These are different protocols claimed to have some degree of effectiveness at either/both reducing risk of infection with Covid-19 or reducing severity of Covid-19, if you become infected. These different protocols are not meant to be combined; however, there is quite a bit of overlap between some of them.
In no particular order:
1. MATH+ Protocol
This is primarily a treatment protocol for patients in hospital. It was developed by Dr. Paul Marik, famous for his past treatment protocol for sepsis (called HAT or the Marik protocol). He adapted that protocol for Covid-19, calling it MATH+.
One part of the protocol is for prophylaxis (prevention). Here is the September 2nd update to that Protocol:
While there is extremely limited data, the following “cocktail” may have a role in the
prevention/mitigation of COVID-19 disease. This cocktail is inexpensive, safe, and widely available. It
should be noted that a recent publication suggests that melatonin my reduce the risk of COVID-19
infection,  while many papers suggest that Vitamin D deficiency increases the risk of infection and is
associated with a significantly worse outcome. [2-12]
* Melatonin (slow release): Begin with 0.3mg and increase as tolerated to 2 mg at night [1,13-17]
* Vitamin D3 2000-4000 u/day [2-12]
* Vitamin C 500 mg BID (twice daily) and Quercetin 250-500 mg BID [10,11,18-26]
* Zinc 50-75 mg/day (elemental zinc). Zinc lozenges are preferred. After 1 month, reduce the
dose to 30-50 mg/day. [10,11,18,25,27-31]
* Optional: Famotidine 20-40 mg/day [32-35]
* Optional/Experimental: Interferon-? nasal spray for health care workers 
* Optional: Ivermectin for post-exposure prophylaxis (see ClinTrials.gov NCT04422561)”
The reference numbers above are found in the PDF file linked here.
Protocol for Low and Moderate Risk Patients:
* Elemental Zinc 25 mg once a day
* Vitamin C 1000 mg once a day
* Quercetin 500 mg (OTC) once a day
~ If Quercetin is unavailable, then use Epigallocatechin-gallate (EGCG) 400 mg (OTC) once a day [EGCG is found in Green Tea extract]
Protocol for High Risk Patients:
* Elemental Zinc 25mg once a day
* Hydroxychloroquine (HCQ) 200 mg once a day for 5 days, then once a week.
~ If HCQ is unavailable then use Low and Moderate risk protocol [see above]
3. Vitamin D
Some researchers are simply recommending high levels of vitamin D as a prophylaxis. The list of 21+ studies here show that vitamin D has the effect of reducing risk of infection, of a severe case, and of death from Covid-19.
In addition, Grant et al. recommend 10,000 IU per day for a few weeks, and then continuing at a dose of 5,000 IU/day. They also state that for person who become ill with Covid-19, higher doses might be useful.
Grant, William B., et al. “Evidence that vitamin D supplementation could reduce risk of influenza and COVID-19 infections and deaths.” Nutrients 12.4 (2020): 988.
– “To reduce the risk of infection, it is recommended that people at risk of influenza and/or COVID-19 consider taking 10,000 IU/d of vitamin D3 for a few weeks to rapidly raise 25(OH)D concentrations, followed by 5000 IU/d…. For treatment of people who become infected with COVID-19, higher vitamin D3 doses might be useful.”
In a study prior to Covid-19, Garland et al. note that about 10,000 IU per day is the level needed to raise vitamin D levels to the optimum range, and that even doses as high as 40,000 IU per day are safe:
Garland, Cedric F., et al. “Vitamin D supplement doses and serum 25-hydroxyvitamin D in the range associated with cancer prevention.” Anticancer research 31.2 (2011): 607-611.
– “Results: Serum 25(OH)D rose as a function of self-reported vitamin D supplement ingestion in a curvilinear fashion, with no intakes of 10,000 IU/d or lower producing 25(OH)D values above the lower-bound of the zone of potential toxicity (200 ng/ml). Unsupplemented all-source input was estimated at 3,300 IU/d. The supplemental dose ensuring that 97.5% of this population achieved a serum 25(OH)D of at least 40 ng/ml was 9,600 IU/d. Conclusion: Universal intake of up to 40,000 IU vitamin D per day is unlikely to result in vitamin D toxicity.”
Then two more researchers propose that vitamin D supplements have a prophylactic effect in reducing risk and severity of Covid-19.
Charoenngam and Holick, “Immunologic Effects of Vitamin D on Human Health and Disease.” Nutrients 2020, 12(7), 2097.
– “It is therefore proposed that supplementation of vitamin D can reduce the risk and severity of COVID-19 infection.”
The most evidence, right now, supports vitamin D as the best prophylactic for Covid-19. If everyone took vitamin D supplements, or received sufficient vitamin D from sunshine on skin, then the pandemic would be reduced in severity, perhaps to a great extent.
Study: Kadnur, Harshith B., et al. “Hydroxychloroquine Pre-Exposure Prophylaxis for COVID-19 Among Healthcare Workers: Initial Experience from India.” (2020).
This was an assessment of hydroxychloroquine (HCQ) as prophylactic, for its safety and effectiveness. Use of HCQ for prophylaxis in healthcare workers reduced risk of Covid-19 infection by 87%. Results were statistically significant.
Location: New Delhi, India
Participants: 334 Healthcare Workers at risk for contracting Covid-19.
Primary outcome was incidence of adverse effects.
Secondary outcome was efficacy in preventing COVID-19.
Dosage: 800 mg loading dose on day one, followed by 400 mg once-a-week.
Results: 4.4% of participants discontinued use of HCQ due to side effects. No heart abnormalities found.
“In the group taking HCQ, 2 (0·8%) tested positive compared to 5 (5·8%) in the group not taking HCQ (p=0·013). Odds ratio with HCQ intake was 0·13 (95% CI 0·02-0·85, p=0·03) and the number needed to treat was 26.”
Conclusion: “HCQ is safe at the recommended dose for pre-exposure prophylaxis of COVID-19. HCQ chemo-prophylaxis may decrease COVID-19 incidence.”
So a once-a-week dosage of hydroxychloroquine was effective in reducing risk of Covid-19 infection in healthcare workers — persons who are at high risk of infection due to their jobs.
Note that the study above showed that HCQ worked to reduce risk of infection with Covid-19 even without zinc. But other studies have shown that zinc increases effectiveness.
Ivermectin as Prophylaxis:
Vora, Agam, et al. “White paper on Ivermectin as a potential therapy for COVID-19.” Indian Journal of Tuberculosis 67.3 (2020): 448-451.
— “After critical panel discussion, all the attending doctors came to a conclusion that Ivermectin can be a potential molecule for prophylaxis and treatment of people infected with Coronavirus, owing to its anti-viral properties coupled with effective cost, availability and good tolerability and safety.”
This video from Dr. Jennifer Hibberd describes a scabies outbreak in a nursing home. This is an anecdotal report. The nursing patients were treated with ivermectin. The 4th floor patients, where the outbreak occurred received a full single-dose of ivermectin (probably 18 mg). The other patients were given a prophylactic dose of ivermectin (probably 6 mg). The staff were not treated. Then there was a Covid-19 outbreak in the nursing home. None of the patients on the 4th floor, those treated with the full dose of ivermectin, contracted Covid-19 at all, even though most of their staff were sick with Covid-19. The other floors had fewer patients become ill with Covid-19 than staff, even though the staff had a much younger median age than the patients, and all the patients had co-morbidities.
Ivermectin as Treatment:
* Gorial, Faiq I., et al. “Effectiveness of Ivermectin as add-on Therapy in COVID-19 Management (Pilot Trial).” medRxiv (2020).
~ All the patients of IVM group were cured; none of the Ivermectin patients died. “The mean time to stay in the hospital was significantly lower in IVM group compared with the controls”, 7.62 days for IVM and 13.22 days for control. Results were highly statistically significant.
* Scheim, David. “Ivermectin for COVID-19 Treatment: Clinical Response at Quasi-Threshold Doses Via Hypothesized Alleviation of CD147-Mediated Vascular Occlusion.” Available at SSRN 3636557 (2020).
“Overall mortality was 15% in the IVM group, 40% less (p=0.03) than the 25.2% mortality in the control group. For 75 patients with severe pulmonary disease (receiving oxygen at FiO2 = 50% or ventilation), those treated with IVM (n=46) had a mortality of 38.8%, 52% less (p=0.001) than the 80.7% mortality in corresponding controls (n=29). Stabilization and then improvement often proceeded in 1-2 days, even for patients who had been deteriorating rapidly from room air to supplemental oxygen at up to a 50% mixture (FiO2 = 0.5). The 1-2-day reversals of declining oxygen status in these Florida patients is consistent with rapid absorption and distribution into tissue of orally administered IVM.”
Rajter, Juliana Cepelowicz, et al. “ICON (Ivermectin in COvid Nineteen) study: Use of Ivermectin is Associated with Lower Mortality in Hospitalized Patients with COVID19.” medRxiv (2020). medRxiv.org
Conclusion: “Ivermectin was associated with lower mortality during treatment of COVID-19, especially in patients who required higher inspired oxygen or ventilatory support.”
Chowdhury, Abu Taiub Mohammed Mohiuddin, et al. “A comparative observational study on Ivermectin-Doxycycline and Hydroxychloroquine-Azithromycin therapy on COVID19 patients.” ResearchGate.net
Conclusion: “Concerning the treatment outcome, adverse effect, and safety, IvermectinDoxycycline combination is superior to Hydroxychloroquine-Azithromycin therapy in the case of mild to moderate degree of COVID19 patients. ”
Author: Ronald L. Conte Jr.