (Jan 28)|
|2-dose course of Moderna or Pfizer, 3rd dose of same (longitudinal study of healthcare workers)||Human, blood tests||Beta, Delta, Omicron||Debes (Jan 31)|
|2-dose course of Moderna, 3rd dose of Moderna or Moderna adapted for Omicron||Preclinical, non-human primates||Omicron||Gagne (Feb 4)|
|2-dose course of Pfizer or 1-dose J&J, 3rd dose of Pfizer or J&J||Preclinical, non-human primates||Delta, Omicron||Chandrashekar (Feb 7)|
|2-dose course of Moderna or Pfizer, 3rd dose of Moderna or Pfizer||Human, blood tests||Omicron (BA1, BA2)||Iketani (Feb 9)|
|2-dose course of Moderna, 3rd dose of Moderna or Moderna adapted for Omicron||Preclinical, mice||Omicron||Ying (Feb 9)|
|2-dose course of Moderna or Pfizer, 3rd dose of same vaccine (people who had breakthrough infections)||Human, blood tests||Delta, Omicron||Gaebler (Feb 11)|